Coolant expansion tank empty when hot?

A

AL1

New member
Should the coolant measure be the same regardless if the engine is hot or cold?

The other day I noticed a slight occasional hiss coming from my 2016 V6s when cooling after a run out.

I decided to keep an eye on all the fluids to see if there was a leak. When the engine has cooled for a good few hours then the measure is between min and max level in the coolant tank.
But if I look straight after a drive, the coolant tank appears almost empty...stays like this for at least 40 minutes. Is this an issue?
 
When you say look do you mean through the side of the expansion tank or taking the top off? :shock:
Not having done that straight after I drive I can’t give a definitive answer, but if you have done so without scalding yourself then maybe the system is not holding pressure.
There is a bulletin for replacing the coolant header tank due to the neck threads being slightly oval - if you have a digital calliper to hand measure it twice, second time at 90 degrees to the first, and you will get a good idea if that could be the issue.

Edit:
JTB00518NAS1 28th Sept. 2016
If threads <50.7mm replace tank and cap.
If =/>50.7mm and no sealing bead damage replace cap only.
 
Through the side of the expansion tank! :lol: you cannot see any visible line of coolant through the visible window of the coolant tank, after the car has been out for a run.

It was serviced a few weeks back, could an air gap have been created by mistake when replacing the coolant?
I’ve got a 200 mile trip on Saturday so don’t have enough time to get Jaguar to look at it, and would like to know whether it’s ok to run...
 
Phew! :D
If the level is correct when cold it suggests no coolant loss and you would think the circulation would remove any air pocket.
Does the heater work well?
The only thing I can think would be when the thermostat opens it clears an air pocket in the heater, so the level goes down when the coolant gets warm - inverse of what you would expect.
Difficult call and I’d be carrying a bottle of distilled water and ensuring that the temperature gauge stays spot on to the middle.
If you have Jag Assistance I would give them a call and explain your concern to drive the car - they should be able to do a simple pressure check and some visuals.
Let us know how you get on and what you find.
 
@AL1
Usually the coolant expands when hot. On my f type, when the coolant is on the MAX line when cold, the coolant level rises just into the black top part (non see through) of the coolant tank when engine is hot, so that you cannot see the actual "level" line, but if I grab hold of the short cross brace between the top of the suspension and the bulkhead and shake the car it moves the coolant about enough to show the coolant level where the see through part of the coolant tank meets the black top part. I wonder if this is what you are experiencing with your car, although I have not ever noticed any hissing sound on cooling. Also another thought have you checked the coolant filler cap has been tightened correctly? It has to be tightened until 3 "clicks" are heard from the ratchet in the cap, which is quite tight.
 
Actually that’s a good point - before my expansion tank was changed under warranty the car came back from a service with the cap ratchet broken.
The click is when it gets to a certain tightness - the following 2 don’t tighten it more but merely confirm the first one - if you feel the urge you can click it 5 or 6 times and it gets no harder to turn.
I had them send me a new one overnight in the post - there are 2 pressure variants I think so be sure to change like for like if the ratchet is broken.
 
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