legacycentral bbs

currently i have a small problem with losing water
i currently have no overflow tank bcos of my fmic routing
the rad cap looks pretty old 2
also the car has been up to the h on the temp a couple of times with a blockage in turbo water feed line and broken radiator but now have sorted that out

now i warm the car up to temperature and it overflows a little but goes perfectly fine
and when i stop all the water drain out the overflow line and ends up with no water in the header tank at all

will a dodgy cap do this?

You need an overflow tank. The motor heats up and coolant flows out of the motor to the tank. When it cools, it draws coolant back in. Since the expansion tank is the point where this happens, it is going to end up empty without an overflow tank. Use a soda bottle if you have to.

its probably a gud idea to replace the cap tho right?

As mentioned you need an overflow bottle. Sounds like the cap is working as designed. They don't often fail unless the seals are damaged. It's just a spring and a couple pieces of rubber. By all means replace it if you feel like it's old.

Coolant expands when it's heated - all liquids do this. In order to maintain a cooling system free of air bubbles you need an overflow tank to accomidate the coolant expansion and contraction. Old cars without overflow tanks were designed to have air in the radiator when they were cold to allow space for coolant expansion. Even if you filled them all the way up they would just spit it out on the ground till they reached the level they desired to run at.

GD

ok thank you