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Vapor Lock RV-12 Rotax 912ULS

Piper J3

Well Known Member
I may be joining the “Sinker Club” for 2nd time. Today I did several TO/Landing to full stop at a remote airport and on last TO had horrible stumble/vibration at about 500 AGL before turning crosswind. My first thought was I lost a tip of one propellor blade. I’m guessing power loss of about 10-20% - enough power loss to eliminate climb. I pulled throttle back to see if vibration would get better and it got a little better but not total solution. I checked both ignitions and they were working equally well. So, I keep power reduced and turned 180 degrees and landed on runway in opposite direction. Yeah, I know – don’t do that. Engine ran and tested well on the ground, so I did a flight and stayed in traffic pattern, and once satisfied everything OK, I flew 30nm back to home airport. While all this was happening, I never experience fuel smell. I will weigh floats tomorrow and thinking about bumming Marvel Schebler floats from friend who is waiting to do installation in his own RV-12.

Running fresh 93E10 with 75F OAT, so possibility of Vapor Lock? Also, fuel purchased today may still be Winter Vapor Pressure...

A couple questions:

• Is this normal "sinking float" failure mode that must folks are seeing?

• Is everybody happy with the newest Marvel Schebler Floats MS80-430?

Thanks for listening…
 
Jim

Your symptoms are exact to mine last May if you remember . It was indeed winter blend that cause exactly the same situation.

I though floats right away . It was not. It was winter blend vapor locking . You can go back and look at the old posts on this . about a year ago. When the weather started getting warm.

Brad Stiefvater
Salem SD
124BJ
 
^^^ Right ^^^

Now I’m wondering if removing the cylinder cooling shroud maybe increases under-cowling temperatures during ground operations. I just finished repairing a cracked engine mount, installed new high performance silicone coolant hoses, and changed out rubber engine mount isolators. While I was doing this work, I removed the fiberglass cylinder cooling shroud as per latest Van’s KAI. Maybe when doing a lot of TO/Landing/Ground ops the under-cowling temperatures get high enough to boil fuel in the carb float bowl?

Today was third shakedown flight with previous two flights still using last year’s fuel which I’m sure was summer vapor pressure. Today’s flight used newly purchased 93E10 Mogas which I’m quite sure is still being sold as winter blend.

I think lesson to be learned is reduce ground ops to a minimum when using winter vapor pressure fuel and OAT is +70ish...
 
I removed my shroud 10/2/20, when I changed to silicone coolant hoses. That was 146 hours ago. I did not notice any temperature differences after the change.

The floats were changed to Marvel Schebler Floats MS80-430 on 1/9/21, 60 hours ago. The floats I had in it weighed good but I didn't want to have any future issues.

The plane is hangared in Southern California where it gets quite hot and we have EPA regulating our gasoline. Costco 91 octane is used exclusively.

One time before all the changes, my wife with an instructor experienced a power loss, it did not quit but had a power reduction on climb out. It was a 110 degree day and they had a long wait getting out. The instructor related the incident upon landing, he said he reduced power then came back up on it and it was running fine. They flew another .7 afterwards with no further problems. I pulled the Dynon logs and the oil temp was 180f on the takeoff roll and peaked at 256f. in the climb.

I personally have not had any running issues before or since but I do not let the temps climb that high.
 
I agree with above. My temps – (2) EGT, (2) CHT, and oil temp all same with/WO cylinder cooling shroud. Oil temps in green arc. My concern is with ground ops. It would be nice to have sensor to measure under-cowling temperature as indicator for prelude to vapor lock.

I’m really thinking my engine stumble/vibration problem was excess heat buildup from ground operations while using winter vapor pressure fuel. Today I will fly again with fresh winter fuel. I will fly early morning while OAT is cooler and I will keep ground ops to a minimum. I have ordered Marvel Schebler epoxy floats and will install soonest.

If my research is correct, winter fuel changeover doesn’t occur until May 1 at fuel terminals and gas stations have until June 1 to complete the changeover to summer gasoline.
 
What you’ve described regarding running winter blend fuel and heat soaking on the ground is quite possibly the cause of your problem. Did you shut down and restart at all during these ground ops? Depending on the specific winter blend, OAT and heat soaking you could be boiling your fuel. The bigger the difference between winter temps and warmer present temps the greater the potential for problems.

