That is crazy how those O-rings just melted. All that work... I upgraded mine with aluminium ones a while ago and so far they've performed well, no leaks for now and it's been 6 months and 5K miles, so I hope they will hold up for good.

 

I took clubairth1's recommendation and put JLR OEM seals (part # AJ811600) in the MITZONE aluminum rear manifold rather than keep the o rings it came with. I also replaced the sensor with my original OEM one. So far, all is good. Also worth noting: I had ordered the Euro Amp rear manifold as well just to compare and the two castings were identical complete with the same flash and casting marks. I suspect they came from the same factory. Neither one came with those red o rings that melt but I didn't trust them regardless.

 

Same as Freddy. Alloy + OEM seals.

wombat

 

The drain plug is at the bottom of the radiator on the passenger side. Plan on it being stuck. Then you will damage or destroy the plastic head on the drain plug. The rubber washer swells a bit and now it will unscrew a thread or two and lock up. BUT don't despair! Just a bit of WD40 sprayed on the drain plug and a bit of back and forth on the drain plug it will spin right out. Just need to get that rubber gasket lubed up a bit.

A bit hard to see but if you go back up thread to my drain plug picture you can see how it's made. A plastic body with a rubber washer against the head of the drain plug. The washer is our problem.

Boy if you had not said something I would have bet that red stuff was just too much RTV! Now sorry to go off thread but since the JLR seals were mentioned for the rear water manifold I will post that again.



It's looks a bit odd as it's not a plain O-ring.
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I have never seen anything other than RTV look like that, and have never seen any JLR coolant pipe that had red "gaskets" of any kind.
The nice thing about the stock AJ811600 and LR010793 seals is that they are $12 each and there is not the typical difference in pricing between Jaguar and Land Rover. Bonus, the LR010793 is available from FCP Euro.

 

Me too Josh but he said it was not? And they were aftermarket seals not JLR supplied.
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No RTV, here is a picture of it prior to install

 

I also had an issue with another aftermarket aluminum pipe the mounting screw holes didn’t line up at all. I had to saw the tabs off just to connect it to the other pipe. Right now it’s only being held in place by zip ties and the other coolant hoses connected to it. When I replace the thermostat, I’m planning to switch to an OEM one, assuming the OEM pipe properly fits onto the aftermarket metal pipe near the oil cooler.

 

Your coolant pipe is being held in place with zip ties?? Are you sure you purchased the correct pipe for your application?

 

I replaced the thermostat so many hoses and clamps like doing heart surgery and took the leaking one apart afterward it looks brand new inside and out with no signs of damage. I honestly can’t tell why it was leaking. I think one of the screws may have been loose and just needed to be tightened.

If anyone else has a new thermostat leak Might be worth checking the screws before replacing it.

 

Thanks for the pics. It would be awesome to have only the screws to tighten, but I have a feeling that the rubber gasket may be the culprit, if the housing isn't cracked. I am about to take on the project of replacing the thermostat in mine, but it only leaks very slowly, so I am dragging my feet in getting it done. I will try the screws first, just in case that's all it is.

 

Thanks for those pics. Looking at the guts removed from the housing, I wondered if its feasible to transfer the JLR OEM thermostat mechanical parts to an aftermarket aluminum housing. If the internal dimensions are identical you could do it but I have doubts. My doubt is because of the experience with the rear manifold. I know for a fact that the internal dimensions of the aftermarket aluminum rear manifold long legs are not the same as the OEM plastic part yet they did make bore for the sensor the same as the OEM. - Just contemplating if the idea to get away from the plastic could be done and still keep the trustworthy OEM thermostat guts. Probably a risky experiment. Lotusespritse had the same thought.(#6 this thread).

 

Here is what the Aluminum ones look like taken apart. This one had a 95C thermostat in it.





Tried to keep the parts in the order they came apart.





Another view.





Thermostat fully assembled.




It's got an O-ring seal. I wonder if your plastic one had a crack somewhere that is hard to see?
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Well, it looks like I owe "JaguarXJL15" member a beer. He suggested to tighten the screws holding the thermostat housing as he couldn't find a crack. I was ready to replace my thermostat with an aftermarket aluminium one, but tried the screws on the OEM first and while they weren't loose, they each took at least a quarter turn. I tested the system with the pressure kit/pump and it held for an hour at 25psi with zero leaks. So, I decided to keep the OEM in place and return the aftermarket one. Problem solved. Thanks again "JaguarXJL15!"

 

Glad to hear it worked out 👍
Sometimes it really is the simple stuff. Those thermostat housing screws can loosen just enough over time to cause a leak without being obviously loose. Good call pressure-testing it afterward that’s the best confirmation you can get.

Nice save on keeping the OEM thermostat too, Thanks for posting the follow-up; it’ll definitely help the next person chasing the same issue.


When I first removed and opened my OEM thermostat, it honestly looked toast. But after the new aftermarket thermostat started leaking, I opened that one up to inspect it as well and everything inside looked brand new. That’s when it became clear the issue wasn’t the thermostat itself, maybe a loose screw.

When I checked the screws,( before opening them) one of the screws on the new aftermarket unit also turned about a quarter turn. So it really does seem like a loose screw was the cause all along. Makes me wonder how many of these thermostats get replaced unnecessarily because of slightly loose housing screw

 

Agreed JaguarXJL15! I am sure many thermostats have been replaced without the need to replace them. The housing is really solid and thick, unlike some other parts of the cooling system. Jaguar should have issued a bulletin to check the screws first, but I doubt they ever figured this out. Anyway, the original thermostat works well, so I preferred to keep it if at all possible. I will keep an eye on it just in case it starts leaking again, but hopefully I won't have to worry about it again. Thanks again and happy motoring!

 

Interesting find. I may apply blue Loctite on the bolts on my aluminum thermostat as a result. This common practice in the diesel and commercial world but you don't hear about it as much in the automotive aftermarket. Good work!