2003 mercury grand marquis overheating, after replacing fan and thermostat


Asked by Jun 11, 2015 at 01:20 PM about the 2003 Mercury Grand Marquis LSE

Question type: Maintenance & Repair

My 2003 mercury grand marquis is overheating, even after replacing the fan and
thermostat.  There does not appear to be any problem with the water pump.  I can drive it
all day at hiway speeds, but in stop-and-go traffic, it starts to heat up.  Any ideas?

12 Answers


Sounds like radiator sometimes the water pump looks good but may not be tho u need to get a radiator. Tester to see really it will test all


Auto zone test that

1 of 1 people found this helpful.

Are you sure the fan is coming on? maybe the thermostat switch is bad. Bad radiators usually show up at hiways speeds,

1 of 1 people found this helpful.

The fan is coming on. It never gets too hot on the hiway, regardless of speed. It only gets hot in stop-and-go traffic, and then not all the time.

6 of 6 people found this helpful.

Still symptoms of fan not coming on. Did you replace the thermal switch that turns the fan on?. The other thing I would do is pull the radiator and have it checked/flushed. Doesn't cost much, and a good thing to do anyway. How many miles on car? Replace upper and lower radiator hoses at the same time. I've had too many breakdowns due to cooling systems, that I always lean towards overkill. When things are right, these cars run "cool as a cucumber".

1 of 1 people found this helpful.

This reminded me, once my Grand Marquis was overheating while on vacation with my Wife & dog. I pulled the radiator when I got home and took it in, and it turned out it wasn't plugged inside, but the outside was clogged with dirt so air couldn't get through. One can't tell, because the A/C condenser is in front of the rad. Have that puppy pulled, cleaned, flushed, new hoses and coolant. One is supposed to do this anyway, just as routine maintenance. We all tend to neglect our cooling systems until something goes wrong, and it's always at the worst possible time. I could tell you stores. Too soon oldt, und too late schmart.

1 of 1 people found this helpful.

Still having the same problem. I noticed that when I had the thermostat replaced, they used green universal coolant. I'm going to find a shop to pull/clean the radiator and use yellow coolant as specified by Ford. In fact, I may just go on and buy Motorcraft coolant. I've already called two shops that don't use anything other than green, even though one guy admitted it would be best to use yellow.

1 of 1 people found this helpful.

I've been using green and my 2002 is cool as a cucumber. How about the thermostat that turns on the fan? My first suspect.(or the relay)


Did you pull the radiator and have it flushed and checked? That's what I said to do if the fan's coming on in traffic.


I'm going to have it cleaned/flushed, and I still may go on and replace the coolant with yellow, even if I have to go to Ford to get it, just for my own peace of mind. The fan and thermostat were replaced together about a year ago. But I have not checked on one thing: Isn't the fan supposed to come on with the a/c regardless of the temperature?

1 of 1 people found this helpful.

I think you're right, it comes on with the AC, I'll check on mine tonight. See if it's coming on. The radiator guys will tell you if there was a problem with the radiator.


Finally found the right mechanic... Did I mention I have an interceptor package? Previous mechanics did not look up parts by the VIN, so I had the wrong thermostat, plugs, and INTAKE MANIFOLD! The 'regular' one is smaller that the interceptor, though it will fit. Also found some jelled coolant in the manifold. It wasn't cheap, but had it all replaced, and it runs like new.

1 of 1 people found this helpful.

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