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0-320 overheating on first take off

Flyer2017

Active Member
We have a 9A made in 2003. We bought it in 2017. It has always had CHTs in the low 400 range on first take off at our 4600 ft airport. We added a Surefly mag replacing the right mag last year. Now, instead of CHTs in the 400-410 range, we are getting CHTs in the 415 - 430 range.
I know part of that rise is the Surefly mag that has a hotter and longer spark and at WOT has the spark timing advanced. The CHTs seem to come down into the 370 - 390 range after we pull back the throttle and/or after the vernatherm lets the oil into the oil cooler. The vernatherm seems to open at about 180 - 185 F. We are getting the higher CHTs at 60 F ambient temps. In summer, it's worse.

I plan to replace the 20 year old baffling around the engine and can see on the inside of the upper cowling the dirt marks where air is escaping.

Is there a lower temperature vernatherm that would allow oil through the cooler at a lower temperature? Or is there an adjustable one? I only see one for Lycoming engines online.

I discussed going to a different jet on the MS MA4-SPA 10-5217 carb which maxes out at 12 - 13 gallons/hour. My A&P thinks if I go to the next larger size jet (actually a rebuilt carb) I could get 13.5 to 15 gallons/hour at WOT and use the extra gas for cooling.

I've read most of the discussions here, including the ones that advise to modify the metal baffling to force air over fins that may be starved for cooling air now.

Any advice on what to do first?
 
It sounds like the vernatherm is doing what it's supposed to do. The oil IS cooler when the engine isn't warmed up, so don't fix it if it isn't broken.

I don't know enough about the Surefly system to comment on what that might be doing, but advanced timing will raise CHTs.

Regarding the baffling & seals, you've acknowledged that there's opportunity for improvement--so I would first work that out before you start changing other components. If it's twenty years old, the seals have probably lost a lot of flexibility and you could be make significant gains with relatively little cost and effort.

As others have said on this forum many times, every little crack, gap, or leak that's not pushing air past a cooling fin is wasted air. I thought I originally had my cylinders sealed up pretty well, but my EAA Tech Counselor and other RV owners have proved otherwise. Get a flashlight and see what you can see from top to bottom. Don't assume the original owner had it perfect. If you're not sure what to look for, get someone who does. An hour or so with a tube of red RTV can make a big difference.
 
Hotter/longer spark duration will not affect CHT's. Spark timing (when it occurs, not how long) WILL affect CHT's, as will mixture.
 
Suggest you try one change at a time & test to gauge each result.

1- You mention CHT temps are slightly higher after Surefly was installed. I suggest you start here. Retard the Surefly base timing by 2 degrees & test. Repeat with another 2 degrees Retart & again test. Stop adding Retard when you notice your ‘mag drop rpm’ is equal between the mag & Surefly during your run up check.

2- Tackle the obvious baffle seal issues next. There is a recent thread that suggests ideas on improving cooling effectiveness, as well many other threads on this subject. This should have a definite effect on CHT in both climb & cruise.

3- I wouldn’t get into carb jetting until you have exhausted all avenues of the 2 points above.

4- Last thing I’d look at would be the oil system, unless it is running near 250 continuously during climb & cruise. Fix 1 & 2 first
 
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"An hour or so with a tube of red RTV can make a big difference."

But, it's soo ugly..... Use clear RTV. Easy to find for this application.
 
I’d suggest first turning the timing advance off, back to fixed timing. If CHT’s return to normal then you know the issue is the timing advance, and you can decide what to do next. Run richer (are you already taking off full rich?), use a higher airspeed on climb to aid cooling, etc.
 
The Surefly should not be advancing the timing at all during takeoff and climb at full power until you reach a altitude where the MAP drops below 25. I would as mentioned try the 23 degree basemap. Changing it however requires removing the Surefly to access the dip switches.
 
Much has been advised. If the surefly was set up for a flat 25*, like the mag, there is a good chance there was an error in setting it's base timing and the increased advance is causing the excess heat.

Before enlarging the jet, go see how far ROP you are. Go to 1000' AGL and WOT with full rich and observe highest EGT. Then lean to peak EGT and stop test/compare EGTs. You shouldn't need more than around 200-250* difference. With my 320, 12.5 GPH is plenty of fuel for 4500 MSL. When I have taken off from Denver, I had to lean a good bit and bet I was around 12, probably less. Probably maxing at 85% power there.

