XJ XJ6 / XJR6 ( X300 ) 1995-1997

Coolant Pressure Question

Old 05-28-2019, 09:00 PM
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Default Coolant Pressure Question

Hello Everyone,

Still trying to keep Duchess going for a little longer and hoping for some advice. I couldn't find any references to this problem on the forum, so I thought I would throw it out there to see what happens.
I lost a belt while motoring down the highway, leading to overheating and a spectacular geyser of coolant through a tiny hole in the reservoir just past where one of the inlet hoses enters the reservoir. Had the car towed to the mechanic and just heard today that they believe that the reservoir needs replacing and should not be patched. I was wondering if anyone knows the type of pressure we are talking about. Is it possible to patch small home (about 1 mm in diameter)?

Thanks for any insights. (The car has other issues and the mechanic has suggested walking away at this point.)

Old 05-28-2019, 09:25 PM
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IF, and that is a huge IF, the tank is still "pliable" and not gone HARD and BRITTLE, a small self tapper with a dob of JB Weld will do the trick.

If its hard and brittle it is likely to crack more.

The pressure cap is 140kpa, from memory??? HAHA, but I found a 100kpa for mine and 8 years on, all sweet. Lower pressure just takes the "strain" of some very tired components, heater core, etc etc.

Same lower pressure applied to all the V12's and the S Type V6 and even the X Type (God bless its little socks), just works for me.

Good luck.

Last edited by Don B; 05-28-2019 at 10:09 PM.
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Old 05-28-2019, 10:23 PM
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Hi Andrew,

I don't know if you prefer kPa or psi in Canada, but in the U.S. common pressure-relief ratings for radiator and reservoir caps is 14 to 15 psi, which is consistent with Grant's 100 kPa, so that represents the maximum pressures most cooling systems are designed for.

Grant's idea of a self-tapping screw and JB Weld will be the easiest repair if it will hold the pressure.

Another idea is that if you can get access to a plastic welder, you may be able to permanently repair the reservoir (at least until another hole opens up somewhere). Harbor Freight Tools carries an inexpensive plastic welding iron that works like a soldering iron but at temperatures suitable for most thermoplastics. I've used mine on lots of plastic repairs. The iron comes with some black plastic repair rods, but if you don't want to use them on your reservoir, you could try strips cut from a plastic milk or water jug. The trick is to heat the plastic of the piece being repaired and the new plastic rod simultaneously until they are just soft enough to "stir" together so they will bond well when they cool. There are videos on YouTube that illustrate the process.


Another idea is that If you have access to the hole in the reservoir from both the inside and outside, you can put a metal washer and rubber washer on a small bolt, push the bolt through the hole in the reservoir from the inside to the outside, install another rubber washer and metal washer followed by a nut, then snug it down. You could supplement the rubber washers with J.B. Weld. But if the hole is too far down on the reservoir this may be impractical unless one of your hobbies is building ships in bottles.



Last edited by Don B; 05-28-2019 at 10:28 PM.
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Old 06-18-2019, 10:16 AM
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Belated thanks to all who answered the call. I might have just thrown in the towel without your advice.
I asked the mechanic to overcome his scruples and seal the leak the best he could - under the understanding that I would not hold him responsible if the seal did not hold - and he did an excellent job. So far so good. We did a nice hot highway run last weekend and no problems whatsoever. Unfortunately, my wife no longer trusts the car and is taking the bus to Victoria this weekend. Que sera sera.
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Old 06-18-2019, 12:46 PM
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If your wife doesn't trust your repair, why not get a replacement tank?


Under $100 so kinda no brainer really.
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Old 06-22-2019, 03:36 AM
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If the engine survived overheating and it only caused a pinhole leak in the coolant tank, then your engine and cooling system are pretty strong! With a new belt, new coolant and thermostat, and new or repaired coolant tank, the car will be solid. I'd never choose a bus ride over a Jaguar drive.
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