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My Son's Grand Am suddenly overheated to the point the engine shut off. After allowing it to cool down I inspected it and found that the previous owner had improperly installed a new thermostat. The thermostat had slipped out of position when it was being installed which caused the housing to not seat properly and the housing pinched the thermostat seal and the lower housing bolt wasn't tightened enough so when the gasket gave way all the antifreeze was pumped out. I replaced the thermostat and replaced the antifreeze and took it for a drive. It overheated again and dumped most the coolant out again. After trouble shooting some more I discovered that the fans were not working, it has new fans, so I checked the relay and fuses, everything was good except I did notice that someone had removed the air condition clutch relay so I replaced it. I refilled it again. I started it and allowed the engine to reach the normal operating temperature. The fans starting operating and it seemed to be staying at the normal temperature . I took it for another drive in town so that I could go at least 50mph and up hills, about 8 miles, everything seemed ok. I stopped at a store and shut it off. When I came back it had dump the coolant out of the coolant tank through the overflow. By the time I got it back home the temperature had gone to the max again. I thought the water pump was making a noise so I replaced it also. I checked the old pump out and it seemed to be ok. I checked the oil to see if it had any coolant in it and it didn't. Does anyone have an idea why it runs ok and then after shutting it off it overheats and dumps coolant out the overflow?


   
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It's really bad to run an engine when the temperature gets into the red on the gauge. Of course, it's much worse if you run it in the red until you kill the engine. You may have blown the head gasket. If the previous owner replaced the thermostat, there may have been overheating problems form before you bought the car.

You can put a radiator pressure tester and measure the pressure build up when you start the engine. You put the pressure tester on the radiator where the cap goes on. You don't pump the pressure up like looking for a leak but just leave it at zero. Then go and start the engine. let it run for a short time then rev the engine up a couple of times. Just goose the throttle a couple of time getting the rpms up over 3-4k. If the pressure jumps up pretty quickly, the engine is putting pressure into your cooling system.

Another way to check for a blown head gasket is to use an exhaust gas analyzer and check to see if you have hydrocarbons out of the cooling system. there is also a chemical test that can be done to look for hydrocarbons out of the cooling system.

of course, there is also the possibility that you have a bad cap. Everyone knows that water boils at 212F but cars run at temperatures all the way up to 240f. Antifreeze in one thing they use to raise the temperature without boiling. Another thing they use is pressure in the cooling system. Keeping the pressure in the cooling system helps keep the coolant from boiling. Most cooling systems have a radiator cap that hold pressure in the cooling system. Your cap should hold 15 lbs. If you have a bad cap it may not hold the pressure in and the system will push the coolant out into the overflow bottle. It would be very lucky if that's all that was wrong with your car now though.

In my shop we have a sign that says that if your car overheats, even one, time you may have damaged your head gaskets. It may not show up right away. over time you could be loosing coolant without noticing any leak externally. You could have a rough running engine when you first start the engine up. It may get worse over time...


   
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Don't know when this question was asked,but the first thing to check is the pressure cap. That is a very common problem after a boil over in these cars. It's seems there only good for one boil over. U should replace pressure cap after a car gets hot anyway. Next step filler up and pressure test if pressure falls find the leak. Take spark plugs out so it does hydrolock.if nothing running on the floor spin motor over with plugs out and look for antifreeze. Then check oil.water in either, blown head gasket or cracked head or leaky intake gasket.


   
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Sounds like you have a crack in the head or cylinder wall of your block. If it over heated to severely the head is warped and unless you buy need head and head gasket your going to have to have head shaved by a shop. Have it checked for hair line cracks. Inspect cylinder walls as well if you intend on rebuilding motor. Done a lot of that family of motors from the old 2.8 to the 3400. All the same when they blow


   
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The problem is related to the computer sending a ground signal to the cooling fans. I just fixed my daughter's 2003 Grand Am GT. The problem is what looks like a relay mounted to the driver's side fender wall. It's located directly across from the air filter assembly. Pontiac has located this device there and all your major grounds join here. The mounting plate attached to it becomes corroded which interferes with the grounding signal from the computer to turn on the cooling fans. The bolt that held it in place was actually so rusty that the head of the bolt had broken off as I removed it. I used a circular wire brush attached to my drill to remove the corrosion from the back plate. Used the same brush to create a new bare metal spot on the fender and a self taping screw to reattach it. No more over heating from there on, Fans triggered and varied speed as they should. Also check that the O-ring on the coolant reservoir is in tact, hers had broken in half and was lying on the inner fender. The cap would not unscrew properly and that's how I found that issue. It keeps air from being sucked into the system.

This ground block can also affect other operations the computer performs such as dash gauges etc... The computer must have a solid grounding system. Sadly, you've wasted a lot of part money but, so did I until I figured out the real issue. My electronics training ended up solving the issue.

I've also had similar issues in a 2001 Chrysler Town and Country with grounding issues. A broken copper strap on my engine to the fender well allowed the computer eeprom to become corrupted from static developing across the PCM. These ground straps are extremely important. The Chrysler also had a grounding eyelet corroded under neath the air filter casing and that ground caused my cooling fans to continually run after shutting the vehicle off and hence; running my new battery down.


   
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