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Do I have a CHT problem?

carrollcw

Well Known Member
Here is a pic from my recent test flight (post injector tuning):

Post%20Tuning%20Climb.png


As you can see, my EGT's are very tight and peak together, but I have a pretty large CHT spread (approx 55 deg) between cylinders 1 (coolest) and 2 (hottest). What gets my attention is the fact that the spread exists during all conditions (idle, climb, ROP, LOP). Would this be an indicator of a separate issue besides baffle? If it was a baffle issue, I would think that the temps would be fairly tight on the ground and then diverge once flying, but that isn't the case. Any ideas?
 
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1. Did you put the washer between cylinder #3 and the rear baffle?
2. Have you cut down the air dam in front of #2?
3. Based on fuel flows, and recent OAT, it would appear the CHTs are a bit elevated. Leaned out and in the summer might be a bit toasty.


Good job on the EGT. They are all peaking at the same tim3, which is more important than value. You seem to have both.
 
1. Did you put the washer between cylinder #3 and the rear baffle?
2. Have you cut down the air dam in front of #2?
3. Based on fuel flows, and recent OAT, it would appear the CHTs are a bit elevated. Leaned out and in the summer might be a bit toasty.


Good job on the EGT. They are all peaking at the same tim3, which is more important than value. You seem to have both.

1 - Yes
2 - Yes
3 - I am actually running fairly rich in order to keep #2 cool enough (I have an O2 sensor installed). That is my concern. I am trying to get #2 cooler, but I think this might not be a baffle issue.

Re the EGT peaking at the same time, that is the result of the fact I have individually tunable injectors. There is a VAF thread about it ("My GAMI spread is Zero"). Amazing technology!
 
What is your power setting in the above flight? 16.6 GPH is a LOT of fuel and EGTs of 1100 are extremely low. (yes, I know absolute numbers can be misleading) . What do the spreads look like with a normal cruise setting?
 
What is your power setting in the above flight? 16.6 GPH is a LOT of fuel and EGTs of 1100 are extremely low. (yes, I know absolute numbers can be misleading) . What do the spreads look like with a normal cruise setting?

WOT and the snapshot is at 1500'. I agree, I don't think the EGT's should be so low with the CHT's so high. That fact combined with my O2 sensor info lead me to believe I am running really rich.

EGT's go up to about 1250 when running LOP and hottest CHT at about 360. I never cruise ROP.
 
How many hours are on the engine?
How far from the cylinder are the EGT probes located?

I always run ROP. I have ran LOP a time or two. When I did, CHT was much lower than when running ROP.
 
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How many hours are on the engine?
How far from the cylinder are the EGT probes located?

I always run ROP. I have ran LOP a time or two. When I did, CHT was much lower than when running ROP.

About 120 hours, they are all evenly spaced - I think they were at 2" away.

Due to the tuning of my injectors, I can run anywhere from barelyLOP to 200 deg LOP. At 30 deg LOP, I am close to 380 deg CHT, obviously as I get leaner I get way cooler.
 
You stated that you had a washer under the #3 baffle, did you put one on the number two cylinder?
Also, try a bit of metal tape on the front of #1 to raise the temp here, this may allow more air for the other cylinders.
 
There are more effective methods to deal with #2 and #3 cooling than the "washer trick" if you find that indication is accurate. Plenty of threads ot the subject.
 
Micheal is correct, there are some very nice, and even, elegant examples of how cooling can be increased around the back of #3 and the front of #2. With the baffles installed as per plan there is definitely a blockage of air on those cylinders.
But before going to the work of taking the baffles all the way, and making those mods, try a washer, or better yet a spacer about 2" long by 3/4" to see if this does improve cooling on that cylinder.

As has been stated before, cooling issues are rarely one particular problem and need to be addressed as a cooling system problem, starting at the inlets and ending at the cooling air outlet.
 
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I guess I'll test the cht probes before I do anything else. Busy w family stuff for a few days so I'll post results when I get to it. Thanks for the ideas!
 
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