Why is my car overheating?


I have a 1999 Crown Vic. (90K Mi), I’ve owned her for two years, that overheated after a monumental snow storm this past February. The day before car was running for about two hours in my parking spot while I shoveled out of the mess. Traffic was very slow the next day and I put a heavy load on engine going up hill after about half an hour ride when overheating occurred, analog display shot up from normal operating temperatures of 1/3 to 1/2 way up to overheat and symbol lit up (not flashing) . I found a safe place and pulled over.

Coolant level was fine, no leaking antifreeze, system seem pressurized, upper & lower radiator hoses felt hot so I believe coolant is circulating OK, and fan was blowing when car was overheating. I figured day after huge storm AAA would take too long to tow me so I sit with car for an hour or so then drive home, running a little rough so thinking fail safe may have kicked on alternating cylinder operation although the check engine light didn’t light up nor did overheat symbol flash.

Inspected car, nothing seems wrong & can’t get car to overheat again. I’m thinking ice or snow was blocking radiator or thermostat shot or frozen or something. Drive car normally, about 20 miles each way to/from work, city then highway, with traffic for about half an hour forty minutes each day without recurrence until a couple weeks ago.

After 20 minutes on ride home on highway I hit traffic, car overheats, display shoots up from normal operating temperatures of 1/3 to 1/2 way up to overheat and symbol lights up (not flashing), I immediately cranked the heat, temperature gauge drops a little so symbol not lit up I pull over, open hood see fan motor running high speed, no apparent leaks so I shut off car, wait an hour and limp home again.

I replaced the thermostat, let car warm up to 1/2 way on gauge but radiator fan not engaging, coolant flows when car given gas. Turn on A/C to max cooling and fan kicks on for about 6 seconds and turns off and doesn’t come on again. Coolant looked dirty so I bring to a service station the next day who flushed the radiator. I told them about fan not turning on I believe they pressure tested system and he told me they jumped fan motor which went on but blew a fuse which he replaced, no cost.

I replace the cooling fan relay & 30 amp cooling fan relay fuse. The fuse they put in had a solid aluminum casing which I couldn’t tell if it was blown and fuse was 3 - 4 bucks. I run car till temperature gauge gets to 1/2 way mark but radiator fan not engaging. I’m now thinking fan motor may be bad. This P71 came from an auction in Florida three years ago, I’ve owned her for the last two years and from maintenance records I see car was driven for several years, then last five years in service had about 1000 miles a year on it until sold at auction so fan motor may have had lots of use idling in Florida heat.

Drive car to work every day till next paycheck but car overheats on highway, after hitting slow moving traffic jam so I call AAA and get towed home last nine miles or so. I am convinced I figured this out so next day I replace fan motor, check pigtails which were not oxidized and wires didn’t look burned, run engine till 1/2 way up gauge but fan motor not kicking on, turn A/C to max & nothing. Check 30 amp fuse which is blown so I replace it. Rinse, repeat and same result motor not engaging now but fuse did not blow. Which brings me to today.

I don’t have a volt meter to check relay and could probably figure out how to jump fan motor to check but I’m at the point where I may just figure out how to connect toggle switch to radiator fan and manually switch on when needed.

I think the only thing I haven’t replaced is the coolant sensor by the thermostat but I don’t think that’s the problem. I am hoping I haven’t replaced a part with a defective part or somehow caused more of a problem. I have researched on line forums, manuals and videos before each replacement and believe I did a good job replacing parts and that all replacement parts are good. I have worked on my past cars so I’m not too green.

Should I bring this to a dealer or mechanic to run electrical or computer diagnostic tests? Is that something they do? I don’t have unlimited funds to have a dealership start replacing coolant system piece by piece and thought I could do this without too much trouble but I am stumped.

I am hoping this is something someone has heard of before and can help with. Sorry for the long history.

Ugh… These Crown Vics are Phenominal Performers…The last one I worked on was SOLD running happily with 330K on the clock.

