My 61 Comanche 250 carburated CHT on the number 5 cylinder, I believe it is the one on the rear co pilot side, has always run a good bit hotter than the others. In the climb it is usually in the 380-390 range. In cruise it is usually 350-360. In both cases it is running 30-40 degrees hotter than the others. I have checked the baffling and everything apears like it should be. Just wondering if anyone else has experienced this or any suggestions on how to get a cylinder to run cooler. In the climb I watch it and adjust my pitch as necessary. I have tried leaving the boost pump on but does not seem to make much difference. I have been running 50-100 ROP.

Thanks

Mark

Content Deleted

David, thanks that is good to know. I guess I was just obsessing about it. I have only had my Comanche for about 3 years. Just when I think I know everything there is to know , I find out how much I don't know!

Thanks

Mark

Mark, you have a lot to look forward to - 42 years around the same aircraft and I'm still learning.

P.S. David is modest - he won't tell you his gorgeous Comanche won the Flagship a few years back and he has every piece of paper ever written about that plane in perfectly organized matching binders .... I'm envious.

Hi Mark,

One thing you did not mention is whether you have checked the seal that is between cowl and the front of the engine. This seal is virtually invisible with the cowl installed. We bought our Comanche with a new engine, and new baffling on the top of the engine, but the shop doing the install failed to replace that seal which had rotted away. We also had to restrict our rate of climb to keep #5 below 400. Mentioned this to my mechanic, he replaced the missing seal, and since then I have not seen an cht reading above 360,in climb, no matter the temp.

Good luck, Don

Don, thanks, is this seal on the top or bottom, what color, do I need to take the cowl off to look for it ?

Thanks

Mark

The seal is made of gray felt, 1/2" in thickness, and can be seen and felt at the inside lip of the cowl opening. It is stapled to the front of the metal baffles on the engine. The cowl will need to be pulled to replace the seal if that is needed.

Don

Don,

Thanks. I bought some new baffles a couple of months ago because mine were cracking. At the time my shop just repaired them because I had to wait for the new ones to be made. I will go ahead and install them. I ordered some new chafing strips also. I will see if it makes a difference and report back!

Thanks

Mark

Hi Mark,

Curious to know if you are running a JPI Engine monitor to measure the CHT, the reason I ask is I just installed a JPI EDM 700 in my 66 260B and the probe for number 5 CHT had to installed on the top spark plug as per the install instructions as the factory CHT is taken from the normal probe port on the bottom of number 5 cylinder. The JPI manual did mention that there is a risk that the the CHT may indicate 20 to 50 degrees differential from the other cylinders as we installed the probes in the normal probe ports on the bottom of the other cylinders. I find in cruise running 20 degrees rich of peak on the EGT the cylinder runs a linear track on the JPI approximately 40 degress hotter than the other cylinders. (345 versus 385)

Regards

Bill, yes I am using a JPI 930. I think all of my probes are on the top of the cylinders. I just had them all replaced at the annual last month because the shop that installed them originally had them at all at different depths and I was getting temperatures all over the place. They do run a lot more even now. I will take a look tomorrow and let you know. You have got my curiosity up.

Thanks

Mark