Okay, i have a 22re, built it 2 years ago and i have around 15k on it. its been running warmer than i feel it should, bored .040 over with a 268 cam and O/S valves. its got a 3 core rad, electric fan that is set to come on at 200, off at 180, 160 t-stat, plus an oil cooler, yet it still runs around 200, it can get up to 210 or so in the hotter months. i do have an aftermarket gauge so i get fairly accurate readings. no external leaks from hoses or anything, so i did a compression check and came up with 180 for cyl. 1,2,3 but cyl 4 was 150. i checked the valve clearance and tightened it up a little, to around a slightly tight .007. that made the compression worse, like around 125. could this be related to the cooling problem im having? its running a little rough with some hesitation, but i do have an exhaust leak and i know the 02 sensor needs replaced. ill do a leakdown test on monday, but anyone have any thoughts or experience on an issue like this? thanks in advance for any responses.

anyone?

How do you know the O2 is bad? If you are sure it's bad, start there. There is no point in further attempts to diagnose a system with a known problem.

I'd also try to get back to the earlier compression numbers...

Cooling system:
Are you losing water?
When the truck gets hot, does it get hot sitting or does it get hot under load / at cruise?


Your compression is OK, other than that one cylinder. IF you're not losing water, I wouldn't worry about it too much - normal for tight valves to impact compression, btw.

Leakdown test will confirm possible head gasket issue on the low cylinder - but you'd normally overflow or lose water.

curious --- why do you have a 160 T-stat in it? Why not a 195? Have you tried a 190 or 195 t-stat? If so what happened?
Did you get the leakdown test done? As above I'd like to know if it's using coolant...

oh yea.. where's the specific location of the exhaust leak?