I am an officer with a police department. I have a 1999 Ford Crown Victoria with the Police Interceptor. I have been having a problem with it overheating. The mechanics at the maintanence center told me that they have changed everything on the cooling system. My question is if everything has been changed and checked why does it appear that my patrol car keeps over heating? Also, when it appears that it is overheating the temp. guage shoots up and then comes back down into the normal range, but the dash light stays on. When it does this there is plenty of fluid in the resivoir and nothing over flows. PLEASE HELP!!!
Question, is it actually overheating or does it just appear to do so? If it only appears to do it, then you might possibly have a bad temp. sending unit.
Other than the temp guage and warning light, do you know that the car is overheating ?
An infra heat check of the engine and a water temperature check should establish if the car is actually overheating or if this is just the guage or sensor.
From your description, I’d tend to suspect a failing temp sensor.
I’ll see if I can throw some suggestions out there.
Do you know if they pressure tested the system? Even pressured it up and allowed it to sit for 10 minutes or so to verify any pressure loss no matter how small?
Here is one oddity that I really don’t understand completely myself. A friend in another state has an '01 Lincoln LS that was overheating (even a few minutes after startup) with temp gauge spikes in the first 5 minutes, etc.
The problem was a crack in the plastic coolant resevoir. Now one would think if the coolant was full the car would not overheat or act this stupid, but it appears that slight pressure loss can cause this.
She suffered this for about 5 months until the bottle was replaced and not a peep since. It also appears that’s it’s a fairly common problem. Lincoln it’s true, but…
Another possibility could be the radiator cooling fan. Some Fords of this era (T-Birds, early Lincoln LS, etc. used a hydraulic fan instead of an electric one. The fan ran off of fluid pressure and was problematic.
It’s also why the '03? I think and later Lincolns went back to electric fans, which also have a low and high speed.
Another possibility, and this falls into the slight pressure loss category like the coolant bottle.
I assume your cruiser has the 4.6 engine. The police units were usually equipped with an external oil cooler. The oil filter is mounted on a block mounted flange and coolant runs through this flange.
The flange gasket is a 1/8" thick plastic block with rubber inserts. Over time the rubber crushes down and coolant (and pressure) can be lost either past the flange OR worse, coolant can mix with the engine oil.
This flange gasket problem is not that rare.
Just some oddities anyway and hope some of it helps you out. 
Have the mechanics check the coolant for combustion gases. This sounds like a head gasket leak. When you get spikes in the temp and then it goes back down right away, it can be because of an air bubble being formed from combustion gases getting into the cooling system and blocking the flow temporarily. Another way would be to take the radiator cap off and see if small bubbles can be seen in the coolant.
Make your chief aware of the problem. A 1999
I am betting on the temp sensor. Get those guys in the garage to check the actual coolant temp.
FYI, this car has a two-speed electric-only fan. Earlier models had both a clutch fan and a secondary electric fan.
This car also has fail-safe cooling. If it gets way, way hot, it will switch off half the injectors at a time and run at low power. If it gets really too wa way hot, it will shut off.
The next time the gauge goes up to “hot” pull over, open the hood and see if there is any sign of boiling over. If all looks well, it’s probably a bad sensor sending a false signal.
You might check this site, as there are many P-71 enthusiasts (including myself) who know these cars inside out…
Forgot…Click on “forum list”, go to 4.6 tech talk.