overheating / pressure build

bad driver · Post by **bad driver** » 12 May 2004, 17:50

Hi my 306 td keeps overheating and spilling its coolant via the overflow. I have changed the thermo and checked all hoses for splits etc. I have also noticed however if I start the car from cold with the rad cap off the level rises quite sharply until it overflows. The coolant system has been flushed and checked for blockages but everything seems fine. I am concerned that possibly the head gasket / cylinder head is at fault here and is pumping gas into the coolant around the block /head and causing this error. Anybody know if this sounds feasible as there is no white smoke from the exhaust and the level doesnt bubble up as it would normally with this type of error.

macaroni · Post by **macaroni** » 12 May 2004, 19:41

Could be the head gasket, sounds likely, or could be a porous head. This happened on my 205td. It depends where the leak is as to what symptoms are observed.

bad driver · Post by **bad driver** » 12 May 2004, 20:16

the gasket has done less than 100 mile and I know it was fitted correct as I done it. The head was level checked for warping but not pressure tested for cracks, bit of a schoolboy error not having it tested I think. Anyway for now I have took the thermo out and it seems to of reduced pressure build up pending thermo opening so should hopefully retain coolant and let the degassing pipe do its job, just hope it holds until a new head can be sourced and fitted.

2ndtonunn · Post by **2ndtonunn** » 19 May 2004, 21:14

Try taking the car to a garage eqipped with a gas analyser, they should be able to 'sniff' the gas coming out of the filler cap and check it for exhaust gas content - at least then you will know the good or bad news!!
Glyn

Dave Burns · Post by **Dave Burns** » 19 May 2004, 23:54

The degassing pipe is only there to take air bubbles out of the coolant, it has no direct affect on the operating pressure of the cooling system.
Dave

bad driver · Post by **bad driver** » 20 May 2004, 14:59

^ surely if its taking the air out then it will reduce pressure as there is less content in the coolant system?

rossd · Post by **rossd** » 21 May 2004, 16:02

No because the system is sealed/pressuried, it simply moves the air to the expansion tank. Therefore the air is still in the cooling system, but above the water level in the expansion tank and not as bubbles in the cooling system.

andysautos · Post by **andysautos** » 22 May 2004, 04:02

hi, not definate on head gasket or head, as i have exactly the same problem i have replaced head gasket and had the head checked and skimmed, and i still have the same problem

bad driver · Post by **bad driver** » 24 May 2004, 23:31

Ok, I'm still puzzled with this. the gas out the degasser seems ok, just normal air from what can be checked. Also the rate at which the bubbles come out does not equal the speed at which the level rises. What also concerns me is if there is pressure building in the expansion tank as the level rises, surely this must be leaving a void somewhere elkse along the sytem? If its a sealed system then something somewhere is empty for another part to over fill??