Pressure in the coolant tank

[Rayscriv]

I've steadily been losing coolant over a period of months on my 1.9TDi Avant 115.
Over the last few weeks the problem has got much worse and appeared to be worse when the car is driven hard. I've had a good look and can't find any signs of leakage (I've researched several threads on here). I think the problem is that the coolant is being pressurized and forced out of the coolant tank.
I suspected the Head Gasket so my local mechanic did a pressure test and also a 'sniff' test. Both came back fine.
There is slight pressure if the car is ticking over for a few minutes but if the car is driven hard, even for a short period of time, the coolant becomes pressurized. If I remove the cap from the tank the coolant poors out of the overflow valve.
The heater still works fine, the oil / coolant doesn't appear to have mixed although the oil does smell pretty bad and steam comes out of the filler cap and dipstick after a hard run. There is no noticable white smoke from the exhaust and the car still has plenty of power.

Has anybody else suffered similar?

Can it still be the head gasket despite the pressure test and sniff test results?

Ray

[zollaf]

the sniff test is next to useless on a diesel. if the liquid does turn colour then yes, its conclusive, but rarely does it change. pressure test is also inconclusive as you put 10 psi into the system, yet to make it leak the cylinder has hundreds of psi available. so yes, could be the head gasket or a porous head. there is a test, you remove the manifolds then turn no.1 piston to tdc , put pressure tester on resevoir and pressurize system for 24 hours, then swop to the next cylinder, looking each time for any coolant on top of the valves.
what is your engine code. ?

[Rayscriv]

Hi Zollaf,
Thanks for the rapid reply.
In answer to your question re the engine code ........ I think its 85kw ????

[zollaf]

on the sticker in th boot floor next to the spare, there is a cde, like agr, awx, afn etc.... 3 letters. 85kw is the output power, which is presumably 115 bhp.

[Rayscriv]

Got it.... BKE

[Rayscriv]

Is that good or bad ????

[B5NUT]

Had the exact same fault on my 1.9 TDi 115 and it was down to a failed HG, I replaced it and it's been fine ever since.

[Rayscriv]

Good to hear B5NUT. I think i'll have the timing belt and water pump done at same time. The car has 160,000 on it but hopefully it'll give it aq new lease of life.
Just out of interest, can you remember what it cost you ?

[B5NUT]

Did it myself, so it was just the cost of parts like gaskets, head bolts, etc and I also did a few other jobs like what you have planed. Make sure you get a genuine HG

[Rayscriv]

Will do. Thanks for the reply.
I won't be doing it myself but my regular mechanic is a good mate of mine so I'm hoping it won't cost the earth.