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Sticky valve on a Thunderbolt IO390

RV6-KPTW

Well Known Member
Hi all,

I have been dealing with a EGT sag on #2 with a little engine vibration just after startup for a couple of months. Never had an issue beyond a minute or so while first starting the engine until it finally occurred on departure. Under 200 hours on the engine so it was difficult to be aggressive initally.

Lycoming recommended approach is SB388 followed by SI1425A. I opted to skip the wobble test and proceed with reaming the valve guide and cleaning the valve stem.

See the photo of the shop towel. Some crud was evident after reaming and pulling the material off the reamer. It is black and does not look like lead. I looked thru and did not find anything solid or metallic valve guide material.

See the black on the valve photo. Is this common finding for sticky valves?

I am a little surprised at how little material caused the sticky valve. I have not yet tested so this conclusion might be premature. So is it me or just stuff happens?

Is this cylinder too hot? Cylinder #2 CHT is the hottest by 30 or 40 degrees. All cylinders are at 320 or so and #2 might be at 350 or 360. I had reduced the size of the original air dam thinking it was causing higher CHT issues. Cylinder 1 and 2 are hottest. Counterintuitively, would adding the original air dam back help reduce temperatures?

Are we having fun?
 

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With the parallel valve Lycomings, stuck valves and worn valve guides are some of the most common issues you'll encounter. The O-360 in my RV-8A started having valve issues around 800 hrs TSMOH (wasn't a new engine but the valves and guides were new at overhaul). I have not seen many reports of stuck valves on the angle valve engines...not sure if that's because they are less likely to have the problem, of if it's just because there are a lot fewer of them at least in Experimentals. This is the first I've heard of it on an IO-390, bum deal to have it happen after only a couple hundred hours.

There are all kinds of expert opinions out there about what causes stuck valves and how to prevent it. Some say you're running it too hot, others say you're running it too cool. Too lean or too rich. Some are convinced that certain oils are better or worse. Unleaded fuel might help but I'm not sure there's enough objective data out there to conclusively demonstrate a reduction in valve issues. I did my best to manage the engine temps and mixture carefully and ended up with valve problems anyway, and still don't know why or what I could have done differently.

With 390's priced like a new SUV, you'd think Lycoming could offer an engine that doesn't leak oil and valves that don't stick. But, no competition = no motivation to address these issues...
 
My 1 and 2 run 10-20 degree hotter as well in the -14. The fiberglass inserts in the upper cowl do a really good job of pulling air aft. I bought replacement air dams for trimming experiments with the goal of getting them all perfectly even but am not sure its worth the effort.
 
In most engine applications, valves get supplemental cooling with oil flow. Lycoming has VERY low oil flow through the pushrod relative to most all other engines. The oil comes from the hydraulic portion of the lifter. In most every other engine, the liter has a small bypass passage to send pressurized oil past the lifter and up the pushrod. For some reason, Lyc chose not to use this and rely upon bleeding oil past the clearance. The only oil that goes to the pushrod is that which leaks past that close tolerance fit of the two parts in the plunger assembly and they are hand lapped for a proper fit. Therefore, a fraction loose and you get more flow. A fraction tight and you get less flow.

If I were to do anything in your case, I would replace the plunger assembly in #2 thinking your may be a few .0001's tight. Heat causes the oil to coke in the valve guide, but if you have proper oil flow, that reduces the heat in the valve stem and reduce coking. Can't realistically expect to get a lot better on CHTs and lots of folks run 350 without sticking valves. My money is on a tight plunger assembly as the cause here.

Larry
 
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Here's an interesting article by Mike Busch on why valve sticking.
https://resources.savvyaviation.com...ticles_aopa/AOPA_2020-07_why-valves-stick.pdf

Mikes logic here is that lead is found with carbon in the build up, therefore it must be coming from the fuel. Unfounded supposition IMHO. Your oil has disspersnts that hold debris in suspension. Much of that debris is lead particles, along with carbon. Therefore the oili is filled with lead particles and is then pumped into the rocker box and coats the valve stems and guides. When oil gets too hot, it oxidizes and becomes a hard substance called Coke, with the lead particles that were held in suspension now encapsulated in the Coke. This is an equally reasonable theory for the presence of lead in the guide build up, but Mike chooses to ignore it and go with a different theory. That's his perogotive, but doesn't mean everyone should accept it at face value. If mike were correct that it is lead that is the problem, how does he explain the presence of carbon in the build up?