Personally, I would not run in hot temps with winter blend fuel, ever. Especially winter fuel from northers states where it gets friggin cold and blends are made for the more extreme cold temps. Much better to put 100LL in the engine of summer fuel isn’t available, to better ensure you don’t have potential vaporization. The vapor pressures on winter blend fuels can be remarkably different than standard blend fuel in some locales. Fuel blended for cold-air ops just won’t perform in hot environments. Engines can potentially quit. That’s definitely one of the potential risks one must actively understand and manage when running auto fuel. 100LL with a little Decalin scavenging agent added can bring a lot of Pearce of mind when an appropriate auto fuel isn’t available.
 
Thanks for your input Greg. I wonder if adding a series of louvers on the top cowling would keep temps in check?

As an experiment, I’m buying a two-channel digital temp sensor with type-K thermocouples for $19 on Amazon. Thermocouple leads will be long enough to measure temp of each carb float bowl to determine if fuel is near boiling point.

It would be really nice if my D-180 could input two additional temp sensors.
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Thanks for your input Greg. I wonder if adding a series of louvers on the top cowling would keep temps in check?

As an experiment, I’m buying a two-channel digital temp sensor with type-K thermocouples for $19 on Amazon. Thermocouple leads will be long enough to measure temp of each carb float bowl to determine if fuel is near boiling point.

It would be really nice if my D-180 could input two additional temp sensors.
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Louvers would allow a little more hot air to escape (like with the 12iS cowling). But it would not meaningfully impact the fact that winter blend fuel will boil/vaporize at a lower temperature (often MUCH lower) than summer blend or 100LL fuel will. I would not look to making physical changes to solve a problem that has a root cause in the actual fuel being used in an incorrect environment. Upper-midwest winter blend fuels made for very cold temps, for example, can have a VERY different vapor pressure than standard/summer-blend fuels. Fuels really need to be used in the ambient temperature environments they're blended for.

Opening the oil door (when shut down of course) can make a significant difference in reducing how hot the cowl gets as it heat soaks, and for how long. But it still gets hotter. Just physics. :)
 
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One of the flight schools in Boise, ID that posts here had the same problem in March or April of 2020, vapor lock and loss of power on take off.

Adding 10 to 20% of 100LL to the rest of the Mogas solved the problem.

Cammie Patch was the author of that comment, if you want to look it up, as they don't post that often.
 
THERMOCOUPLE

Piper J3, the Dynon D-180 has a thermocouple input on EFIS pins 27 & 28. If that input is free,
a type J thermocouple can be connected. Omega has part number WTJ-14-36 for $14.
 
Piper J3, the Dynon D-180 has a thermocouple input on EFIS pins 27 & 28. If that input is free,
a type J thermocouple can be connected. Omega has part number WTJ-14-36 for $14.

Joe -

Where would the temps display? I think the screen position where MAP is can be assigned to a different sensor.
 
Here is an old picture showing gascolator temperature.
I moved the thermocouple so that now it measures voltage regulator temperature.
The ammeter might have been in that location. The ammeter never worked anyway.
 

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What you’ve described regarding running winter blend fuel and heat soaking on the ground is quite possibly the cause of your problem. Did you shut down and restart at all during these ground ops? Depending on the specific winter blend, OAT and heat soaking you could be boiling your fuel. The bigger the difference between winter temps and warmer present temps the greater the potential for problems.

Personally, I would not run in hot temps with winter blend fuel, ever. Especially winter fuel from northers states where it gets friggin cold and blends are made for the more extreme cold temps. Much better to put 100LL in the engine of summer fuel isn’t available, to better ensure you don’t have potential vaporization. The vapor pressures on winter blend fuels can be remarkably different than standard blend fuel in some locales. Fuel blended for cold-air ops just won’t perform in hot environments. Engines can potentially quit. That’s definitely one of the potential risks one must actively understand and manage when running auto fuel. 100LL with a little Decalin scavenging agent added can bring a lot of Pearce of mind when an appropriate auto fuel isn’t available.

What Greg said is correct. Avoid winter pump gas, try to buy from high quality Shell or similar gas stations (avoid brand x - I purchased an outboard motor recently and the owner of the shop hated Costco, most supermarket and 7-11 type gas stations - he said stick with Shell, Mobil or Chevron - higher quality gas sold) - also avoid 93 or other octanes that don't have high turnover. Top off with a little 100LL and an oz of decalin. YMMV.

