After installing headers on my 81 it runs much hotter than before. I have a few small leaks on the front y-pipe, and the O2 sensor is farther back than it was before. Could either of these be causing this, or is there something else?

 

Ben,
I assume that you've got Headers connected into the stock system? Last winter I put some Dynomax Headers on mine & replaced the MA duals with some that I made myself. The O2 sensor is located in the reducer on the d.side, which is further back than with the stock system. I also fitted a 200-4r & a transmission cooler at the same time & the engine now runs cooler than it did before. Without the trans cooler the trans fluid was getting too hot, but the engine coolant was still colder than it used to be, so I don't think the tranny cooler has much to do with it. What I put it down to was that either the torque converter was now locking up OK (my old TH350C converter lockup stopped working, generating more tranny heat & higher engine revs) or that the exhaust was scavenging more efficiently. Either way, my engine now runs cooler.
Are your Headers wrapped or ceramic coated? I'm convinced that my engine bay temps are now lower than they used to be, probably due to the ceramic coating on the Headers.
How bad are the exhaust leaks? I know for a fact that an exhaust leak at the manifold will generate a lot of heat & can cook an engine (something I'd rather not remember!) but leaks further down the system have never caused me overheating problems.
I can't remember what temp sender does what on the L81, but could the Headers be locally heating one of the temp sensors, cdausing it to give false readings???
:cheers:

 

I found that to be true for the temp sender for my electric fans. Moved the sender to the intake manifold and all is well.

 

When you change to headers, you should also check/adjust fuel mixture as you may be running lean, which will cause your engine to run hotter than before.

 

I have the ceramic coated Dynomax headers and I've put the O2 sensor on the reducer. When it is 80 degrees or below outside the temperature is right where it's supposed to be. It only overheats when it's 90 degrees or hotter, or when I am going up long hills. I thought that the fuel mixture could not be changed on an 81, because it is controlled by the computer.


[Modified by Ben Taylor, 9:08 AM 8/19/2003]

 

Ben,
It sounds like the same setup I've got. We've lately had temps in the 90's (even went over 100 on one day!!!) & my coolant never hit 200F on the gauge. The only temp I could get to go higher was the transmission fluid. What temp is your's getting up to??
The mixture on the primaries should be OK as the computer controls it, but the secondaries are no different to non-computer Q-jets. I suspect that mine may be running a bit lean (only because every vehicle I've opened exhaust systems up on has needed a richer mixture at the top end), but finding the parts to do it in the UK isn't easy.
The coolant temp on mine sits reliably at the mark between 100 & 200 on the gauge. I thought that mark was 150 but somebody told me it was 180 (I hope it is!). I've also got a 180 stat & a re-cored rad. The stat didn't seem to have much effect on the temp, but the re-cored rad had a big effect when I did it last year.
:cheers:

 

The coolant temp is about 230-250 but I think it would go even higher if I left the A/C on. The oil temp is usually between 250 and the mark above it, which I think is 285. This is during temperatures from 90-100 outside.

This morning though, when it was about 80, my coolant stayed at 180, and my oil temp stayed on the mark between 100 and 250, which I believe is 200. It didn't matter if I was on the freeway or in stop and go traffic.