Hi I my expansion tank seems to get overpressurised (so releases cooling fluid) every now and then. I'm running a standard pinto 2.0 Sierra engine on a Tiger Cat, using the original Tiger rad.
tia

Have you tried a new cap?

don't you normally need a bit of air in there that can be compressed when everything else expands?

If it is totally full then doesn't the expansion of the water cause a problem?

Just a thought.

Matt

I am running what i call a sealed system , as the pressure cap blow off outlet is connected direct to my expansion tank(off a corsa) which is just over half full with coolant , even after a good rally type thrashing the cooling fan comes on but up to now no problems with the system.

Mike

Water expands 4% in volume from 20 to 100C, so do you have 4% of the coolant volume as airspace in he header tank.. You should have more room that this though, so say you need at least 8% or so air space, i.e 9ltr system would need at least 720ml of air space in the header, and would pressurize the system to 15psi or so when hot (i.e. the air space is half the size (310ml) when hot due to the water expansion), I guess you might want more airspace if you run a lower preasure cap?

I had the same problem, and the above appears to be my answerer.. I just removed some fluid to make a bigger air gap in the header tank (about 300ml).

I ideally need more air space, currently the header water level not much higher than the top of the engine, ideally I would have more head of water (i.e. higher header tank).. Also the heater pipes and choke thermostat are higher so also have a bleed to get the air out... The other option is a sealed system, with a two way pressure cap and expansion bottle.

I though I had a possible head gasket issue but this seems to be the explanation in my case.... If I over filled I would loose a lot of water from the preasure cap..

Dan

[Edited on 24/9/09 by Bluemoon]

[Edited on 24/9/09 by Bluemoon]

You could also have a trapped air pocket somewhere -- gas expands a lot more than liquid, drilling a very small hole in the thermostat valve plate can make it a lot easier for trapped air locks to be avoided.

When you add top up water to the cooling system it will always contain dissolved oxygen and other gasses that get forced out of solution as the coolant heats to near boiling point.

Of course as with almost every cooling system post I have got to add make sure you have a proper by-pass connection in place of the original heater pipe work.

^^ Yep, this is also a factor for me as the expansion I see is more than 4%, there is some air somewhere! Not a lot but enough to cause trouble when the engine gets really hot (i.e. just after stopping directly after a long motorway drive) hence more air space would be ideal.

Dan

[Edited on 24/9/09 by Bluemoon]

The cap is brand new and seems to work well as it releases pressure. The tank was filled up to minimum so I assume that I have enough head room. This situation only seems to happen when trashing so I assume that there is no air in the system.
So I guess it must be some kind of overheating under hard load?

Don't assume anything about the min and max marks... Work out the volume/measure the volumes, the marks will be for the original manufacture, for different engine witch is bound to have a different coolant volume???

Marks on mine our way out for the current setup...

Dan