1998 Grand Marquis LS Overheat

Check the fusible wiring link near the battery and fuse box. Sounds like it has burnt.

there are several problem that will give this indication and your information is not comprehensive enough to make a good diagnosis
the time factor is critical as some time could be 5 minutes to 5 hours and driving is too loose as it could be at highway speeds or stop go traffic , hill work or under load
so I will give to certain conditions that will over heat the car or cause a rise in operating temperature
head gasket--check with compression test
low water level-- check at cap
faulty radiator cap--have tested
partially blocked radiator--have a flow test done
fins on cores falling off --replace radiator
overheating transmission oil--check the transmission is fully operational as high speed with out over drive in will cause a rise in temp
if in traffic --check viscous fan and fan operation if electric
if under load -check load and tyre pressures
check for brake operation- adjust hand brake to full off
run the fault codes to check air/fuel ratios and timing
check for failed cat converter-- blocked exhaust system

Hi Carnell,here's a link to your cts. Where is the coolant temp sensor located on 1998 mercury grand marquis LS...

The drive cycle is a 15 mile jaunt that reaches full operating temperature for the engine and exceeds 50 mph for about 5 minutes
i was told

Have a shop test this for overheating, I think you have a big problem here. The light is indicating the overheat. Do not drive this or you can ruin the engine.

Hello, By doing RR most of this doesn't work. What you really is a auto technician to run some test on you car. The one test they really need to do is a pressure test on the coolant system on this Mercury GM. This pressure test will indicate if there is a leak down. That is, coolant is leaking. With coolant leaking a a closed pressurized system isn't best thing for these modern vehicles.


The coolant system is a closed system and the manufactures designed the system to hold pressure above 240 degrees. By raising the boiling point by pressurize coolant system.
This helps pollution system to operate more efficiently. GB...stewbison

This could be a broken head gasket, cracked head or block.

Pull the thermostat back out and you should be able to see water flow through the radiator. Make sure the water pump is working.

Were does the antifreeze leak from?

Hi, the orifice tube always goes in the high side , the thinner line, most of the times close to the evaporator...an easy way to find it is touch with your fingers the line ,in some place will be hot and in another cool , when it change from hot to cool there is the place, most of the time is close to the line connection....

do you have aftermarket headlights with too high a current draw?

What does the owner manual say fuse 9 portects?

Sounds like the thermostat is stuck closed.
If the car is overheating, they will also hurt perfomance.

But after sitting 8 yrs, it's hard to say what else might be wrong.
Was it just sitting, and you threw some gas in it to get it running? Or did you go through the car first to do some maintenance? Like an oil change, flush the gast tank and carb and put in all fresh. Change the fuel filter? and the list goes on. A car sitting that long can develope some problems just from sitting. If you could list what you have and haven't done to the car before this would help.