Losing water....thermostat problem?

29th March 2010, 14:18

A while back I noticed I was losing water from the top of the expansion tank. I found the rubber seal was perished and replaced it. Now i find i am still losing water somewhere, I have no idea where.

The oil has no water in it.
The exhaust has no steam coming out.
No sign of any leaks.
System has been topped up and bled yet still goes down.

A mate said maybe its the thermostat.

How do I check this?
After a run today I took the expansion vessel cap off and it was full to the top (now I am gaining water, lol), but not yet bubbling over....could this mean the thermostat isnt opening? There is no back pressure from the expansion either

29th March 2010, 16:24

the thermostat is purely a mechanical device that restricts the flow of water, when in the closed position, in order for the engine to reach the correct running temperature faster. It has nothing to do with water loss, unless of couse, you have a leak around the thermostat housing area.
The expansion vessel will be full when the engine has been running, as the water expands with the heat, this is quite normal. The expansion bottle when cold will not be full and under no circumstances fill the bottle up to the rim. There are markings on the bottle to the indicate the correct fluid level when the engine is cold. If you are losing water then it may be from the fact that you arn't filling the bottle up correctly and that the water is then pressurised and blows out through the overflow tube.

29th March 2010, 16:44

Doesn't sound like you have a problem to be honest, just keep an eye on levels

30th March 2010, 02:01

Quote:

Originally Posted by grumpypants

If you are losing water then it may be from the fact that you arn't filling the bottle up correctly and that the water is then pressurised and blows out through the overflow tube.

Nope filled to the correct levels

Quote:

Originally Posted by viciousjello

Doesn't sound like you have a problem to be honest, just keep an eye on levels

Definately using water, no sign of leakage and doesnt look like head gasket. May just have to let this develop

30th March 2010, 16:04

How much do you lose? I find that the level is always a bit low on mine but then it does not go down from there and the car does not overheat. Slightly low level that remains in that position is not a problem to wory about matey