Looking for help my 2015 XFR is having an issue where coolant is overflowing from Expansion tank on long drives. I’ve replaced Water pump, Radiator fan, Thermostat, Expansion tank and all the known pipes that cracks. I’ve done the cylinder block test and leak down test and they both passed. No bubbles are in the expansion tank and the cooling system holds pressure when pressure tested. Only issue is the coolant is overflowing when the car is hot. Any help is appreciated

 

Is it overfilled in the first place?
Does it overheat?

 

No coolant level is at the cold mark when the car is cold overnight. Coolant is overflowing on long drives out of the expansion tank cap, no bubbles or anything just overflowing

 

There could be hose collapsing or your new thermostat is bad , it happens, also is the heat consistent

 

Yes, nice one. Take the thermostat out to see if it still does it

 

https://www.jaguarforums.com/forum/x...-234806/page2/

HELP may be the wrong word, but a 59 post thread on the subject.

It is not a coolant leak as such, it is overflowing from the expansion tank. One would think because of an air pocket expanding! All other things being equal.
No previous overheating, no rad seal added to the coolant system, no cracked head or exhaust in the coolant etc.

I would try and burp the system again. If all you have done is change the radiator.

A little story.

I changed out the water pump and front and back coolant header water pipes, and the expansion tank as the float had died. (on the AJ126s)
Refilled the system to the correct level and vented at all points with the car level.

Changed the transmission fluid and filter. which meant going through a few heat cycles.

Over a couple of days, and changed the rear door lock.

Coolant water level fine no leaks.

Raised the back end to tidy up the rear drop links and changed the diff oil.

The expansion tanked emptied! 1.25ltrs gone!! WTF.
Refilled and ran up. No leaks and the car has been good since.

I would may be park on a slope head down, and head up with the expansion tank cap off and run the engine and see what happens.

Its cheap, and what have you got to lose!

 

The only thing that was not replaced yet is the radiator, I do not want to keep throwing parts at the car. I’m wondering if it could be a micro head gasket leak that only happens when the car is really hot. Would the leak down test pass if that was the case ?

 

How are you filling the coolant system? With all the problems that modern cars have with air bubbles and not being easy to bleed. I went to a vacuum filler. These have come down in price and you will be amazed at how well it works.

I just used it on my 2014 XJR and it was one and done. Filled to the top and it stayed there.

If you suspect head gaskets it's simple and quick to check? Even Harbor Freight has a test kit out now a days!
Combustion Gas Tester
It's less than $30 and it will tell you yes or no on the head gaskets.

The leak down test has nothing to do with head gaskets? It is a measure of piston ring and valve stem sealing. Basically an engine wear indicator.
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Did you check the pressure cap on the Expansion Tank? It should be 140 kpa (or 20psi)

 

Check if the fan kicks on at 200 degrees

 

Coolant cap is 200Kpa and yes the fan does kick on

 

pick one of these up and do the bleeding process ,plenty of videos how to do it ,you may have hot air pockets, ill be posting a video how to

 

A strange one for sure. No sign of oil in the coolant? Thinking heat exchanger issue. That's the only source of additional liquid I can think of. Or could it possibly be something to do with supercharger pressure and intercoolers I wonder?
If you have run long journeys it's unlikely to be air in the system, I have swapped lots of these engines (5.0) and they self-bleed pretty well, causing fluid level to drop if anything. Also in my experience the first sign of a failing head gasket is that the heater stops working.

 

Just a suggestion, to rule it out,I had to run mine for 20mins to get the air out

 

Was in traffic at a stand still for a couple minutes and the temp got up to 210F and coolant started to spew from the reservoir cap, I data log and monitor my temps, it should not pass 204F. Started to drive and it started to creep back down to 194F. Now I’m just puzzled. I am planning to do the block test again before I pull the heads off

 

Pulling the heads off is no mean feat. I would not attempt it with the engine in the car.

 

These numbers do not make any sense. If the system is full of coolant and the temperature sensor is covered with coolant and is accurate it is physically impossible for there to be over 20psi in the cooling system and therefore no coolant can be expelled--- the laws of physics will not allow it.
Your cooling system must be vapor locking, uncovering the temperature sensor, and allowing higher coolant temperatures and hence pressure in excess of 20 psi to expel coolant.

 

I would bleed it again
then drive in Dynamic mode

 

Faulty thermostat or thermostat sensor ? But no fault is being thrown

 

Good question and I don't think a failing thermostat sets any codes?
You can read the actual engine temperature in real time? I use the custom PID pack and Torque Pro.

We don't have any temperature numbers and that might help here?
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