I also upgraded to the newer high pressure Facet fuel pump, haven't had a vapor lock symptom since.
 
I hear what everyone is saying about not using Winter blend auto fuel (lower vapor pressure) in warm weather. I experienced vapor lock on the ground several years ago and now it happened again in the air – see post #255 above.

All this gets me thinking… obviously, automobiles don’t have a problem operating with low vapor pressure fuel in warm temperatures - either carb or fuel injected. Likewise, lawnmowers, motorcycles, chainsaws, etc. – none of these have problem with low vapor pressure fuel when operated in warm OAT. I suspect even Rotax 912 in either loosely-cowled aircraft, or no cowling like Air Camper, don’t have this problem.

The RV-12 has a tightly-cowled engine with two very small (2.5”) round air inlets. In addition, hot air from both the oil cooler and the water radiator dump into the cowling for exit at bottom of firewall opening. During ground ops, hot air can stagnate in the cowling causing elevated temperature of fuel lines and carburetors. The recirculating fuel line back to the tank does nothing to cool fuel in the individual carb feed lines or the carbs themselves. Also, when engine is idling on ground, fuel flow is minimal so fuel has huge opportunity to elevate in temperature.

Where am I going with this… It’s my contention that the RV-12 needs better cooling during ground operations. Maybe something similar to the cowl flap on a Cessna 182. Perhaps a louver on the top of the cowling to spill excess heat while airplane is on the ground. Could be a permanent louver like on the 12iS or perhaps a spring-operated flap (C-182) that would open on the ground and automatically close at higher airspeeds. I think for ground ops, the prop blast over the louvers would act like a venturi and hot air will get sucked out of the top of the cowling…
 
I hear what everyone is saying about not using Winter blend auto fuel (lower vapor pressure) in warm weather. I experienced vapor lock on the ground several years ago and now it happened again in the air – see post #255 above.

All this gets me thinking… obviously, automobiles don’t have a problem operating with low vapor pressure fuel in warm temperatures - either carb or fuel injected. Likewise, lawnmowers, motorcycles, chainsaws, etc. – none of these have problem with low vapor pressure fuel when operated in warm OAT. I suspect even Rotax 912 in either loosely-cowled aircraft, or no cowling like Air Camper, don’t have this problem.

The RV-12 has a tightly-cowled engine with two very small (2.5”) round air inlets. In addition, hot air from both the oil cooler and the water radiator dump into the cowling for exit at bottom of firewall opening. During ground ops, hot air can stagnate in the cowling causing elevated temperature of fuel lines and carburetors. The recirculating fuel line back to the tank does nothing to cool fuel in the individual carb feed lines or the carbs themselves. Also, when engine is idling on ground, fuel flow is minimal so fuel has huge opportunity to elevate in temperature.

Where am I going with this… It’s my contention that the RV-12 needs better cooling during ground operations. Maybe something similar to the cowl flap on a Cessna 182. Perhaps a louver on the top of the cowling to spill excess heat while airplane is on the ground. Could be a permanent louver like on the 12iS or perhaps a spring-operated flap (C-182) that would open on the ground and automatically close at higher airspeeds. I think for ground ops, the prop blast over the louvers would act like a venturi and hot air will get sucked out of the top of the cowling…

https://vansairforce.net/community/showpost.php?p=1438427&postcount=39
 
And another thought... The carbs on RV-12 do not intake cold air like most other airplanes. So, the hot under-cowl air contributes to increase carb body temperatures. Lots of things going in the wrong direction temperature-wise...
 
And another thought... The carbs on RV-12 do not intake cold air like most other airplanes. So, the hot under-cowl air contributes to increase carb body temperatures. Lots of things going in the wrong direction temperature-wise...

That was a trade off so that carb heat was not a necessity on a LSA aircraft, and icing of the carburetors is now a non issue.
 
A sensitivity to the use of winter blend fuel in warmer temps is not limited to just the RV-12.
There are many other aircraft models that have had issues as well.

Avoiding use of 100% winter blend auto fuel in hot temps is the best course of action. This is standard practice for most people using it in Lycoming power aircraft as well.
 
And another thought... The carbs on RV-12 do not intake cold air like most other airplanes. So, the hot under-cowl air contributes to increase carb body temperatures. Lots of things going in the wrong direction temperature-wise...