It seems clear that the added CHT is from the advance added with the surefly and 400 at TO is not that bad. If you want better and have a good ROP EGT spread, I would start with remediation of the baffling instead of throwing more fuel at it to cool. With a 25* advance, I can climb well under 400 CHT and I do not climb at full rich. I lean to around 100-150* ROP. Baffling flaws can make significant reductions in cooling efficiency.

Larry
 
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You don't mention the outside air temp when your CHT's are 400+
That makes a difference.
There was a guy on here getting 400+ CHTs on a 75F day. Clearly has big issues. We gave a bunch of advice... and never heard from him again.

But if your CHTs are 400+ on climb out on a 105F day... that's not so unusual. Could certainly be improved, but it doesn't indicate really big issues.

FACTS folks! Give us the data!
And if something helps... help others by sharing what you figured out.

Thank you.
 
Agree you should figure out where your engine is mixture wise first. I would go to 6000 ft and slowly lean off. What is the EGT rise from full rich to max EGT? If it is less than 250F then you are running too lean and a richer jet may well help. If the EGT spread is already 250F then something else is the problem. I would look at baffling, especially the gap at the ends of the ramps at the front of the cowl.
 
The Surefly should not be advancing the timing at all during takeoff and climb at full power until you reach a altitude where the MAP drops below 25.

The OP is probably below a MAP of 25 on takeoff roll or shortly thereafter given his field altitude. Electronic ignitions that start advancing at 25 inches work fine for near sea level operations where the aircraft is well into cruise-climb when it hits 25 inches. For operations from airports at like the OP's (or higher) the start of the advance curve is a bit too aggressive.
 
Thanks for all the input from everyone. I plan to replace my baffles first and look for any air leaks with a light from underneath. Vans sells a baffle material called AirSeal that is a fabric impregnated with rubber on both sides. It is quite thin - probably less than 1/16". This is similar to what is on the plane now. AS sells several baffle materials. I see people using the silicone material which is 3/32" or 1/8" thick. Quite a bit thicker and stiffer than the AirSeal material. Why use one vs the other? Is the 3/32 better than the 1/8 material if I went to the silicone baffling material?
 
The OP is probably below a MAP of 25 on takeoff roll or shortly thereafter given his field altitude. Electronic ignitions that start advancing at 25 inches work fine for near sea level operations where the aircraft is well into cruise-climb when it hits 25 inches. For operations from airports at like the OP's (or higher) the start of the advance curve is a bit too aggressive.

On the Surefly, can you adjust the MAP where the ignition curve comes in? I'm not familiar with them.
 
The OP is probably below a MAP of 25 on takeoff roll or shortly thereafter given his field altitude. Electronic ignitions that start advancing at 25 inches work fine for near sea level operations where the aircraft is well into cruise-climb when it hits 25 inches. For operations from airports at like the OP's (or higher) the start of the advance curve is a bit too aggressive.


I did not think about the DA however the Surefly is also RPM based. If however he is reducing RPM to 2400 or 2500 it is probably advancing the timing at that point.
 
Thanks for all the input from everyone. I plan to replace my baffles first and look for any air leaks with a light from underneath. Vans sells a baffle material called AirSeal that is a fabric impregnated with rubber on both sides. It is quite thin - probably less than 1/16". This is similar to what is on the plane now. AS sells several baffle materials. I see people using the silicone material which is 3/32" or 1/8" thick. Quite a bit thicker and stiffer than the AirSeal material. Why use one vs the other? Is the 3/32 better than the 1/8 material if I went to the silicone baffling material?

In general terms, I find the black stuff to be too flimsy to hold tight against the cowl. The 3/32 silicone has no reinforcement fibers and the 1/8 does. Either will work. I have mitered the corners and glue a patch on the inside of the seal with RTV 732. Without overlaps the seal will sit tight to the cowl and seal very well. Look at the front of the engine for leaks. People often forget to seal there.
 
High CHT's

Probable causes of high CHT's has been talked about for years however there are 2 simple things to check -
Timing - if not set correctly it WILL affect CHT's.
Fuel Flow - should be ~ 14 gals/ hr for -320 engine @ full throttle (sea Level).
If EITHER one of the above is is not correct then nothing else you do will not fix the high CHT's.
Once the above is done then look for other causes.
 
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The Surefly should not be advancing the timing at all during takeoff and climb at full power until you reach a altitude where the MAP drops below 25. I would as mentioned try the 23 degree basemap. Changing it however requires removing the Surefly to access the dip switches.

