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Jerry, Master Mechanic
Category: Jaguar
Satisfied Customers: 17220
Experience:  ASE Master tech, 30 years experience
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Jaguar S-Type: I have a 2004 s-type with a 4.2 non supercharged

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I have a 2004 s-type with a 4.2 non supercharged motor that keeps overheating. Replaced the radiator, thermostat assembly, and the coolant reservoir. It seems worse when the a/c is running. I just tried the old thermostat but the problem persists. My fan seems to function correctly. What should my next step be? Thank You for any assistance that you can provide! James.

Hello and welcome, Super mechanic here. Thank you for trusting us with your concern. I will do my best to help you with your question.


Unfortunately, it sounds like you may have a blown head gasket and you’ll likely need to take it in to get it repaired or at least do the test yourself.


About your vehicle.


The first thing that you want to do is check the cooling system for any exhaust gases. There is a tester for that, that you can gt from Autozone for about $20. It comes with instructions, but there is a blue fluid that is used in it, if the fluid turns yellow, that is exhaust gases.


Block tester available as:

Napa BK.(NNN) NNN-NNNN/span>


Part Number:

If there are any exhaust gases in the cooling system, that will cause more pressure than desired and will allow the engine to burn coolant and/or heat the coolant up too high. Most times not filling the crankcase with coolant either.

If there are, then there would be an internal engine problem, like a head gasket or head.

Of course, you will want to make sure that the system is full, the coolant is circulating, and the cooling fan(s) are working as well as the pressure cap holding pressure. Thanks

Customer: replied 4 years ago.

Am I better off getting a used motor or repairing this one? I have 98k on this and can buy a used one with around 35k for $1800

It would be best to replace it for that price. If a head is cracked it will be close to that plus all the labor involved. I would rather get the 35K engine for $1800 and not have to worry. Thanks
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