This is an issue that I have not seen visited. Started the wifes XK8 today. Temp guage went right to high after a few minutes,(way above center gauage) when the heater was turned on. When the heater was turned off and A/C was turned on, the temperature went back to mid/normal. Could hear it was hot when heater was on as both fans came on and exhaust was crackling badly when shut off. As long as A/c is on, it stays normal temp. Any suggestions? I ususally experience the oposite affect ...

 

( moved thread from General Tech section to XK8/XKR section )

Any abnormal rise on the Temperature Gauge needs to be investigated immediately. The V8 can be seriously damaged in a very short time by overheating.

It could be a faulty Temp Sensor but the 'crackling exhaust' suggests otherwise.

Graham

 

Air in the heater core perhaps?

Have you recently had any hoses replaced, a cooling system flush or other service that could introduce air?

Any indications of low coolant after this happened?

 

As has been pointed out previously, remember there is less than a five degree spread between a normal, center scale indication on the the factory coolant gauge and a red zone overheating condition. That is why I sell RealGauge.

My guess is that you have a stuck thermostat. It may be that the fan speed is increased when the air conditioner is running.

As GGG mentioned...do not mess around with repeated overheating or you might be very sorry.

 

Dont know how it happened but when I opened the coolant lid on the top of the engine, it was dry. Filled it up and whola no more overheat. Just curious why the holding tank showed full. Will check for a clog in the overflow hoses tonight.

 

The magnetic float inside your tank may be stuck.

Sorry to keep sounding alarms, but this is a really bad combination with a possible coolant leak, a bad coolant level sensor and an overheating situation.

If the coolant level gets low enough, the coolant can get below the temperature sensor and you may not even get an overheat indication. If your coolant level sensor is not working you will then not get a low coolant warning. This is a fatal combination for your engine as you can overheat and never know what happened.

 

Thanks for the info. The 'donut' ring was floating loose in the reservoir tank so I Ordered a new coolant level sensor and t-stat. Now shes telling me the cabin heater isnt working. When it rains it pours...

 

Actually the donut ring is part of the tank. The sensor is completely external.

 

Be sure to fill the engine through that little black plastic cap near the thermostat. Don't overtighten it! If you fill a low or empty system through the reservoir only, you can get a lack of heat, and inconsistent temp gauge readings, etc. BTW, if it was low on coolant, there IS a reason. Start looking for coolant under the car to give you an idea of where to start looking. The water pumps are suspect (leak in front), the joint at the rear of the right cyl head is another, and the joint behind the throttle body is typical. Places to start.

 

It happened BECAUSE YOU HAVE A LEAK.

Even more urgent than resolving the 'Low Coolant' warning and the Temperature Gauge inaccuracy is finding and fixing the source of the coolant loss immediately.

The warnings of doom in this thread are very real. Plenty of actual reports on the forum about Jaguar V8 engines being seriously damaged or destroyed very quickly through coolant loss or restricted coolant circulation.

Graham

 

I would just add that if you have an original black thermostat housing, to check that as well for slow leaks. Mine developed a hairline crack in it that took a long time to find as the coolant was basically evaporating when it leaked out. There are plenty of really helpful links on here on how to replace it (with an aluminum one), and I'll testify that it was pretty easy to do given the guidance provided here by other Forum members.

Good luck!

 

Does anyone have experience with heater core hose leaks.. My 99 overheated due to broken pully which broke the belt which caused overheating and blew open the resevoir. After fixing those problems, a return hose broke and was replaced. I am still experiencing coolant loss and think it a hose to the heater core.... any help appreciated.....