It’s straightforward to change the timing and advance/fixed without removing the Surefly.
You can access the dip switches with an inspection mirror and a pick.
I literally just did this morning.
 
I have an IO-360 that had high CHTs, reaching 400F just to get to pattern altitude. Fuel flow was 15.9 GPH. I had AFP bump up the flow to 18 and that fixed it. I can climb till the cows come home with CHT well below 400.

When I finish my RV-9 with an IO-320 I will be expecting to see fuel flows no less than 15 GPH.

Probable causes of high CHT's has been talked about for years however there are 2 simple things to check -
Timing - if not set correctly it WILL affect CHT's.
Fuel Flow - should be ~ 14 gals/ hr for -320 engine @ full throttle (sea Level).
If EITHER one of the above is is not correct then nothing else you do will not fix the high CHT's.
Once the above is done then look for other causes.
 
When I finish my RV-9 with an IO-320 I will be expecting to see fuel flows no less than 15 GPH.

That is WAY more fuel than necessary for a 320. There are many other options to keep an engine cool other than throwing excessive fuel at it.
 
That is WAY more fuel than necessary for a 320. There are many other options to keep an engine cool other than throwing excessive fuel at it.

A couple weeks ago I was up to Aero Sport Power to build my IO-320. I witnessed the engine test where they ran my engine for a total of 1 hour 20 minutes in 3 test runs at 2620 rpm and 27". Fuel flow was 16.4 to 16.6 gph. CHT was 310-330F. My RV-6 IO-360 flows 17.5-18.2 gph WOT. Ballpark fuel flow of HP / 10. I'm happy burning some extra fuel to keep CHTs below 400.
 
A couple weeks ago I was up to Aero Sport Power to build my IO-320. I witnessed the engine test where they ran my engine for a total of 1 hour 20 minutes in 3 test runs at 2620 rpm and 27". Fuel flow was 16.4 to 16.6 gph. CHT was 310-330F. My RV-6 IO-360 flows 17.5-18.2 gph WOT. Ballpark fuel flow of HP / 10. I'm happy burning some extra fuel to keep CHTs below 400.

That seems like a lot. My 540 only takes 24-25 GPH 29/2700 and relatively that would be 16 or so for a 360 and 14.5 for a 320. I guess I wasn't thiking of a CS prop that turns 2700. I don't get much over 2500 down low with my FP and why I see mid 13's.
 
A couple weeks ago I was up to Aero Sport Power to build my IO-320. I witnessed the engine test where they ran my engine for a total of 1 hour 20 minutes in 3 test runs at 2620 rpm and 27". Fuel flow was 16.4 to 16.6 gph. CHT was 310-330F. My RV-6 IO-360 flows 17.5-18.2 gph WOT. Ballpark fuel flow of HP / 10. I'm happy burning some extra fuel to keep CHTs below 400.
That seems like a lot. My 540 only takes 24-25 GPH 29/2700 and relatively that would be 16 or so for a 360 and 14.5 for a 320. I guess I wasn't thiking of a CS prop that turns 2700. I don't get much over 2500 down low with my FP and why I see mid 13's.

Here is my 180 HP Lyc IO-360-M1B with the AvStar FI, Hartzell BA CS prop, DA=248', full rich, just after TO. Flows 17.1 GPH +/-. Seems about right per the Lyc charts.

i-pkR2XhV-L.png


The 160 HP Lyc IO-320 operator's manual states rated power, full rich limits as 13.8 to 15.2 GPH.
 
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When I finish my RV-9 with an IO-320 I will be expecting to see fuel flows no less than 15 GPH.

Yikes! I’ve never seen fuel flow that high on my IO320D1A in any circumstance, nor can I recall seeing CHTs higher than 400 degrees.
 
Yikes! I’ve never seen fuel flow that high on my IO320D1A in any circumstance, nor can I recall seeing CHTs higher than 400 degrees.

Me either. That is why I was so surprised when he posted it. Chart in Lyc operators manual for 320 (160 HP) says 14.5 GPH at 29/2700 at SL; Pretty much what I estimated in my post above. They tend to be pretty conservative so not sure why you would throw more fuel at it. THey also say 10 GPH at 75% power and from my experience ROP at 75% power is a closer to 9. I tend to be only 150 ROP on the rich side and never see 400 CHTs down low. Above 8K is a different story, as the ignition keeps advancing and raises CHTs.

Larry
 
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