Unfortunately no one really knows why it is such a problem with Lyc compared to all other engines. At least my theory has a variable that is unique to Lyc engines. Not sure we will ever know the true reason. Clearly lyc thinks it is too much heat, which is why they now use exotic filled valves to keep the valve stem heat down.

Larry
 
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to get some good info I would of wobble tested all of them or reamed all of them. keep us posted when you get back running again. do you have someone to do the wobble test?
 
Why NO. 2

One observation I’ve made over the years is that it’s nearly always no.2 cylinder that has exhaust valve sticking problems. Mine did it around 350 hours.
For my Rv-10 I’ve made a duct to direct air onto the front of no.2 as per Dan Hortons baffle ramp ideas. I don’t know if it will make a difference but hoping that it gives a more uniform cooling.

Regards

Peter
 
Sticky #2 Valve

Join the club. I just had a similar problem with my Thunderbolt starting at about 185 hours. Start up was fine and about a minute or so after start, #2 would start dropping out and go cold and with a "bit of coaxing" would come back on line after about a minute. I was "15 hours" from home when this problem developed, but once running and warm, I never had a problem in flight. I made it back to base with nothing more than my morning "scare".

After doing all the normal trouble shooting of injector review, cleaning, and swapping. I even resorted to to swapping spark plugs and wires to ensure there were no spark issues. Wishful thinking makes one do a lot before deciding to ream the valves. Thus, after this journey, reaming was the next step.

While investigating the job, I was advised by Lycoming to ream them all, not just the #2 that was sticking. As suspected, #2 was quite coked up and after reaming, traveled freely. #1 and #4 had no evidence of any coking and #3 did show some evidence of build up, but was still moving freely before removal and reaming.

As far as temps go, my CHT's at 65% power (23 X 23, 50* rich of peak) for #1 & #2 are generally about 335*F and #3 & #4 are a tad cooler at around 320*F.

BTW, for those who do have to go this route, McFarland has the reamers needed for about $165 vs. Lycoming's $1300. Or you can navigate the administrative hassle between Lycoming and ACS to rent the reamer for $100 plus the cost of shipping to and from. After finding this out, I elected to buy the reamer from McFarland.
 
I am another case - mine was at 270 hours, also on cylinder #2. Like the original poster, cyl #2 is my hottest by about 20-30° (depending on conditions). However, I was typically running close to 300° (above on #1 & 2, below on #3 & 4). I also chose to skip the wobble on such a young engine - the valve was stuck enough that I had to tap the valve out with a wooden dowel. I also purchased a McMaster reamer, and the reamed material was similarly black. I reamed only the problem valve.

I followed the Mike Busch logic and I’ve attempted to increase cylinder temps since - I installed the tunnel flap (have Vetterman exhausts so it was easy) and run close to peak EGT or slightly lean in cruise, increasing my cylinder temps by 30-40° over max lean (still only 300 -350° In cruise). I have another 80 hours since the stuck valve - fingers crossed.
 
Still have not tested yet…

I found play in my pMag and am awaiting a discussion on what “excessive” means from EMagair before testing.

I can confirm that the VGR-LC4 reamer is correct - it is .5” with a .4995 pilot section. I chose this reamer specifically for the pilot concept.

Seems to me we have a group of RV14s whose CHT seem to be in the acceptable range with this problem. I would have more info on other cylinders if I had reamed all and vow to next time. That seems like a good idea.

Maybe there is nothing that can be done to avoid this issue. Depending on who you listen to, this happens because CHT is too hot or too cold.

We could
  • Cool with duct or blast tube
  • Cool by changing lifter
  • Change oil type
  • MMO?
  • Anything else?

Kiwipete is cooling by adding ducting
Keithb is increasing CHT

I am changing oil from Philips X/C 20/50 to Aeroshell W100 plus.
I will also take on playing roulette with the lifter at IR172’s suggestion - I can swap with another cylinder the next go round and see if the problem follows.