We have done quite a bit of testing while instrumented with temp probes under the cowl and in flight the induction air temps are not elevated a significant amount to where it would increase the temp. of the carburetors.
 
We have done quite a bit of testing while instrumented with temp probes under the cowl and in flight the induction air temps are not elevated a significant amount to where it would increase the temp. of the carburetors.

I would guess there is plenty of cool air ingested during flight. It's the ground ops that cause elevated carb body temp and elevated temp of the fuel in both hoses feeding the carbs and the fuel in the float bowls themselves.
 
I would guess there is plenty of cool air ingested during flight. It's the ground ops that cause elevated carb body temp and elevated temp of the fuel in both hoses feeding the carbs and the fuel in the float bowls themselves.

I don't disagree.
And like I said that is a problem to some degree with just about every 912 powered airplane that has a full / at least somewhat aerodynamic cowl.

If proper fuel and ground procedures (the aircraft documentation recommends the oil door be left open in hot temperatures when parked on the ground to vent the engine compartment) are used, it is generally not a problem.
 
A quick question then… Are the louvers in the 12iS top cowl for add’l cooling? Or are they there to make it look like a Buick Electra 225 (Deuce & ¼)?
 
A quick question then… Are the louvers in the 12iS top cowl for add’l cooling? Or are they there to make it look like a Buick Electra 225 (Deuce & ¼)?

Both

Style sells ;)

Seriously, they are for cooling but not in the same context as you are questioning.

Rotax has some very specific specification requirements for the design of a 912iS engine installation. Many of them are requirements for max. temp of electrical components.
That is the purpose of the louvers on a 12iS. Ground cooling of the ignition coils (they are located directly under the louvers).

BTW, we are very proud of the design of the engine installation on the 12iS.
It 100% meets all of Rotax's requirements (I am not sure that all manufacturers can truthfully say that).
We put a LOT of effort into that and the higher ups in Rotax were quite impressed with the design when it was introduced at OSH 2017, and they requested the opportunity to do a photo shoot with the cowl removed.

There are also design requirements for the 912ULSl, and we put an equal amount of effort into meeting all of those as well.
 
Style sells ;)

Scott –

Thanks for response. Glad I could add some levity to your day.

You’re probably too young to have experienced the real heavy iron out of Detroit... ’59 was a big year (read: big fins) for Cadillac (vertical) and Chevrolet (horizontal). The North American F-86 Sabre was a huge influence on US automotive design in that era.

Good to see Van’s Aircraft prescribes to Form follows Function.

Have a great weekend…
 
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Carb Temp Sensing...

I bought a two-channel temperature sensor with 1-meter thermocouples on Amazon for $13.99 (obviously, non-certified at this price point). I intend to temporarily install using 3M double-sided tape to bottom of instrument shelf and operate with 9V alkaline battery. Thermocouples will press against carb float bowl and be pinched between bail wire that fastens float bowl in place. I’ll use some thermal paste to get good thermal conductivity. If unit looks durable, I may install in the instrument panel and upgrade thermocouple leads to Type-K with fiberglass encased wire.

Since experiencing vapor lock power loss/severe vibration last week on climb-out, I’m a little anxious about flying in Spring weather conditions when OAT is warm. This is an attempt to get real-world fuel temperatures during ground ops to see if vapor lock can be foreseen before it becomes imminent.

I get the idea of using 100LL or mixing avgas/mogas to raise vapor pressure. I fly from a private strip so I’d have to fly to local airport to fuel. While fueling, the engine will heat-soak even with oil door open combined with add'l taxing to runway which I want to avoid. My plan is to continue using 93E10, fly mornings when OAT is cooler, and avoid all ground ops. So, no intermediate stops – fly and return to base. No landings with ground taxi until refineries and fueling stations switch over to Summer vapor pressure blend.

https://www.amazon.com/gp/product/B07WS11X45/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1
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This is interesting, I’ll be following you.
I would start a new thread specifically dealing with the vapor lock.

It is my understanding the vapor lock occurs in the fuel lines not in the bowl. Maybe find the hottest fuel line location and monitor it?
 
If vapor lock occurs in the fuel lines, then perhaps add’l insulation on top of the existing Fire Sleave is warranted.

Amazon Aircraft Dept again to the rescue with both 1” ID x 36” L and 5/8” ID x 36” L Vapor Block Fuel Line Sleeve @ ~$16.

