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gereed75

Well Known Member
I went out today to check something out that I was curious about - Does the airflow taken off of #4 cylinder for oil cooling effect CHT??

I have a flapper door that completely closes off the flow to the oil cooler in my duct behind #4 cylinder. I set up at a 24/24 cruise and opened the door all the way until oil temp and CHT stabilized. Then I closed the door all the way and stabilized again. Oil temp went from 178 to 187 after a few minutes - No change in CHT's at all.

For anyone who is curious, taking the air from behind #4 does not seem to effect #4 (or any other) CHT, at least on my set-up with a stock inlets to a sealed plenum.
 
My experience is similar

I have a stock cowl. I have a 3.5" scat tube coming off a flange on the back of the #4 cylinder baffle, which goes through a butterfly valve, then runs to the firewall-mounted oil cooler.

I have found no effect on CHT on any cylinder by throttling the air through the cooler. There is apparently enough stagnation in the upper cowl plenum to effectively equilibrate the pressures and flow through all the cylinders, and apparently enough excess intake capability to make up for the increased flow through the cooler.
Both my front cylinders run slightly hotter than both of my back cylinders. (front deflectors have been cut down some, need more)
 
same with my 4" line

I sure thought that it would effect the flow in some way but I have the same experience of no impact on CHT from oil cooler airflow.

What cylinder is your coolest CHT?

My #4 cylinder is the coolest by about 25 degrees from #2 in cruise. I suspect that the dynamics of airflow within the cowling are unique and somewhat unpredictable... I did remove the deflector plate on 2 to help balance the pair and it brought the spread down from 40 but I am out of ideas on bringing the temp up farther... probably doesn't much matter though.
 
Shoot, this is disappointing to hear. I just recently installed an oil cooler buttery fly door, after vacillating over whether i wanted an additional control to deal with for months. I have not yet tested to see whether it stabilized my CHTs.

I have screenshot after screenshot with the following CHTs spread. CHT1,3,5 all consistently lower than CHT2,4,6 (odd vs even or left vs right). CHT1 and 2 have airdams cutdown slightly arbitrarily from stock. Instead of blindly trimming, I decided to got more engine temp data.

Oil cooler inlet is on the left side creating higher CHT2,4,6 i assumed.

screenshot-20120304-160859-554.jpg
 
Kinda makes you wonder about plenum religion doesn't it

An old friend of mine (since nobody's observation seems to count without credentials - back at MAIR President Robert Little called it technical arrogance - he graduated as a mechanical engineer from the University of Arkansas and received his masters degree from SMU and specialized as a thermal engineer on the F8U) told me the velocity of the air flowing though the oil cooler is not very high. On the other hand covering the large wide open port for the heater air (which on our plane is dumped overboard through the small zone 3 vent when not used) and the two mag blast tube ports does reduce the CHT on #3 and allows the plane to fly a little (not a lot) faster.

Bob Axsom
 
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