I have a crusty old timer mechanic who swears that adding MMO to the fuel is how he cures morning sickness. Anybody have experience with this?

I’ll report back on my results.
 
I am another case - mine was at 270 hours, also on cylinder #2. Like the original poster, cyl #2 is my hottest by about 20-30° (depending on conditions). However, I was typically running close to 300° (above on #1 & 2, below on #3 & 4). I also chose to skip the wobble on such a young engine - the valve was stuck enough that I had to tap the valve out with a wooden dowel. I also purchased a McMaster reamer, and the reamed material was similarly black. I reamed only the problem valve.

I followed the Mike Busch logic and I’ve attempted to increase cylinder temps since - I installed the tunnel flap (have Vetterman exhausts so it was easy) and run close to peak EGT or slightly lean in cruise, increasing my cylinder temps by 30-40° over max lean (still only 300 -350° In cruise). I have another 80 hours since the stuck valve - fingers crossed.

Yours and the other posters experience points to a conclusion opposite of Mike's. Your hottest running cylinder was the one with excessive build up. Given that experience, am surprised you decided that more heat was better. You had a perfect experiment scenario with a sample size of 4. Problem is that you don't know other variables, like the oil flow volume for each of the four.

Larry
 
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I am changing oil from Philips X/C 20/50 to Aeroshell W100 plus.
I will also take on playing roulette with the lifter at IR172’s suggestion - I can swap with another cylinder the next go round and see if the problem follows.

I have a crusty old timer mechanic who swears that adding MMO to the fuel is how he cures morning sickness. Anybody have experience with this?

I’ll report back on my results.

MMO was designed around WWII as a lead scavenging agent and was sold in 55 gallon drums to the military for mixing with Avgas in radial engines. Can't confirm that it works, only that it was designed specifically for that purpose - reducing lead deposits. That said, I still don't buy that lead is what is causing the build up in the guides, but all of the data is anecdotal and none of it seems to line up.

Larry
 
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I have a crusty old timer mechanic who swears that adding MMO to the fuel is how he cures morning sickness. Anybody have experience with this?

I’ll report back on my results.

I was going to post about MMO (old timer here?) when I read this comment. I owned a Commanche 250/260 (converted) back in the day, and our respected and very experienced A&P recommended MMO in the oil AND fuel, to help prevent notorious valve sticking in the old Lycoming O-540. So, that’s what we did. Never had a sticky valve, and had a very reliable engine. The minty aroma was a nice benefit. 😬 He referred to it as a “top end lubricant”. YMMV
 
Has anyone talked to Lycoming/Jeff about this? This is way too few hours to develop.
As a reference point, my first 14 had a Thunderbolt engine and has around 250 hours now with no issue and my buddy's engine now has around 400 with no issues. Both of us CHT are about the reported CHT here.
 
More even cooling

My reason for making a duct on the front of no.2 is to try to even out the cooling. As the bottom of the cylinder on the front doesn’t get any air and yet has quite large cooling fins. So my duct allows so air to hopefully give a more uniform temperature.
Not yet flying


Regards

Peter
 
I, too, am watching this with interest. My Thunderbolt IO-390 has 250+ hours with no problems, yet - I don’t want to jinx myself. I wish I knew what to do or not do to avoid this problem. FWIIW - I am using Phillips 20W-50 with Camguard and fly weekly. :). BTW - I have reduced the height of the air dam in front of #1 and removed the dam from in front of #2 in an effort to even out the temperatures with #3 and #4.
 
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I am seeing a strange phenomenon on my stock IO 390 EXP (100 hrs) that could possibly be related. I also see a very brief stumble/roughness at start that only lasts a few seconds but what is really strange is what happens between the time I pull power for landing at the start of my flair and when I then add a bit of power to taxi. On 100% of my flights I see my EGT on #3 drops by 100 to 150 degrees compared to the other 3 cylinders for that 20 to 30 second time frame when I transition from touchdown to taxi and then it recovers back to normal. Very occasionally I will also see it when I am at a very low idle....700 RPM or less. I have 1 impulse and 1 pmag. There is no corresponding drop in CHT. Pre flight mag checks are always fine.

