2.0 TDI cooling problem.... Please help

[stanley1]

Hi guys, ok here is my issue. Ive had the car now for 3 yrs and its been basically trouble free until recent months.
First main problem ive had is my camshaft failed and needed replacing, while this was being done i also had the belt and water pump done 2k repair when i got the car back i noticed the water in the header tank was still dirty so i took it back to audi and they done another system flush and all seemed good (nice and pink). Next i took the car to an engineering specialist to have my oil pump balance shaft upgraded and the oil pump inspected (£800) after reading about all the oil pump problems this is something ive wanted to do for some time.
ok so problem now is that i took the car on a journey the other day and parked it for 5/6 hours and when i got back to the car and started it the 'low coolant' warning came up, i left the engine running and popped the bonnet and the header tank was nearly empty. Once i unscrewed the lid pressure was released and all the coolant came back into the header tank and the level was normal??? Drove the car home and all ok, its never overheated on me. 3/4 journeys more and cR seems fine. The coolant level seems different everytime i check it?? Last night i went out and low coolant warning again. Popped the bonnet released the cap and pressue and the cooland came back. This morning i went out to the car and when totally cold i popped the bonnet straight away to release the pressure and the coolant came back, i done this before even starting the engine.
the car is going back to audi for an investigation on wednesday but i love to know what you all think before the tell me what they think is wrong!!
Im in the habbit of releasing the pressure in the header tank before any journeys now, the heater seems to work fine too and i dont have any white smoke out the back. I really hope this isnt a head gasket problem but if it is will it be expensive??
Ive never had any problems with the cooling system before all the work and flush, airlock maybe??
Thanks in advance

[zollaf]

this is indicative of air in the system. it compresses and thus the level in the header tank drops. undo the cap, the airlock expands again and the level comes back to normal. they bleed themselves so air must be getting in somewhere so the obvious choice is a headgasket, although there are other options.

[stanley1]

Thanks for the reply zollaf,
update:
so i took the car back to audi for an investigation and they have told me that all the problems could be that the heater matrix is blocked now after all the flushes. To be honest ive only just noticed that the heater does work fine however i stopped the other day and left the car running for a few minites and the heater went cold, as soon as i increased the rpm a bit it started blowing hot again. Now everytime the heater is on when driving its fine but if i stop at a red light for a few mins its goes cold. Im guessing its partially blocked and water circulates only when the water pump is running faster. Audi have said that they dissconected the heater matrix and flushed that seperately when it was in last week.
The problem with the coolant level dropping in the header tank is much better although it is dropping but at a much slower rate then before. (Not done much driving yet though)
they have tested the head gasket and assured me that its fine.
audi have said that all they can do now is replace the heater matrix and the thermostat (expensive job im guessing) but can that really be causing the excess pressure in the cooling system?
just to make me more annoyed the car has also picked up a dent on the bonnet from the garage!!!! Not a big one but enough to annoy me greatly. Im not a very happy chappy at the moment, just want my car running perfect, after spending nearly 3 thousand pounds in the last 2 months that isnt too much to ask is it?

[zollaf]

head gasket blows water into system that enters matrix, causeing it to blow cold. more engine revs purge it out and heater works again. or, water pump is failing. either way, the heater matrix is not blocked and you are being fobbed off, try another garage.

[stanley1]

Ok, however this is all still related to the original work that audi done on my car. They may change the matrix and thermostat free of charge.
I diddnt have any cooling problems before the original camshaft and timing belt work. Water pump was also replaced at the time (2 months ago)
they tested the coolant for traces of exhaust gasses and nothing

[zollaf]

a diesel is very hard to test for headgasket failure if it is only slightly failing. they would have used a thing on the expansion bottle filled with a blue fluid that changes colour when exposed to carbon monoxide. if it goes greeen or yellow, gasket blown, stays blue, gasket ok. on a petrol it is almost 100 % accurate. on a diesel if it does change colour then gasket is blown, if it stays blue gasket could still be blown just not enough gas present to do anything. a blocked matrix will not cause pressure, and a stat will show as an overheat or overcool. could be the new pump they fitted though. i would leave it with them , get a courtesy car and not hand it back until yours is sorted.

[stanley1]

Thanks again zollaf,
i will pursue it next week with audi
im sure you obviously know a lot more then i do about engines mate
the problem is definatly better now though (not building pressure as quickly as before) so im scratching my head still.
surely if the gasket was leaking slightly then the pressure would be building just as quickly as before??
the level is dropping slower, maybe i can drive 2/3 times further now before its very low

[stevegrass777]

It could be the water pump,Audi/vw water pumps are only recon units and I would prefer not to use them.
I had a water pump gone and the impeller spins under load,so first I flushed the system and this improved the overheating,but every time I push it uphill it still over heated and pressurized.
The plastic impeller will spin on the shaft and you can feel play on the impeller if you take the thermostat out and feel around the corner to the impeller.
The over heating can cause pressure in the system.When the water pump gets really bad the car will over heat and blow all the water out of the tank.The lack of circulation could cause the heater to stop as the pump might work better under higher revs if its spinning on the shaft.
The heater matrix can be easily tested by taking both hoses off and attaching the hose pipe to one of the pipes,if it flows good its OK! end of.

The egr cooler can stop the heater working as its on the same circuit, you can test the flow in the same way or bypass it with 15mm copper pipe with 22mm ends on,I have done this with mine for now as it is leaking water into my air intake on the engine,and now my heater works.
If it does turn out to be the water pump you could claim all the works carried out and the water pump as it will have a 2 year warranty.
A blocked heater matrix shouldn't make the car over heat or pressurize to much it should just stop the heater working as it will stop the flow in that circuit.
A blocked radiator would pressurize and over heat but I doubt its that.

[stevegrass777]

Do you have any steam coming out of the exhaust? It looks like whispy smoke
If yes its the egr cooler.

[stanley1]

No ive not noticed any steam from the exhaust. Also the car has never overheated. Im going back to audi today to thrash it out. As mentioned above they should fix my problem and provide me with a car while i wait. This all started after the original camshaft work, when they also done the water pump and cam belt, its not right is it. Ive paid them a lot of money and my car has problems not that wernt there before!!
if i drive 30/40 miles the header tank is nearly empty until i unscrew the cap and all the coolant floods back. If i dont release the cap and keep driving then i get the low coolant warning. They need to fix this. What should i do if they dont agree to fix it free of charge?