Question about 1998 Jaguar XJ8L

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Xj8L 4.0 Engine overheated

Took into a jag shop to have a tune up change thermostat thermostat failed now the hosing was bad replaced that now they say the top hose is holding to much pressure they say maybe exhaust is getting into it Blown Heads ?

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  • DOUGLAS W. PINE Jan 29, 2009

    Thank You John,

    This is very helpful information I have a Dealership that is trying not to take the rap for this ! I took it in for a tuneup had the oil spark plugs and antifreeze change while they did that I had them change the thermostat I had it for two days the first day I had to pull over it felt like I had lost my acceleration no leaks at this time none at home then the next day my top hose blew off put it back on filled up with water took it to the shop and they found out that the thermostat was bad they had a bad batch while testing this the housing was swollen they tried to have me pay for that, they finally payed. Now they are reading carbon monoxide and they are trying to play dumb I'm not a mechanic but know a little about cars

    What do you think, after talking with me they are now seeing if there warranty department will cover this I haven't heard back yet the engine was fine up to this point they say its internal and it builds pressure because of the carbon monoxide and blows the hoses after a few minutes. Thanks again John for you help Doug



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This can easily be confirmed by a carbon monoxide test, on the cooling system, the fluid in the tester will change color proving head / head gasket failure.

If this is confirmed, the spark plugs can be removed and the cooling system topped up, and pressure tested to 15lb 15 min or so.
The engine is then spun over, and any failure should be obvious by the coolant coming out from the spark plug holes.

The necessary repair can then be carried out.

Hope this is of help.

Good Luck !

A FixYa rating would be appreciated thank you.


P.S. This is the 3rd time I have posted you an answer,and nothing is posted up. Gremlins somewhere ?
Third time lucky ?

Posted on Jan 29, 2009


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Did you check the water pump? That is what is sounds like.

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If the car is overheating, especially in cool/cold weather you have a serious problem which needs to be addressed immediately. I very much doubt that the coolant temperature gauge is giving an incorrect reading and if you drive the vehicle with this problem you are risking expensive engine damage. In any event a mechanic can easily use another water temp gauge to check if the gauge in the car is giving a faulty reading.

If the thermostat has been removed - as you say - then there is nothing mechanical isolating/blocking the full flow of coolant between the radiator and engine despite the engine operating temperature.

Removing a thermo because of a previous overheating problem is not a sensible move because it does not address the underlying cooling problem issues. An old or faulty thermo should always be replaced with a new one and the causes of the overheating investigated and fixed. The fact that the thermo has been removed suggests that there was a cooling problem previously and it is likely that it was not due to a sticking thermostat.

Overheating can be caused by and one or more of the following:

1. Low coolant level. Check the coolant and top up. All coolant hoses (including heater hoses) need to be checked for deterioration and leakage. Suspect hoses need to be replaced .

2. A sticking thermostat which impedes the flow of coolant between the radiator and the engine when the engine warms up. A new thermostat needs to be fitted.

3. Debris in the coolant which is impeding coolant flow through the engine. Coolant needs to be changed every 2 years and the system flushed to avoid this problem and to address deterioration of the coolant mix.

4. Air locks in the cooling system from the inadequate bleeding of air from the system.

5. A faulty / corroded water pump. If the water pump has never been changed or you have no record of it being changed in the last few years then it needs to be removed, checked and replaced unless in good condition. A faulty water pump cannot push coolant through the system (or flow it fast enough) and your engine will definitely overheat.

A badly tuned engine can also cause an engine overheating problem in certain circumstances but in your case I suspect the issue is definitely with the cooling system as outlined above.

We cannot test and inspect your car so it is not possible to identify the exact cause of the problem in your case. I hope this helps and please get it checked out straight away by a reputable auto shop. Otherwise you are risking expensive engine damage and having to replace the vehicle entirely.


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