Possibilities
1. One of the plugs in #3 fouling and clears when I lean to taxi. Doesn't seem to matter if I am full rich or leaned a bit on approach.
2. One of my mags has an issue at low RPM
3. a valve is hanging up.
Thoughts?
 

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I fix sticky/stuck valves all the time. Four in the last two weeks.

A few general observations.

1. Reamer is not a good tool for the job as the guides wear oblong in opposing directions at each end. A reamer will not get all of the deposits out if there is considerable guide wear. Ball hone works better, cheaper, easier to use.

2. Reported high CHT's and visibly dirty oil prevail. High CHTs cause oil in the guides to oxidize, which gets worse if oil has a lot of carbon particles in suspension.

3. Universally I find carbon deposits on springs and seats on engines with sticking valves, which tells me this problem has nothing to do with lead scavenging.

4. With sticking intake valves I almost always find wear spots on the valve tips indicating valves are not properly rotating.
 
Does anyone know a good video for doing this valve reaming job? I searched for the "rope trick" and didn't find one for the lycoming engine.
I am wondering when the valve is pushed into cylinder, how do you get it back into the valve guide?
 
A couple of responses

Bsquared - the attached screen shot from my last flight looks like yours. I do not recollect seeing this EGT sag after warmup until this flight. EGT2 typically falls off for 30 seconds or so after start, no discernible impact to CHT. This flight, it occurred for the first time on climb-out. I think I have learned that once I start to see that initial EGT sag, it will not get better all by itself.

Merdad - the rope trick is threading a rope thru a sparkplug hole, filling the cylinder with rope, and rotating the prop to press the valve into the seat. I have done this once so far. Seems pretty easy. Getting the valve back in the guide valve the first time, on the other hand, is not easy. The first time took me about 2 hours and I think the 2nd time will take 1 minute.

Merdad - I have not talked to Jeff but did talk to lycoming support. This valve issue is somewhat common. I also attended the 1 week Lycoming engine school this spring, brought this issue with me for discussion, and heard war story after war story on this topic.

IR172 suggested that increasing CHT is not supported by the data. I tend to agree so will try to cool that cylinder a little more.

Kiwipete - I am interested in your ducting idea. Can you share pictures? One other thought I had was modifying the cowl ramp to divert more air to cylinder 2. I have already reduced the air dam to the minimum. Cylinder # 4 is cooler than # 2, and maybe I can change the ratio of air distribution a little. I have already addressed any baffle leaks on #2 / 4.

RocketBob mentioned using a ball hone hone rather than a reamer. I will consider this next time. This is a brand new engine and should not have significant guide wear. Also Oil life - I am changing from 40 hours to 25 hours on the change and will see how that works out.

Interesting how often this is occurring.
 

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Merdad - the rope trick is threading a rope thru a sparkplug hole, filling the cylinder with rope, and rotating the prop to press the valve into the seat. I have done this once so far. Seems pretty easy. Getting the valve back in the guide valve the first time, on the other hand, is not easy. The first time took me about 2 hours and I think the 2nd time will take 1 minute.

I would add the breakthrough for me was an extendible magnet (a collapsible pencil sized extender) with a diameter less than 1/2 inch. Insert through the valve guide, raise the valve stem to the magnet, lift the valve to approximately aligned and coax it into the guide by withdrawing the magnet.
 
Sorry the only photos I could find show the duct I made for the rear no.5 cylinder (actually I think this photo is from another builder who’s idea I copied) and on the other photo you can just see the slot in the front ramp (behind one of the clecos) that connects to the front duct. I’ll try to get a better photo when I’m next at the hanger. The duct I made for the front ramp had to sit inside the prop governor bracket.

Regards

Peter


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3. Universally I find carbon deposits on springs and seats on engines with sticking valves, which tells me this problem has nothing to do with lead scavenging..

Bob, how does the carbon form, and what is the solution to keep it out of the springs?
 
Bob, how does the carbon form, and what is the solution to keep it out of the springs?