Just like Ross Perot used to say... "We'll raise the hood and try to figure out what's going on".

https://www.amazon.com/Design-Engin...+line+insulation+sleeve&qid=1618254374&sr=8-3
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Two-channel temperature sensor is temporarily installed. Thermocouples pinch nicely between float bowl and bail wire. Total install time was 15 minutes. Runway too wet for flying today. Flight test tomorrow. News @ 11…
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I have asked moderators to start a new thread RV-12/RV-12iS > Vapor Lock. I also asked that post #255 and up from this thread be transferred to the new Vapor Lock thread. So, hopefully that will be done. I think this topic should have its own thread to make it searchable in the future.

So, yesterday I temporarily installed a two-channel temperature sensor with thermocouple probes pinched against both carburetor float bowls. I flew this morning to two outlying airports with a landing to a full stop and long taxi back to departure runway at each. Flight time was 60 minutes.

Observations from this morning’s flight:

• OAT – 45F

• All temperatures reported below at right carb - right carb is consistently 5F higher than left carb on ground and in the air. I believe the proximity of the oil tank is causing additional heat on right side.

• Temp during climb – 96F

• Temp during cruise @5500 RPM – 84F

• Ground ops taxing – 98F


Now, here is the eye opener… At completion of the flight, I pushed airplane into hanger and opened oil door to see how quickly engine compartment cooled down – it didn’t. Temperatures continued to climb for 5 minutes until max temp of 116F was reached. My oil door opens to near vertical and lots of heat spills out.

So far, I don’t like what I see… 45 OAT, 98F ground ops, and oil door not spilling off enough heat. Weather in Ohio is forecast for cool temps for next two weeks so not much more to learn for a while. My concern is - what’s going to happen during summer temps?

Next steps… with left carb consistently 5F less than right carb, there is no need to measure both carb temps and only the higher right carb sensor will remain. I’m contemplating using the left thermocouple to measure temperature of one of the fuel hoses. Perhaps measure temp of a fuel hose near the “T” junction fastened to the manifold crossover tube. I suspect fuel hoses routed above the engine run pretty warm.
 

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A work in progress...

Thermocouple at left carb float bowl is redundant, so I re-purposed it to measure temperature of fuel line where mechanical fuel pump splits at T-fitting to supply each carburetor. I snuck the thermocouple under the Fire Sleave and it is pressed against the stainless-steel braid on the Teflon fuel line. This should be pretty good measurement of actual fuel temperature just before fuel is delivered to the carbs and access fuel is returned to the tank. I forgot to plug in engine heater and temp is 38F so test flight will be conducted over the weekend.

Next steps…

  • Purchase and install Design Engineering 010669 Vapor Block Fuel Line Sleeve and install on all fuel lines FWF. 5/8” ID x 36” and 1” ID x 36”
  • Make insulated cover for metal T-fitting and Banjo’s that clamp to manifold crossover tube.
  • Insulate crossover tube to eliminate heat sink into T-fitting.
  • I have ordered FAC-40135 Facet Cube 12v Fuel Pump,1/8 NPT, 4.5-6 psi per Van’s Notification 18-07-12. I have never had low fuel pressure but I think now is the time to install new pump rated at higher output pressure to help prevent vapor lock.
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Might even consider adding a louver to top cowling to extract heat… particularly during ground ops. Louver needs to be plastic so GPS antenna continues to “see” satellites.
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I am starting a new thread titled “Vapor Lock RV-12 Rotax 912ULS” so that it will searchable and specific to this issue. On 4-6-21 I experienced vapor lock that caused severe vibration and power loss on climb out.

I have asked Doug Reeves to have a forum moderator move/copy posts #255–286 from RV-12/RV-12iS > New member of the “Sinker Club” (carb floats) to this new thread.

If moderators don’t comply, I strongly suggest readers of this thread familiarize themselves with the posts listed above.

All future posts pertaining to Vapor Lock RV-12 Rotax 912ULS will be listed here…
 
Jim, what were the flight conditions? I have experienced low fuel pressure/high fuel flow alarms on climb out in Phoenix summer when I secure my electric pump, but starting the electric pump has always cleared them. I’m curious to know what environment is worse than PHX in August.
 
How do you "secure" an electric pump on an RV-12. Is not the pump on all the time? To "secure" (turn off) the electric pump on my RV-12 (SLSA) I would have to pull the fuse.
 
