[Mk2] [Generic] Water

[blogsy]

If I fill up my water to the top then put the cap back on. Then drive the car 10 miles till it's fully warmed up, will the water still be full to the top once it's cooled down. Or would the pressure of the hot water have pushed out some of the water. Therefore allowing me to always add more each time. about a mug full.

[abovetherim]

There is an expansion tank that needs to have the right level in it. Then top up via the coolant neck and bleed from the dad and the heater valve in the trunk to get all the air out. Heater needs to be on hot to do this.
Once all bled and levels correct the coolant will expand and if the pressure exceeds the cap some will flow into the expansion tank. On cooling the system will draw back coolant from the expansion tank.

There are plenty of guides to bleeding the mr2 coolant.
If the engine is pushing excess coolant out it may be tired cap or head gasket issue pressurising system.

[blogsy]

Thanks mate, I have a 0.9 bar cap on there now but I also have a 1.3 bar one kicking about. Could I try that to eliminate the worn cap idea.

[abovetherim]

But make sure you have the level correct in the expansion tank and the system properly bled first.

[blogsy]

[blogsy]

Had a look today. I can see how the coolant will overflow into the catch overflow tank, but I cannot see how it is possible for it to suck fluid back through the cap. It's only one way.

[Pauln]

I'm a bit confused by this too.

Presumably when the water expands it puts additional pressure on the valve in the cap and opens it to allow water to pass into the overflow. But when that reduces sufficiently the valve closes, and I can't see how water from the overflow tank can then get back into the system when it cools.

I took the cap off my car today after it cooled, and the sucking noise as I did so suggested negative pressure but the level had dropped to a point when I would have expected water to have been pulled back in from the overflow if it really is a two way system. I may be missing something obvious, but at the moment can't see how this works, if it really is two way.

Paul