My 1998 jaguar xj8 over heating light comes on when car is idling in hot weather but when driving the temp gauge goes back down to the middle. When temps are 70f and lower the temp gauge goes up a lil from middle while idling after 30sec to min but never red zone.

NO CHECK ENGINE LIGHT ON
NO STEAM
NO COOLANT LIGHT ON

I already replaced Thermostat,Thermostat housing and cover,coolant,seals,upper radatior hose,bypass hose at 100,341
Thermostat replaced again at 101,755

car now has 102,300 miles so i doubt its the thermostat again.


Does this sound like the water pump? If so how can i make sure its bad before replacing it?

 

Radiator fan(s) run OK?

 

yes the fan works and it also runs for a minute after i turn the car off.

 

I'm just wondering....there's no mention of the water pump being checked or replaced?

 

I would stop driving until this is resolved. That temp. gauge is just a glorified idiot light after it reaches mid scale and you could be risking serious damage.

Definitely check or just replace the water pump, and also the plastic crossover pipe and plastic thermostat tower with aluminum if not done already.

Are the secondary chain tensioners original?

 

Are you losing coolant? White smoke out the exhaust (possible head gasket); are all bolts torqued correctly? How old is the lower radiator hose - as they soften they will deflate under pressure. How old is the coolant? All checks out, then time to change the water pump.

It would be useful to run with an OBDII reader that provides real time data attached to check the actual water temp. As noted, the temperature gauge is useless at the upper end.

Last resort change the water pump and have a radiator shop run an IR scan over the radiator.