High CHT...

[kklewin]

Quick question for the A and P crowd....been flying my 6A for 3 year or so...about 170 hours on an Aerosport O-360-A2A...my CHTs were higher initially (on all cylinders) ...up to 450 in climb...about 390 in cruise....I added the vents to the bottom of the cowl and they dropped significantly to 350-380.....lately (last 5 hours or so) my #3 CHT is much higher (up to 100 deg higher) in climb and about 80 higher in cruise. Cruise is about 330-350 on 1,2,and 4 with #3 at about 435-440. Aerosport says its most likely a baffel issue. I just did the conditional and compression is good on the cylinder and the baffeling is still in great shape...any ideas?

Kurt in OKC

[Bob Martin]

Kurt,
I'm not an A&P but have been working on cooling issues as well on my -6.

Lycoming cylinders have a good amount of cooling fins on the exhaust side of the head and a lot less on the intake side.
The #3 cylinder is the only one that puts the intake side against a flat baffel.
therefore, it has been suggested you install a couple fat washers between your baffling and the cylinder head on the mounting screw to get more airflow to help with cooling the #3 jug. I think I have about 1/8" gap.
Also, where is your oil cooler? original plans showed it firewall mounted behind the #3 cylinder with a 3 inch scat hose. Newer plans plans show it mounted behind #4 on the baffeling itself. The original location robbed air from the #3 cylinder for sure. Seems there is plenty of air on the #4 side.
I also had high CHTs on Takeoff but lowered them by rejetting the carb to get more fuel flow at WOT. I used info from AVWeb, John Deakin's articles called Pelicans Perch. Look for #64-"Where Should I run my engine"
Read the whole article but he says the TO egt should be 1300degrees and if it is higher, add more fuel. This is general info for normal airplanes assuming good baffeling and proper functioning equipment, etc etc. It worked for me.
Just some ideas, hope it helps.

[kklewin]

My oil cooler is on the fire wall with a 3 in scat coming from behind the #4 cyl. It seems to work great.

Thanks for the great suggestions, seems #3 is always a problem....

Kurt

[Bob Martin]

Kurt,
One more item to check, this happened to but it was awhile ago.
Do you have the bayonet style probes on all your cyl's?
JPI would send one under the sparkplug type probe with there units to as not to disturb the TSO'd installations. I guess this was before the EXPERMENTAL's got so popular. Anyway, the under the plug probe reads 50 to 100 off from the others and the #3 cylinder is where most certified cht probes are located, so I thought it was worth mentioning.
Again, my RV-6 was set up this way when I bought it and it took some research to find the problem and fix it. For me it was as simple as changing a probe.
Good Luck.

[kentb]

I thought that I had a misreading CHT on #2. Rob Hickman suggested that I just swap the #2 and #4 probes to see if the problem would change cylinders. It didn't solve my problem, but it is easy to do and might help eliminate one source of error.

Kent

[rich]

Kurt,
Check the torque on the intake manifold bolts.They will loosen up after time causing a cyl to run lean and hot .
One RV at Hicks had #4 cyl start running hot all of a sudden.
Turned out to be the Intake Gasket.
Hope this helps.
Rich
RV-6A
750HRS