Coolant level going up and down?

Cosmo

Guest
Hello All,

The Coolant level/temp warning light and audible warning went off yesterday in my Mk3 Toledo. The engine was not over-heating but when I checked the level in the expansion tank, it was well below the "minimum mark". I topped it up with coolant to about 1mm below the "max" mark. When I first drove the car after doing this, I only got about 0.5 kms before I got the warning again. I pulled in, checked the level and it was back down well below the "min" mark again.

I drove straight home parked it. A couple of hours later I checked the level again and it was still below the "min" mark but this time I noticed that when I removed the the expansion tank cap to top it up again. The level immediately rose back up to just below the "max" mark. Does anyone know if this is normal and if so, how are you supposed to gauge how much coolant to put in?
 

Cosmo

Guest
That's normal. You should measure the coolant at cold, when there's no pressure in the system

Thanks for the reply. Yeah I figured as much but my problem is that when the car is cold the level showing in the expansion tank is below minimum. That's until I open the cap on the expansion tank, which causes the level to rise up to the maximum. So when I go to top it up the level is already at maximum. Therefore, I have no way of accurately gauging how much to put in.
 
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w1ll0711

Active Member
Jun 23, 2014
20
0
Cornwall
I would try changing your filler cap on the radiator, it works as a pressure relief at around 15psi, when the pressure hits this it vents the excess coolent (expanded liquid from heat) into the expansion tank via the relief pipe so if its seized shut the pressure cannot escape the radiator and system becomes heavily pressurised, the only way for it to escape is to go back up the feed tube when you tank the expansion tank cap off. Thats why the coolent level increases when you take the overflow cap off. Its the first (and cheapest) thing to check really. Hope this helps!
 
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