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Overheating Problem

09-30-2012, 09:47 PM
Hi, I have a weird overheating problem on my 1998 Grand Marquis. After about 10 minutes of driving the engine overheats and coolant comes out of the reservoir. But after that initial overheating episode the car runs fine and doesnt continue to overheat. It acts as if the thermostat is opening to late. Once the therostat opens everything is fine. If I let the car idle in the driveway and wait for the thermostat to open before I start driving everything is fine. I replaced the water pump and replaced the thermostat twice. Anybody have any ideas what could be causing the overheating? I noticed that there doesnt seem to be much coolant going through the heater hoses. Im not sure if that is normal or how much coolant normally goes through in the first place.

Thanks for any help anyone can give.

10-01-2012, 10:58 AM
Sounds like trapped air. Elevate the front end, pull off the rad cap. Heater on high.

10-01-2012, 02:23 PM
I decided to try to bleed the cooling system. In the Ford technican service manual it tells to bleed the system by turning the heat on full, put the reservoir cap on and run the engine until the thermostat opens and the hot water fills the whole radiator. Then shut the car off, wait for it to cool down and then fill reservoir to proper level. I did that but mistakenly thought it said to keep the reservoir cap off. After about 7 minutes of the engine running coolant started to flow out the top of the reservoir before the thermostat had a chance to open up and I shut the car off. Should the coolant be coming out like that? I then put the cap on to do it the proper way. While the engine was running the fan came on and the thermostat(195 deg.) had not opened up yet. I thought I read somewhere that the fan doesnt come on until the engine temp reaches 195 degrees. The thermostat eventually opened but not until about 5 minutes after the fan went on. Also before the thermostat opened the heater hoses were warm not hot and the heater was blowing just barely warm air. As soon as the thermostat opened the heater started blow hot air, the heater hoses got hot, and the engine fan went off. So should there be more coolant flowing through the heater core than there is when the thermostat is closed? And should coolant be flowing out of the top of the reservoir when the cap is off and before the thermostat is open?

10-02-2012, 11:23 PM
Bled the system and so far so good.

10-02-2012, 11:44 PM
Let us know how it goes.

10-09-2012, 12:50 PM
Sounds like trapped air. Elevate the front end, pull off the rad cap. Heater on high.

With the engine cooled off, open the radiator cap. You may notice the coolant level is low. Fill it up again in the radiator and in the overflow container (to the mark on the container where the engine is cool) and start the engine. This will replace the air trapped in the system. Keep the cap on the overflow container. Put the heater on high. Drive the car around the block till the engine reaches operating temperature. If it begins overheating stop the car in your driveway, let it cool down again and recheck the level in the radiator and the overflow container. Wait for it to cool off before you open the radiator cap. Do this till the engine doesn't overheat.

Make sure you have a good radiator cap, buy a new one if that cap is the original cap that came with the car. They don't last forever. The seal wears down after a while. The system needs to be under pressure to work.

08-05-2023, 08:56 AM
The cooling motor on the radiator may be intermittent...they are required to assist cooling.

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