You need to slow down here…as you are mixing in lots of info that I understand seems important…but is only muddying the waters

You have smoothed over so many details here I dont know where to begin so I am going to answer this by saying…I have read your post and I am just going to answer with all I know about this car and what you have said

When you idled this vehicle for SOOOO LOOONG in a snow storm/cold weather…you were at great risk. WHat PROBABLY happened is that you over heated her then and there… and you also had a significant coolant loss in the snow…which then caused an AIR POCKET IN YOUR SYSTEM

I also need you to just step back and try not to think of all your confusing details in trying to diagnose this and just go with what you know…by methodically finding answers to simple questions.

While these Vics are unbelievably rugged…they have a flew flaws that have actually been addressed…the intake manifolds are made of plastic…and they crack and leak coolant…they make a newer updated model… Your manifold is probably spent…look for evidence of this instead of taking my word…just know that they are KNOWN to fail after a long service life. When they fail you can see coolant in certain areas…and the coolant can ground out the coil over plug system…look inside your coil /spark plug holes for liquid/coolant…if it is wet down there…the manifold is leaking coolant into the holes…this will disable/shutdown that cylinder

You need a voltmeter at the very least to work on this issue…for many reasons…checking the fan relay…checking the coolant temp sensor etc

The fans should come on by DEFAULT when your A/C system is charged and working properly…there is your fan motor test…to see if they are capable of running…after you do that raw test (and there are other raw tests for the fans)…you then need to look into the sensors that trigger the fan relay…and the relay itself

Here is my advice…look at your intake manifold and study it for leaks…CHANGE your thermostat…>REFILL your radiator…AND BURP THE AIR OUT OF THE SYSTEM…Test your Fans…then the fan relay…then the temp sensor…

Youre missing something simple here and need the tools that you need…so get them if you want to fix this yourself.

We need the results of each item I mentioned that you should check…and their results… This is a step by step process…

Id be happy to help further…but you have some work to do here…let us know…


Thank you for your reply Blackbird,

Steps I have taken,

Replaced thermostat, brought car to mechanic who flushed radiator,

Then replaced cooling fan relay & cooling fan fuse,

Then replaced cooling fan motor.

I have not seen any leaks, no antifreeze in oil or around spark plugs.

I was aware of plastic manifold recall and tendency to crack but figured if it was serviced regularly that it was replaced before it was auctioned three plus years ago.

I have not replaced coolant sensor by thermostat yet but since mechanic jumped fan motor and blew 30 amp fuse, which he relaced I was thinking it may be something electrical.


We have these same engines in our Ford trucks at work and I can tell you from experience that the cracked manifolds aren’t always super obvious. I recommend removing the 2 front most plugs and looking down the hole. If there’s coolant in there, you have your answer. You may also see that part of the gasket is visible. If that is the case, the manifold has split.

Don’t you have a mechanical fan clutch?

Have you ever heard it engaging?

I’m not sure at what exact temperature it engages on your car, but it should have been screaming, trying to cool down your overheating engine.

Thank you db4690,

As you and Blackbird have suggested I will remove spark plugs and look for fluid. I had only inspected what was visible and didn’t see any leaks while engine was hot.

The only time I got the fan motor to engage was when it was hot I cranked the Max A/C which turned fan motor on for 6 seconds then stopped. I didn’t hear anything trying to engage when the engine got hot. I will try to listen for that,

@MassP71 I’m talking about the mechanical fan, NOT the electrical fan

The electric fan should be in front of the condenser, right behind the grille

The mechanical fan is driven off the water pump, I believe.

I have a 1999 Ford Crown Vic P71. Car had a bad fan and would overheat only when the A/C was on,fan would shut off when A/C was turned on. Replaced the fan and it worked okay for about 3 months. Today it was about 85 degrees outside. Drove the car for about an hour without the A/C on. Car ran fine,fan cycled on and off. Shut the car off for about 30 minutes. When I got back in the car I turned on the A/C and it was blowing hot air. Cooling fan would not come on. Turned off A/C and car still kept getting hot. Checked and the fan wasnt on. I let the car cool down and kept A/C off. Drove the car about 30 minutes and with the A/C off the fan was working again. Got home checked to make sure radiator was full of coolant. Let care get to normal temp and fan came on. Tried the A/C and as soon as the A/C came on the fan shut off and A/C was blowing hot. A/C compressor was cycling on and off rapidly. Before today I have driven the car in 90+ temps with A/C on and had no issues. Checked Refrigerant level and it was full.