Vapor lock occurs in our planes when the under cowl temps rise to a level that causes the fuel to turn to vapor and block the fuel from traveling in the line to the carburetors. It primarily happens when winter blend ethanol fuel is used on a hot day but it can happen even with summer blend if the temps get high enough.

When it happens, depending on where in the fuel line it occurs, it can affect one or both carburetors. The carburetor(s) will starve for fuel and either loose power or quit. The most common time in a flight for it to happen is on takeoff after being on the ground getting hot with low cooling air flow through the cowl.

The carburetor bowls hold about 18 seconds of fuel at full power if vapor lock is recognized early that time would be valuable.
The EFIS will show a low fuel flow rate, this would happen if the bowl quit filling, hence potentially vapor lock. The flow rate with the engine off is about 1.5 GPH. I would think anything below 3 GPH would be suspect of vapor lock.

I wonder if it is possible to have an alarm warning of low flow rate.

Keeping an eye on the flow rate during climb out on hot days could warn of a potential emergency.
 
How do you "secure" an electric pump on an RV-12. Is not the pump on all the time? To "secure" (turn off) the electric pump on my RV-12 (SLSA) I would have to pull the fuse.

It has been a hotly debated modification. Many owners have installed a fuel pump switch and only run the electric fuel pump at certain times, such as on start up, take off and below 1000 ft. I too have a fuel pump switch in my airplane.

https://vansairforce.net/community/showthread.php?t=47694&highlight=fuel+pump
 
Jim, what were the flight conditions? I have experienced low fuel pressure/high fuel flow alarms on climb out in Phoenix summer when I secure my electric pump, but starting the electric pump has always cleared them. I’m curious to know what environment is worse than PHX in August.

75F OAT, fresh 93E10 from Tier 1 supplier (winter blend vapor pressure fuel), multiple TO / landings / taxi back. On third take off, at approx. 500’, I experienced severe vibration and power loss. Vibration felt like part of prop was missing. Now, thinking more about this, I estimate power loss near 50%. Not good.

Regarding electric fuel pump… Van’s Aircraft has been very vocal, and sending clear message, that fuel pump needs to run 100% of time and not be shut off on ground or in the air. To do so, is inviting vapor lock by lowering fuel pressure.

It is my contention that the RV-12 Rotax 912 install is too tightly cowled leading to excessive temperature buildup. Fuel lines are routed on top side of engine and are prone to heat soak when fuel flow is low during ground ops.

Vapor lock can most certainly happen with summer blend vapor pressure fuel if under-cowl temperatures are allowed to rise.
 
After readings these posts I'm wondering how common a problem this is. I have 375 hours on my -12 and have flown only in the south with OAT at or above 90 in the summer and have never experienced vapor lock or any problem that resembles it, my electric pump runs constantly, no switch. Many others fly out west with much higher OAT's, living in the south I'm not sure if we get winter grade fuel so that could be what my experience lacks...
 
After readings these posts I'm wondering how common a problem this is. I have 375 hours on my -12 and have flown only in the south with OAT at or above 90 in the summer and have never experienced vapor lock or any problem that resembles it

I don't think it is a common problem at all, however, it is problem to be avoided at all cost. I have ~640TT and experienced vapor lock in the air for first time last week.

I should not speculate, but it is possible that some of the RV-12 power-loss accidents may be attributed to vapor lock.
 
The problem with trying to predict when or why you might get into a vapor lock situation is there are far to many variables. Eythonal based fuels start degrading the day they are refined. They may not meet minimum specs 30 days later. When you purchase the fuel it may already be older than 30 days. In addition as mentioned the fuel is blended to different specs depending on location, time of year, manufacturer ect..
This time of year is when we see vapor lock issues. A aircraft may not have flown much or at all in the last few months with winter weather, last fuel pumped in might be winter blend. You have low vapor pressure fuel to start with that is degraded from sitting. Mixing some new fuel in does not fix the old fuel!
All of the above also applies to non eythonal fuel but it’s typically stable for at least 90 days. AvGas I believe is blended to be stable for a year. What really scares me is stored E fuels. Often it’s for aircraft use where someone has a trailer or truck equipped with a tank. The fuel might be very old before it’s pumped into the aircraft. Eythonal based fuels should never be stored prior to aircraft use. It’s questionable if non eythonal auto fuel should be stored either.
In short using any type of auto fuel to quote a famous movie is like a box of chocolates. You never know what you will get.
 
