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Coolant level will vary depending on the temperature and the pressure within the cooling system. It is quite common for the coolant level to go up when the car is warm and drop when it is cold. Basically as the coolant warms up it expands (it's called an expension tank remember? ;) ), the car responds by adjusting the pressure in the system (pressurised fluids have a higher temperature boiling point), up to a limit (the release point of the valve in the expansion tank cap).

So, as you can see there is quite a scope for a variance in coolant level. As a general rule we tend to say top the coolant up to the seam, but there is an upper and lower level marked on the expansion tank, are you still within the marks when the coolant is cold? If so, nothing to worry about.

If you have overfilled the system, it tends to find it's own level over time (fluid expands and overspills the tank through the valve in the cap). Only time you really need to worry is if the coolant level drops (particularly i the tank empties).
 

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Looks like I'm a bit late today, both Pete and Andy have mentioned not releasing pressure cap when coolant is hot. When coolant is cold there is no pressure to release - at least none that I've ever noticed on a fairly long list of cars through the ages.


Tess, relax today. Let it cool down overnight. Check level in morning before starting engine. If way too high you could try to remove some (PLEASE do not stick a pipe in there and suck it out) until it is on the seam. Then go out for a decent 50 mile drive with the hood down. Have a llok at the level when you get back but do not touch the cap. Next morning (or after at least 2 hours) check it properly and hopefully all will be OK.

Tess, abject apologies if any of that sounds/reads patronising - defo not intended, just a problem with written rather than spoken word.
 

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Discussion Starter · #6 ·
Thanks for replies
Before i had all the work done - new head - i used to have quite a lot of pressure even when cold - i wouldnt know if there was more when it was hot as i wouldnt be so daft as to take the cap off when it was hot :eyes:

I do understand that the coolant is pressurised as it has a higher boiling temperature. This i guess is what concerns me as i dont now seem to have the benefit of this.

First thing in the morning The coolant is showing as being about 1" above seam. Take cap off - no pressure and no difference in level. Before I had the work done even first thing and stone cold - if the level looked a bit low - I would take the cap off and would have quite a lot of pressure, you know, bubbling gurgling and the like and the level would often go up to normal.

After I left my original message, during my lunch hour, I drove back to work (1 mile away) the temp rose fairly rapid so I pulled into a layby and it was nearly to the halfway mark - I sat for a minute before turning the heater fan on - it went down like a rocket almost to the lowest - just on the gauge - any clues there - seemed a bit of a dramatic drop??
Tess
 

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tess200857 said:
Thanks for replies


First thing in the morning The coolant is showing as being about 1" above seam. Take cap off - no pressure and no difference in level. Before I had the work done even first thing and stone cold - if the level looked a bit low - I would take the cap off and would have quite a lot of pressure, you know, bubbling gurgling and the like and the level would often go up to normal.
I have removed my cap loads recently and when system is cold, I have never had a pressure release when removing the cap. I assumed this was normal Tess. Can someone confirm this?
 

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Broon said:
I have removed my cap loads recently and when system is cold, I have never had a pressure release when removing the cap. I assumed this was normal Tess. Can someone confirm this?
When coolant is cold there is no pressure to release - at least none that I've ever noticed on a fairly long list of cars through the ages.
I cannot confirm that but repeat my belief based on owning cars for more than 30 years - no heat, no pressure. Very minor hiss when removing cap but nothing like the release of pressure from a system at normal operating temperature.
 

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Sprinter said:
I cannot confirm that but repeat my belief based on owning cars for more than 30 years - no heat, no pressure. Very minor hiss when removing cap but nothing like the release of pressure from a system at normal operating temperature.
Thought so, so maybe you have nothing to worry about Tess
 

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Discussion Starter · #10 ·
Thanks again chaps - I guess im just checking it out and am seriously paranoid after all the trouble in last couple of months - I suppose i just have to get used to whats `normal` for my car now.

BTW - How long do other MGF`s take to get to normal running temperature?
I only have to go about a mile to work so often doesnt get there. But i would say on average takes about 2-3 miles at normal speeds - i never hammer it until the temp gauge is showing the normal running temp? Normal being just under the halfway mark for my car. Of course, I never hammer it at all really -being a girl and all:devil: And, should the temp rise much more quickly if you have the heater switched off? This happened yesterday and gave me a bit of a scare - soon as the heater was turned on it dropped down a lot
Tess
 

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tess200857 said:
... BTW - How long do other MGF`s take to get to normal running temperature?......
i never hammer it until the temp gauge is showing the normal running temp? .....
And, should the temp rise much more quickly if you have the heater switched off?
The water temp guage gets to "normal" pretty quickly 1-3 miles depending on when the car was last used and outside air temperature.

The guage to watch is oil temperature. The advice from others (which I stick too, mostly) is keep engine revs below 3k until the oil temp gets to 60 degrees which is generally 2-4 miles.

The water temperature will rise quicker with the heater control on cold as coolant is not flowing through the heater matrix (kinda like a raditor) only coolant in the engine is circulating so will get hotter quicker. The engine thermostat will also be closed as water only circulates to the radiator when a certain temperature is reached.
 
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