bobbyg21

History first. I have owned this car since it was new. It started mild overheating about 4 years ago. Over the next two years I fought the problem. Been to Pontiac dealer two times and another place once during that time, nobody could pinpoint the problem. Had it flushed first, later had heater core changed after something blew and coolant mist was coming out of vents. Still overheats. Fan appears to come on late ( only after gauge is almost in red ). Changed cap on overflow tank ( no cap is on radiator ). Few months, changed some old hoses that began leaking due to pressure. Later,changed thermostat. Few more months, changed all remaing hoses. Changed water pump and thermostat again while I was there. Week or two later radiator began to develop leaks so I changed it too. Two more weeks something blew in engine and water was in oil. Was told engine was too expensive to repair, it was cheaper to replace. Waited two years, had friend/mechanic replaced engine with used one. Started up, after few minutes of driving, shows that it is overheating and fan comes on just before in the red. All hoses feel hot to touch. No leaks, No smell, but fan continues to run a few minutes after car is off. I would like to not fight through this again. Any ideas appreciated.

gmack221

There isn't really much you haven't changed, verify that the thermostat is put in the right way, make sure the first place you took it didn't put a thermostat in the water neck (drivers side of the head) since it should be under the water pump, try changing the temp sensor (maybe the old one is bad), make sure all of the air is out of the cooling system (run with resivor cap off idling, keeping the fluid level filled, it may boil out before it takes more fluid, don't let it overheat or you'll be replacing the head, have heater on hot & fan running). Thermostat should open at about 210 degrees, fan comes on at 230 degrees (i believe, im pulling from memory here). Make sure overflow tube that comes off water neck to resivor (runs along the back side of motor) isn't corroded shut or something (try using air to see if its open, like a blow nozzel on an air compressor).

Thats all I can think of, the two most likely problems are the thermostat in the water neck & over flow line corroded. good luck and keep us posted, this isn't any easy one!

bobbyg21

Still shows overheating... Okay, thermostat is in right way. Thermostat is located under water pump. The guy that installed the engine for me said he put on the sensor from used engine that I bought. He took out the old "original" sensor from the bad engine because he also thought maybe the sensor was bad. Both sensors seem to work the same. I will change sensor to a new one later if needed. Overflow tube and hose on the back of engine coming from the neck are clear. I ran the engine for a while with the cap off as instructed, it bubbled some air out and kept overflowwing then settled down. After about 15 minutes of that temp was still at 220. i decided to put cap back on and test drive.
Maybe 2-3 miles it decided to start overheating again. I have the standard factory in dash temp gauge and the fan does not come on until temp is almost in the red. I'm guessing around 240 degrees.

Also something else that's wierd... the temperature will not go down by itself easily... but if I quickly rev up the engine ( in park or while driving ) my dash gauge shows the temp going down about 60-100 degrees. 2-3 more miles it creeps back up. Maybe I need to check flow in radiator or engine? It has a crazy set-up, do you know how check flow? Is it possible that the temp gauge is wrong and the car is not overheating? How can I check the temperature? Anymore suggestions are appreciated. Thanks

skibum1111

Something in the cooling is blocked. Did you change your heater hoses? The junction block in the middle of the hoses is a bypass as the heater core can't handle the coolant flow when the motor is above 1500 rpm. When you rev it past 3000 rpm the pressure from the water pump forces the thermostat open, thus allowing the motor to cool off. Do a flow test with a garden hose, see if you have good flow through the heater core and the bypass. If its slow, disconnect the heater core, run water through that with the hose, if its faster than before, replace the heater hose assembly. Also do a simple flow test on the radiator. Pull it, put it in the bathtub, it should keep up easily with the water coming out of the spout without backing up. Good luck.

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gse2schmidt

Sounds exactly like my post a year ago. The problem I had is that if the engine had no load it would stay fairly cool. Like idleing in the driveway. I had bubbles in the coolant coming from the rear vent line constantly. Once I drove it around the block a couple times.....or dared to get on the freeway....watch out! It would vaporize coolant.

Bypassed the heater core, replaced the radiator and thermostat. Also verifed that the water pump was turning by looking thru the weephole on the bottom side of the pump. Verified water pump impeller was in good shape by looking up the coolant return line on bottom side of engine.(It's possible for the water pump splines to wear out and cause the pump not to turn). If your not sure, next time you go to the auto parts store ask to see a water pump for your car. Saw the same thing with the free rev rpm dropping the temp a little at a time, but not enough....remember it won't take the load.

Did read one article were someone had the coolant vent tube that runs above the exaust plug and once he got flow it got rid of a huge air bubble in the top of the engine. I disconnected mine from the return tank and dicovered that it was blowing combustion gasses and coolant just fine...no blockage there.

Final answer was.....blown head gasket. My mechanic happened to have a head off of another 95 quad 4, that ready for this.....had a blown head gasket. They were not so lucky and put a new head on, but coolant had gotten into the oil and in a hundred miles the bottom end of the engine failed.
So I used the 100 mile head because he only wanted $100 for it. The cooling system in the car was spotless, except when they went to pull the head the coolant passages in the head were heavily eroded away at the gasket surface. I'm sure a head resurface might have cleared things up, but it was overheated by a previous mechanic several times and I didn't want to risk a cracked head. My 16year old has put 20K on it since then it seems to loose a little coolant now and then but all and all a sucessful repair(knock on wood).

My mechanic says that once the headgasket is replaced successfully that usually they hold. I think a big problem is that some STUPID PENCIL PUSHING CUBICLE ATTENDANT at GM thought that waiting to turn on the cooling fan around 230 DegF was a good Idea.....what trying to save electricity? Cast Iron blocks and aluminum heads expand differently, especially the higher they are heated.....Duh.

I've been thinking about adding a second aftermarket temp switch relay control to the cooling fan and running it along with the existing system.

Call around, several mechanics refuse to work on these engines. Some just bid high to scare people away. I got prices from $1800 gasket only to the guy that replaced the head and gasket for $600.

Don't go with the GM gasket....they work so well....NOT. Actually the new and improved GM gasket works fairly well but is pricey and we want to reward GM with our hard earned money for not getting it right the first time....Right! Felpro sells their gasket along with head bolts(a must) for around $100.

Let me know how it goes.