This is strange,95 temp guage HELP!!!!

My 95 Lumina guage reads hot after only a few minutes idling. I replaced the thermostat, both sensors. No change. I put two external thermometers on the engine and it never gets over 190 deg. The fans don't kick on unless I load up the engine by putting it in gear and hold the brake with a little throttle to get it over 200 deg. I replaced the instrument cluster at the direction of my local Chev. dealer. No change. I replaced the computer at the direction of the Chev. dealer. No change. WHAT THE HELL IS GOING ON HERE. Has anyone ever heard of such a thing like this. No air in system!!!!!!!

You have trapped air in the system. Open the bleeder screws and refill the radiator, let it run for 10 minutes or so, then carefully open the radiator and repeat until no more air comes out of the bleeders.

If you've already done this, you have a wild electrical fault, or a cracked head or etc. Since you are seeing pretty normal temps, and didn't mention it ejecting coolant back to the resevoir or anything, I don't think this applies...

Didn't see the last statement. Sorry. Still sounds like air, though.

Didn't see the last statement. Sorry. Still sounds like air, though.I have tried to bleed this thing ten times and all I get coolant. I have followed the revving instructions and the bypass method. No air.

Don't ever rule out a headgasket problem. I'm helping out a friend with her car. Same issue. It would overheat then cool back down. Everything was replaced like the thermostat, water pump, raditor flushed, ect. with no resolution. I decided to tear apart the engine. This is what the headgasket on cylinders 2,4,6 looked like:

http://www.jdb1941.net/lumina/0228061634.jpg



http://www.jdb1941.net/lumina/0228061634a.jpg



When the car was running, cylinder 2 was acting like an aircompressor to the cooling system. With the engine off and not started for like a day, coolent would leak into cylinder 2 causing it to miss for about 2 minutes during warm-up. I'm quite amazed that the car actually ran like this!

I would suggest to see if your loosing any compression in any of the cylinders. If you are, then you may want to look into getting the headgaskets replaced.

I got you on that but I have no other problems like that. The coolant is perfectly clean and there is no coolant in the oil. I will do a compression check because you are right, you can't rule it out but this is too strange and expensive......................................... .

Aside from a very slight head gasket issue or something of that nature, the only other thing I've seen that is remotely similar is once I had a Caddy in the shop that acted something like that, and after a lot of time spent diagnosing, as something was just odd about the behavior (the clincher was the coolant would stop moving through the radiator even as it was overheating, despite a new thermostat and even REMOVING the thermostat), I pulled the water pump, and found the impeller was no longer solidly pressed on the shaft. At certain RPM it would turn with it, and other times it would stop.

I've also heard of badly degraded water pump impellers not moving enough coolant at idle to keep up, although I've never seen it.

Also I've seen some TSB's about resistors in the temp gauge circuit causing misleading behavior at the gauge, but I couldn't even tell you what cars it applied to...

I got you on that but I have no other problems like that. The coolant is perfectly clean and there is no coolant in the oil. I will do a compression check because you are right, you can't rule it out but this is too strange and expensive......................................... .

Yeah that's why I mentioned the heads too, but generally (but not everytime) you'll see that compression charging of the cooling jacket, it'll eject to the resevoir, or even if not that serious will still produce a steady series of small bubbles at the bleeder, along with hoses that get pressurized before the engine even starts to warm up.

I really appreciate the input and as soon as I get back home (thursday) I'm going to do the comp. check because this is really wierd. Things like these usually turn out to be something simple that I've overlooked but I can't find it.

Thanks

have you tried replacing the temp sensor in the rear head that operates the guage? Your car has two temp sensors. One is in the t-stat housing and is for the computer and the fans. The second is in the rear cylinder head, and has a green wire with an 8" long lead attached. This is the one that operates the guage. Your car being a 95 probably has Dex-Crap, oops, I mean Dex-Cool antifreeze, and it's possible your guage sensor is gunked up with sludge.

Well, on top of both sensors, thermostat, instrument cluster, computer, compression test, spark plug inspection and replacement, and now, just for the hell of it, I replaced a perfectly good water pump with another new water pump. It still goes to 260 deg. in less than 5 minutes while my external temperature guages still don't rise above 195-200 degrees. I'm going to try the raised front end bleeding and a new cap.

I had the same temp problem as you in a 95 Grand Prix with a 3100. Nothing that I did changed the hot running until I replaced the lower intake gasket.
When I pulled the lower intake, it was obvious that there was no sealing in several areas. There was almost no torque on the end bolts when the lower intake was removed.

I feel lucky that no coolant ever made it into the oil either before or after the fix. In the year since I replaced the gasket, the temp has run rock steady at thermostat opening temperature.

The engine does require a special coolant fill procedure. It has two bleeder screws, one by the water pump and the other near the thermostat. As you add coolant, open the screws momentarily to allow air to escape. You would be surprised just how much air can be in there on refill. Never allow the coolant level in the radiator to drop below the bleeder screw level while bleeding because this will allow air back into the system.

I hope this info helps.

When you replaced the guage sensor, did you put teflon tape on the threads? If you did, the sensor isn't grounded and may be mis-reading. The temp sensor is designed to peg the guage if it's not immersed in coolant, and that may be why it's reading so high if there is air in the system. The threads on that sensor are self sealing tapered threads, so no sealant is necessary. Don't listen to the "parts monkeys" that may try to tell you otherwise.

When you replaced the guage sensor, did you put teflon tape on the threads? If you did, the sensor isn't grounded and may be mis-reading. The temp sensor is designed to peg the guage if it's not immersed in coolant, and that may be why it's reading so high if there is air in the system. The threads on that sensor are self sealing tapered threads, so no sealant is necessary. Don't listen to the "parts monkeys" that may try to tell you otherwise.

After everything I have done I decided to buy another temp. switch and install it and that worked. I cannot believe all the B.S. I have been through because I bought a bad in the box part from A.Z. Thank all of you guys for your help and suggestions.