My friend's got a 92 RS 3.1 MPFI. His car has had some overheating problems and the heater only blows out cold air. We checked the water pump, and it's still working(not leaking coolant through the seep-hole), so were pretty sure that it's the t-stat. When I'm saying the car running hot, I mean like 220-230 in 30-40 degree weather! I keep telling him to replace the t-stat or he will pay later, but he thinks its no big deal, and doesn't feel like replacing it(on the RS, you have to take the plenum off). Please put some posts on here to convince him to put in the new stat.

By the way- I'm runnin a 85 Z28 305 w/gutted cat, holly preformance carb rebuild, port/polish manifold

 

when do these temps happen? during the highway or in traffic?

might just need a proper flush and a 50/50 mixture of coolant and water.

changing t-stats isnt a bad idea but sometimes may not be the problem.

could be the airdam not being there, or fan not working either.

 

bad (HCV) heater control valve + air pocket = overheating.

changing out the t-stat wouldn't hurt anything. i say change it out.

 

you don't have to take the upper plenum off, you just have to have a swivel socket. i changed those out all the time on my old 2.8 (same intake). go get a swivel socket from sears for a couple of dollars. you will be able to use it on other stuff later too.

 

The first think to do is to check the air dam. Mine was missing, but it didn't let the engine get THAT hot in the winter... Drain the system then check the stat and heater control valve. If both are good then check for vacuum at the hcv and if you get none, check and replace the line leading to it if needed. The HCV is $16 and the stat is like $8, so I think that your friend can afford both if needed.
FLUSH THE SYSTEM!
Then, refill the radiator to the top, turn on the engine (without putting the rad cap back on) and the heater, and add coolant mix until the coolant level stays at the bottom of the cap mount, then put the cap back on.

 

I wouldn't worry about it too much. When it finally really overheats and warps the heads, the intake will have to come off anyway... Until then, your friend can drive around in complete bliss, with no heat, and a soon-to-be-lighter pocketbook.

 

A thermostat costs $3 and takes 10 minutes to change. How could you NOT justify changing it regularly?

It won't help with the "no heat" problem (that's a plugged heater core or stuck coolant diverter valve) but it might help with the engine overheating problem.