Looking for help on a 2003 Jaguar S type v-8 not supercharged. Ok so Ive been working at this for a couple weekends now trying to help a family member out and can’t seem to make any headway. What’s happening is coolant is boiling back up and out the expansion tank and coming out the lid. The car is not over heating ( at least that’s what the gauge says) and the hose coming back out of the radiator to the thermost at is warm. The radiator is new only probably 6 months old and it was not boiling out after that was put in, this just started out of know where. While the car was running and boiling I felt across the radiator and it was boiling hot at the inlet and about half way across gets really cold. I did pull the radiator out and ran water through it and it went through it with no problems. The expansion tank has been replaced and I also have tried the new cap it came with and the old cap from the old expansion tank. The thermostat and housing was replaced not long ago, I even took the thermostat out completely to make sure it was not the cause of the problem still no luck. The water pump had a small leak at a bolt so I replaced the water pump with a new one as well still same problem. So I went ahead and did a pressure test on the system and it held something around 14psi for at least 5 min and couldn’t see any leaks anywhere. I then did a block test to test for combustion in radiator it also came back ok. The fan seems to be kicking on when it should I’m running out of ideas on what it could be, Heater is on when I burp the air out of system and gets hot so I don’t think anything there is the issue.
Sorry for the long post I think I put everything in here that I did, please any help would be awesome thank you...

 

Sadly the dash gauge is almost useless (until the head warps) so be careful not to let the engine get too hot. Er... what is now happening is scary.

Any chance there are parts of a broken water pump inside?

Or any other blockage?

Thermostat in backwards? (It does happen.)

 

 

That stuff is not good. Even as a temporary fix its better recovering the vehicle and not running it. My V6 DCCV valve was clogged up with it and it gets everywhere in the cooling system. Its like some kind of grey vermiculite and it expands with heat.

It is possible to buy a brand new and duff thermostat.

 

 

If stop leak... may well have written off the engine. Try to get it all out.

 

 

The S-type thermostat operates differently than the typical style. If removed, virtually all coolant will bypass the radiator, meaning no cooling will occur. A long-winded explanation in post #41 in this thread:

https://www.jaguarforums.com/forum/s...3/#post1693028

Can't guarantee a new thermostat is your fix, but this isn't like older vehicles that would run cooler without one. You need a thermostat installed. Before installing one, test it for accuracy. Here's my tale of work when the existing one failed, followed by a replacement that wasn't much better:

https://www.jaguarforums.com/forum/s...rature-186873/

Here's another recent thread of a replacement bad from stock:

https://www.jaguarforums.com/forum/s...estion-198446/

Both threads above have a link to details of the deliberately misleading dash gauge. Make sure to read up on that, too.

 

 

 

What happens if you leave the radiator cap loose so it does NOT build pressure?

Has the cap been replaced?
.
.
.

 

 

Did you follow the correct procedure for bleeding the system as that appears to be the problem. Refer to the Workshop Manual for the correct method.

I personally have never had luck with using anything but an OE thermostat. The ones from the parts houses seem to cause the engine to run hotter than it should.

Use an application such as Torque Pro through the OBD port to determine the system coolant temperature. The gauge on the instrument cluster does not change its indication between 85C and 129C, which is a serious problem.

 

Please oh please tell us you tested the old thermostat before reinstalling it. As previously discussed, I went through a LOT of grief when my thermostat failed and the replacement was bad, too. I finally purchased a second replacement (from a different source) and compared all three side by side in a pot of water on the stove. Only then was I able to verify what was actually happening.

Also note I had a hard time getting my infrared thermometer to give a precise value for the coolant. I think the fan blows too much heat from the radiator onto the front of the engine. Under different scenarios, my scanner was showing a wide range of internal temperatures, but my infrared thermometer kept showing a fairly constant value on the external hoses. I think heat blown back from the radiator was the culprit.

 

Have you tried testing for hydrocarbons or carbon dioxide in the expansion tank?
bubbles in the coolant can also indicate that the head gaskets are damaged

https://repairpal.com/how-to-test-for-head-gasket-failure