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O-320 cylinders 2&4 run hot.

pylotttt

Active Member
My RV-6a O-320 cylinders 2 & 4 run hot.
I have changed the baffle material and sealed leaks, replaced Bendix mags with p-mags, new plugs, wires, etc.
Both p-mags are timed the same.
If I run on the right p-mag only, the temps all come down and are close in temp below 370 degrees.
If I run on both p-mags or the left one the temps will increase on #2 & #4 going over 400 degrees unless I keep the RPM under 2400.

My oil cooler is mounted on the baffle behind #4. I currently do not have the oil cooler shutter but need to install one before winter. Even with 97 degree days my oil temp is around 188 degrees.
I'm wondering if I am dumping too much air through the oil cooler and not enough pressure differential to properly force air through #2 & #4 fins.
This still doesn't explain for the temp discrepancies on the left as opposed to the right p-mag.
I am going to try to put a forward angled piece of metal at the rear fins of 2 & 4 and see if that helps.

Has anybody had an issue with the baffle mounted oil cooler causing the cylinders in front of it to run higher?
https://photos.google.com/photo/AF1QipOJ4ZjUjBNKDe5haPUzfS3yZVd_lZs-IX8qUCRT
https://photos.google.com/photo/AF1QipMDzP7V7noYiaH_tacwMn24QBxAhPcIxCzH8Vwz

Thanks for any feedback.
 
Rob your pictures didn't show up. There is a how-to insert pictures tab in the upper left corner of this page.
 
I tried that but they didn't show up so I removed the IMG tags so people could click the link to see them.
 
My RV-6a O-320 cylinders 2 & 4 run hot.
I have changed the baffle material and sealed leaks, replaced Bendix mags with p-mags, new plugs, wires, etc.
Both p-mags are timed the same.
If I run on the right p-mag only, the temps all come down and are close in temp below 370 degrees.
If I run on both p-mags or the left one the temps will increase on #2 & #4 going over 400 degrees unless I keep the RPM under 2400.

If the left one causes higher CHT, then it is not timed the same.

My oil cooler is mounted on the baffle behind #4. I currently do not have the oil cooler shutter but need to install one before winter. Even with 97 degree days my oil temp is around 188 degrees.
I'm wondering if I am dumping too much air through the oil cooler and not enough pressure differential to properly force air through #2 & #4 fins.

I have run tests, and they indicated the oil cooler may affect all CHT's but not just one side. So - No factor for you.


This still doesn't explain for the temp discrepancies on the left as opposed to the right p-mag.
I am going to try to put a forward angled piece of metal at the rear fins of 2 & 4 and see if that helps.

Has anybody had an issue with the baffle mounted oil cooler causing the cylinders in front of it to run higher?
https://photos.google.com/photo/AF1QipOJ4ZjUjBNKDe5haPUzfS3yZVd_lZs-IX8qUCRT
https://photos.google.com/photo/AF1QipMDzP7V7noYiaH_tacwMn24QBxAhPcIxCzH8Vwz

Thanks for any feedback.

A few findings (mine)
A. #2 and #3 have specific issues that can increase the temps.
B. Adding shields to the front two cylinders can increase them and allow more air for the aft cylinders.
C. Mixture imbalance between cylinders can affect them at full power. Esp a carburetor.
D. When all else is done the open gap below the head can affect a single CHT.

As noted above one mag seems to be advanced relative to the other as evidenced by the CHT effect.

If you can provide some engine flight data it would be quite helpful. Savvy can be used for free.

Balanced temps is a juggle of a number of variables, but certainly can be done. Seldom quickly.
 
What about the other ones?

What temps are #1 and #3 running?
Do you have the deflector installed on the front of #1?

Helped a guy with similar issues... adding a deflector on #1 raised #1 by a bit, but helped cool all of the other ones.

Check for flash in the fins on all cylinder heads.

Gaps, gaps, gaps. Front corners are a classic spot to have baffle issues.
Same guy, we just found a 1" x 3/4" hole at the back of the #3 jug base. That lets a lot of air pressure out uselessly.
 
Is this a new problem, or has it always run hot?

Have you verified the plug wires run to the correct plugs?
 
OP’s photo links give me Error 404.

This RV at SunNFun 2021 fixed a left/right cooling issue with a center baffle. IIRC the owner doesn’t know why it works. Sorry I didn’t get the tail number. Nor do I recall which side was hot. I’m not saying it’s a the best solution in your case, just FYI.
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Antisplat cowl flap

Not saying you don't have an issue with high temps on one side that needs to be addressed, but I really like my Antisplat cowl flap. I installed one on my 6A and get at least 5 degrees F of benefit when I open it. Installation was easy. John
 
I have the same issue with #4 running hot, I also had lower than optimal oil temps. I blocked off about 1/3 on the oil cooler and this did help bring the oil temp up a few degrees and also lower the #4 CHT a few degrees. It didnt solve the problem, but it helped.
 
PMag

I am drawn back to your initial statement that the engine seems to perform well on the right mag but on both or just the left it over heats cylinders 2&4. There may be improvements to the baffling but it seems the issue really is with the left mag.

1. You mentioned both mags timing was checked. It might be worth rechecking. I test flew an aircraft that had been timed incorrectly (PMag) and it performed just as you described. On both Mags temp went hot, turn off the incorrectly timed PMag and the temps quickly returned to normal.

2. Are you running the same curve on both mags (A versus B?) If it’s A any possibility the jumper was accidentally dislodged from its connector during timing/maintenance? The net effect would be different advances for each mag.

3. Occasionally PMags fail, have you considered sending the left one to Emag?
 
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