by Jim Archer » Mon Sep 17, 2018 2:00 pm
It is there to stop the coolant boiling off when the motor gets heat in it.
If you drive very gently for a short-ish distance it will probably be OK if you keep an eye on the level. Don't quote me on this if you boil it up mind.
The issue is that the motor has hotspots when running that are at much higher temps than the rest - exhaust ports and top of cylinder bore mostly - the pressure in the system does 2 things, it stops localised 'micro' boiling in use (the tiny wee bubbles of gas dramatically cut heat transfer to the coolant), but more importantly stops all your coolant boiling off when you shut off and the pump stops circulating.
Jim
Mk7 140 Jumbo - Vantunered.
289,000 and counting.