Overheating Issues

1992 SC, 112k miles

In November, 2004, blew the head gaskets. Replaced them, machined heads, then car sat for 3 month under 10 foot of snow.

Started driving and the DIS module went south. Now the brake ABS relay took a permanent vacation. All fixed.

Here is the problem. Car overheats at highway speeds..that is, temp climbs up to within 10% of red. Around town, runs at 25% from red. With A/C on, stays at 50% until on the freeway, then climbs right up to the 10% mark.

Had no low speed signal from the IRCM, so bought a used one...it now has signal but still no low speed fan. Have just ordered a new fan from NAPA. (High speed works fine)

Well...sorta...once it comes on, it doesn't like to shut off until the ignition is killed, then it goes off and won't come back on until temp hits 222 or there-a-bouts.

Question here is: This car never had a heating issue until the head gaskets blew. None...ran at 50% all day and all night, summer or winter.

Nothing but grief since the gasket replacement. Dealer is reluctant to look into the possibility that wrong gaskets were used or they were put on upside down. Their techs would never do that....RIGHT.....

What can I possibly look at as a reason for the overheating or high temp running issue? (Oh yeah.....radiator is good....not blocked)

Thanks in advance!

MC

I would start by getting all your fan gremilns taken care of. I assume they put a new thermostat in when they did the head gaskets? I would also check your temp sensor, near the thermostat as it can cuase problems also.

Thomas

Thomas A said:

I would start by getting all your fan gremilns taken care of. I assume they put a new thermostat in when they did the head gaskets? I would also check your temp sensor, near the thermostat as it can cuase problems also.

Thomas

Click to expand...

Yes, new Thermostat, and both sensor's...guage and 'computer'.

Engine coolant temp verified with an electronic (Infared??)temp reader. Gauge is mostly accurate.

yeah mines is the same thing.... i think its the fact that now it has a thermostat... maybe i should take it out? but yeah i dont like it...

It's very strange that it's almost in the red at highway speeds. Mine sits barely above the "C" at 55 or above. I have 2 suggestions:

1. Is something blocking the airflow to your radiator? There is a lot of air blowing past at 55 mph ... I would expect it to be more than adequate to cool this engine.

2. If it really is too hot, I would guess that something is wrong with your thermostat. Either it's broken, installed backwards, or the mechanic used the wrong thermostat. The non-SC 3.8L thermostat looks similar, but lacks a bypass hole that the SC one has.

I hope you find the problem!

Here's something to check...

Make sure the air deflector is still installed on the underside of the front bumper cover. It's a little black plastic piece about 2' long and about 2" wide. At highway speeds (actually above 45mph) the cooling fans kick off and the radiator gets forced air from this deflector. If it isn't there, you aren't getting enough air through the radiator vanes at higher speeds. I lost mine a while back and the old bird would run way too warm while cruising, but cooled down in traffic, just the opposite of what you would expect. I replaced it with a deflector from a "late model" Pontiac Grand Am GT, which is longer and wider than the original SC unit. It required a little modification to mount it, but it solved the problem.