Carbon is a combustion byproduct. Carbon particles circulate in the oil and stick to hot parts in the engine. Changing oil on condition rather than time, running LOP on injected motors, proper temperature management, and avoiding prolonged high power settings are some ways to keep the deposits down.
 
Getting the valve back in….

I would add the breakthrough for me was an extendible magnet (a collapsible pencil sized extender) with a diameter less than 1/2 inch. Insert through the valve guide, raise the valve stem to the magnet, lift the valve to approximately aligned and coax it into the guide by withdrawing the magnet.

Indeed. This is the method I used. Two additional elements: the magnet was used to pull the valve stem thru the top sparkplug hole to clean the shaft, and I could not pull the valve thru the quide but was able to position it in the quide mouth. Significant time was spent trying to wiggle the valve to slide into the guide using long needle nose pliers without destroying anything. Eventually, the approach angle was achieved and it slid into place. .
 
Indeed. This is the method I used. Two additional elements: the magnet was used to pull the valve stem thru the top sparkplug hole to clean the shaft, and I could not pull the valve thru the quide but was able to position it in the quide mouth. Significant time was spent trying to wiggle the valve to slide into the guide using long needle nose pliers without destroying anything. Eventually, the approach angle was achieved and it slid into place. .

The Snap-On 2 prong tool is best for picking and holding the valve allowing the magnet to pull it through the guide. I fits the large diameter of the stem and will hold it securely (not dinging the cylinder wall). Only $25
 
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Agreed - I don’t see floss remaining in the valve guide. Could be one could tie it on then drop it in to the cylinder to ream.

I tried the tool mentioned by BillL for a while but finally gave up. The angle that tool engages the valve stem is acute and it just kept slipping off. I finally took my longest, skinniest, beefiest, needle nose, wrapped the jaws with gorilla tape and reached in thru the exhaust port. What ever works for you.
 
Two fingers better than four

The two finger mechanical jaws worked well for me. The fingers are large / strong enough to get a good grip on the .5" valve stem. Available from EBay.
 

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Dental floss

Maybe a crazy idea but how about using the dental floss and push it thru the guide to the cylinder. Then when all done, put the spark plugs back on and use a vacuum cleaner to draw the floss back thru the guide.
 
My sincere apology . . .

Agreed - I don’t see floss remaining in the valve guide. Could be one could tie it on then drop it in to the cylinder to ream.

I tried the tool mentioned by BillL for a while but finally gave up. The angle that tool engages the valve stem is acute and it just kept slipping off. I finally took my longest, skinniest, beefiest, needle nose, wrapped the jaws with gorilla tape and reached in thru the exhaust port. What ever works for you.

The two finger mechanical jaws worked well for me. The fingers are large / strong enough to get a good grip on the .5" valve stem. Available from EBay.

You are right, it is the two prong tool that are strong enough to pick up the valve, not 4. My memory was faulty, but the tool I have is indeed the 2 prong. I have corrected my post. Thanks for getting me back on track.
 
2nd incidence of sticking valve

I have just experienced my second incidence of sticking exhaust valve (not confirmed with disassembly yet, but symptoms are identical). Both incidents were on cylinder 2 but I have symptoms in data on cylinder 4 as well - first occurrence at 270 hours, this one at 395 hours. I will be performing the wobble test SB388C (tool on order) and SI1425C (reaming) on all 4 cylinders. Lycoming is stumped but working on it. I am forwarding them this thread as evidence of at least 4 instances in RV-14s out of only 200 flying aircraft (many very young). I will update with further info as I get it.
 
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....... wobble test SB388C (tool on order) .....

SB388C has a nice how-to section on fabrication of an "alternate tool". I did a wobble test two years ago on my own IO-360-A using a dial indicator held with an Adel clamp and enough washers under the bolt holding it to get the proper clearance. Here's the text from SB388C:

A tool may be fabricated to measure wobble. Tool must measure parallel to the rocker at the following height above the rocker box cover surface of the cylinder (machined O.D. surface of rocker box cover surface).
Angle Valve Clearance – 0.750 ± .015
Parallel Valve Clearance – 1.190 ± .015


The adapter over the valve stem is piece of 5/8" dia round stock with a 1/2" hole drilled in the end and a slot to allow tightening on the stem.