After readings these posts I'm wondering how common a problem this is. I have 375 hours on my -12 and have flown only in the south with OAT at or above 90 in the summer and have never experienced vapor lock or any problem that resembles it, my electric pump runs constantly, no switch. Many others fly out west with much higher OAT's, living in the south I'm not sure if we get winter grade fuel so that could be what my experience lacks...

Agreed, RV12's arent falling out of the sky. And Piper J3 is right, it's an issue to avoid at all costs.

The solution seems simple enough. Mix winter blend with a bit of 100LL during those 'iffy months' of Winter blend and warm outside temps. But I definitely respect the research and am curious on his findings.
 
I don't think it is a common problem at all, however, it is problem to be avoided at all cost. I have ~640TT and experienced vapor lock in the air for first time last week.

I should not speculate, but it is possible that some of the RV-12 power-loss accidents may be attributed to vapor lock.

Let's see. You've flown this -12 about 600 hours and this is the first time you experienced this. What's different this time? Did you do something to the engine compartment configuration recently, like remove the cooling shroud?
 
Yes, I had to repair cracked engine mount and did 5-year rubber at same time. Also, removed cooling shroud per latest KAI from Van's. Oil temp, CHT's, and EGT's remain as before which confirms what Greg Hughes has said in the RV-12 Forum.

Heat soak after engine shutdown may be increased with fiberglass cooling shroud removed...
 
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Jim, Have you downloaded the Dynon logs for your incident and looked for any clues like oil temp, air temp, fuel pressure, flow rate, etc?
 
Yes, I had to repair cracked engine mount and did 5-year rubber at same time. Also, removed cooling shroud per latest KAI from Van's. Oil temp, CHT's, and EGT's remain as before which confirms what Greg Hughes has said in the RV-12 Forum.

Heat soak after engine shutdown may be increased with fiberglass cooling shroud removed...

Actually, the latest KAI for the ULS installation uses a different cowl, different oil and coolant radiators and placement.

I'm playing devil's advocate here I guess, but I think removing the cooling shroud may be a significant factor in what you are experiencing.

"The troubles started when the mechanic opened his toolbox", author unknown.
 
Vapor lock incident

After reading this post I am inclined to share my experience of vapor lock. Same engine (912) but different type aircraft. Vapor lock with this engine is not specific to the RV-12.

Aircraft: 2016 Rans S-20 Raven
Engine: 2016 Rotax 912 ULS
Fuel: Mogas Nampa Idaho: KMAN
Ramp Temp 103F
Facet boost pump: On

Flown the aircraft many times in high ambient temps and never had an issue. On this day I was working on the aircraft and did a 20 minute test hop. No issues. The plane sat in the sun for a half an hour and was flown again.
Run up was fine as well as the takeoff roll.

Thirty feet in the air the engine stumbled badly, shaking etc. I pulled the power to idle and landed on the available runway.

In addition, I affixed a Lyc carb temp probe to the throat of the left carb to help detect Carb ice and high cowl temps. I tied it into my Dynon Skyview.

Routinely I have seen carb temps often in the 130 to 140F range on a 75F day. The highest temps recorded are typically 5 to 20 minutes after shut down.

Hope this helps,
Jim
 
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I'd do a couple of things.

1. Run 100LL with Decalin added, at around 10%, while this winter fuel is problematic or until #2 is completed also while winterized fuel is still a problem. You might want to run Shell AeroSport 4 Plus semi synthetic motor oil in the interim, while running the smidgen of 100LL.

2. Reinstall that fiberglass shroud around the engine.

3. Continue monitoring.

But, that's me, there's pilots with way more experience than me with Rotax engines on here.

I'd probably also wait at least an hour after landing before going up flying again, with the plane parked nose into the prevailing wind and the cowling port open to facilitate cooling inside the cowling.

I don't think they do much to winterize the fuel here in the Los Angeles Basin, but then I've only flown at 9500 ft altitude 1x doing my night time XC lesson in Feb. over the Pacific Ocean mostly, not the hot part of the day, when it could be problematic.

I drove an air cooled 1967 VW Beetle for 6 years and probably close to 90k miles, that I'd modified and bumped the compression ratio up quite a bit, as a young man, and drove it pretty hard... can't say I ever had a no start condition due to vapor lock, but that was in the late 1970's and early 1980's, maybe fuel additives weren't as problematic then as now.
 
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