The International Cessna^® 170 Association

I would like to add a EGT and maybe also a CHT to my O-300-C.
What cylinder should the probe go on?
Does it matter?

I believe you want CHT on the hottest cylinder, and EGT on the one that peaks first during leaning.

My O-300 has EGT and CHT on all cylinders. I observe that #2 cylinder is always the hottest, and I think that's generally expected.

When leaning, I believe it's #5 EGT that peaks first (although it's been a long time since I've tried to use peak EGT for leaning, and my memory may be faulty). I've gone back to leaning by the method described in the owner's manual, and using EGT and fuel flow just for fine-tuning.

Others may weigh in with what they see, and then you can decide.

The NO. 2 cylinder is the one chosen by Cessna for both probes.