20210328_161918.jpg 20210328_161950.jpg
 
KeithB,

Interesting that it is happening again on Cyl#2. My issue as well.

Did you find carbon on the previous issue?

What are your CHTs on that Cyl? Oil Type and change interval?

Thanks
 
KeithB,

Interesting that it is happening again on Cyl#2. My issue as well.

Did you find carbon on the previous issue?

What are your CHTs on that Cyl? Oil Type and change interval?

Thanks

On the first incident, the valve was so snug I had to tap it out with a wooden dowel. The reamer removed a black gum/goo - very tar like.

Regarding CHTs, cylinder #2 is my hottest, though on an RV14 that is relative. My engine has Vetterman dual trombone 2-to-1 pipes that come out outside the tunnel - this improves already robust cooling. During the engine’s first 250 hours, my cruise CHTs were 2 cylinders in 290s, 2 in 30x’s. Just before my first valve incident, I installed the OP-62 tunnel cooling flap kit. This raised my CHTs by about 30°. I also changed my operating profile, cruising typically “on the lean side of peak” rather than LOP - basically higher power settings with higher EGTs. Cruise CHT on #2 has been about 350°. My cylinders have never seen 400° - ever.

I use Phillips XC 20W50, change target is 40 hours, but never over 50. Regular (but not always) oil analysis. Last report (Blacksone) said:
“ KEITH: N314KC's latest report doesn't raise any concerns. Wear metals are holding steady following the valve work last year, which is nice to see. There are no signs of any developing issues in the wear trend. The physical properties of the oil are all in good shape, too. The high flashpoint rules out any measurable fuel dilution. No water contamination was detected either. Keep up the good work with this IO-390!”
Silicon level was 4, down from 5 on the previous analysis - both very good values.

Boroscope and reaming starts today.
 
The reamer removed a black gum/goo - very tar like

Not wanting to impede on a IO-390 thread, but I can share the following: I had my share of sticking valves as well: a couple on smaller Continentals, then on a O-320, and now on my O-360.
Using different gas, oils and power settings on all of those...

And all the deposits I found in these cases were very similar to what you posted, though I wouldn't call it tar like, but more carbonised oil like.

Alas, I had sincerely hoped that Lyco improved on that problem...
 
These kind of issues really concern me. Am I gonna throw down $60,000.00 for an engine that gets sticky valves that need attention in approximately 250hrs? I have considered alternative engines and this really pushes me in that direction despite my desire to stay plug and play with the IO-390-exp. I get sick thinking of spending that much on a garbage engine. Please tell me I'm off base here and overreacting!
 
I like your optimism Vlad! If you are the same guy on YouTube building an RV-10, I also have enjoyed your videos so thank you! If that's not you well I still appreciate the tip (MMO) and good attitude.
 
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Use a lot of MMO, fly often and you will make at least two TBOs :)

Vlad,

Do you add MMO directly to the engine oil, and if so, how much do you add per oil change (or other interval)? Do you add MMO to any other areas?

thanks,
-Alex
 
Vlad,

Do you add MMO directly to the engine oil, and if so, how much do you add per oil change (or other interval)? Do you add MMO to any other areas?

thanks,
-Alex

Hi Alex,

I add 8-10 ounces during oil change and the same amount every 5 to 10 hours depending on the trips. Also I add it to the fuel 1:300 ratio or so. On average my engine consumes a gallon of MMO every two months.
 
Hi Alex,

I add 8-10 ounces during oil change and the same amount every 5 to 10 hours depending on the trips. Also I add it to the fuel 1:300 ratio or so. On average my engine consumes a gallon of MMO every two months.

Thanks, Vlad - seems like you get very good results with it!

_Alex
 
Vlad - ratio MMO ?

I add 8-10 ounces during oil change and the same amount every 5 to 10 hours depending on the trips. Also I add it to the fuel 1:300 ratio or so. On average my engine consumes a gallon of MMO every two months.

I assume that ratio 1:300 is Gal MMO:Gal fuel? Da, Nyet?
 
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