I drove the car for 15 miles stop and go driving- no problem, temperature normal.
I drove the car for 15 miles on the highway - no problems, temperature normal.
Sitting at the light on the off ramp the temperature gauge started ticking up, went up to 3/4 and then leveled back off. Coolant light came on and went off.
I drove home 3 miles with no problems. No coolant spilling, fan wasn’t running.
Coolant droplets and residue were on the top of the overflow compartment. After it cooled I opened the cap and added ½ gallon of antifreeze to bring it back to MAX.
I started the engine, unscrewed the bleed screw and let the car run for 3 minutes as it bubbled and began overflowing through the screw.
It’s getting dark here so I’m done for the night. Tomorrow is another day, I’m open to suggestions/insights/encouragement!

The oil is fine.

 

How do I check the air flow side of the radiator to make sure its clear and the pump?

 

When I read this I thought of blown head gasket.. as experienced Subarist. Hope I mistaken.

 

Having had coolant blown out on a Rover V8 in the 80s, (this was a Buick design BTW), and then again with a Jaguar XJ6 Series 3, with consequent overheating, and both were caused by head gasket failure, there has to be the possibility of it here.

Combustion chamber gas pressurises the coolant and the coolant then gets blown out of the header tank past the pressure cap. One feature of HGF like this can be pressure in the coolant jacket even when the car is completely cold.

There is an awful lot of coolant disappearing here, and there should be some evidence of where it's going, I'm sure.

 

If indeed is a blown gasket the tell-tale sign would be white "smoke" coming out of the exhaust pipe. If indeed this is it, it will get much worse very quickly.

 

I experienced coolant pressurised from expansion tank as exhaust gases displace coolant from upper tank, which is highest point of the system, down to expansion tank which is just open bottle, until its overfilled and then blows coolant into engine compartment. But this is a particular problem with turbo engine with big pressures around 23-25psi and above. Problem begins slowly on high engine load and intake pressures and becomes worse over time at lower pressures and engine loads until you tired to refill upper tank from expansion manually..


I have no idea when coolant goes into combustion chamber causing "smoke" and particularly in n/a engines.. maybe its just matter of high mileage and real age of gaskets or total damage of gasket in turbo example described above.


I heard of problematic 4.2 NA motor in comparison to SC version, but without any proof yet.

 

I wonder if there is something wrong with the electric cooling fan as it sounds like it may be working intermittently.

 

Some questions.

When you say you replaced the thermostat housing, was this the complete thermostat unit housing?

Can you get the coolant system pressure tested?
This may not show anything, as I suspect the leak is very small.

Does/ has your low level expansion tank alarm worked?

Can you check the coolant for combustion gases?
At least this will put your mind at easy that it is not the cylinder head gasket leaking.

You may I suspect, have a small leak,(very small) on the coolant pipe between the back of the water pump and the throttle body (this would be the prime suspect.)
As it would not be visible in most part as the majority of it is under the air manifold. Similar to the valley pipe position on the S type R's. and a lot of the coolant would evaporate off.

Mine started to have low coolant level/alarm and I could not figure it out, nor find the leak. But eventually did when the thermostat housing went.

Throttle Body coolant line AJ 811763, was the pipe. Mostly hidden under the air manifold. There is a larger dia pipe about 4/3" into the back of the water pump, and a 3/8" into the throttle body. The connection reducer (plastic fiber type) between the two pipe sections had cracked, and was leaking coolant out between the cylinder heads, and down the back of the engine. None was to be seen on the ground, only a small puddle on the under tray, and soaking the foam.

What makes me suspect this, option of leak and low coolant, is the turning on of the climate control, and the overheating, as the water is further reduced from the cooling system and is pumped into the cabin heater. Together with the then normal running temp and then the overheating over time as the coolant is lost.

It took weeks for mine to register low level in the expansion tank.

Then again this explanation only really works if the expansion tank level alarm is not working, and this could be rubbish and not this pipe or coolant leak at all.

But a good story and a better ending than cylinder head gasket replacement.

below photo of the hose I am talking about. #7

https://www.jaguarforums.com/forum/a...ody-hose-2.png