Coolant Loss on Passat Pd130

[Fat Audi 80]

Strange one this.

My passat is intermittently losing a lot of coolant. It iwll be okay pottering around but any fast driving loses up to a litre in 50 miles. I have been through 10 -15 litres of coolant over the last few months...

On investigation, it appears to be coming from the high pressure / overflow on the coolant reservoir (Recently changed along with the cap). The cooling system has been pressure tested and lasted 45 minutes on a leakdown test.

The car does not overheat and runs perfectly, however the temperature gauge reads either 50 (bottom of gauge) or 90 degress.

The mechanic has suggested changing the thermostat next , but I could have a head gasket problem. Could a dodgy thermostat mean the coolant temp sensor being starved of coolant so that it reads cold?

Also the top coolant pipe is under a lot of pressure and fairly solid.

Car has full service history and is on 140,000 miles.

Any offers as to what is going on???

Thanks,

Steve

[s2driveruk]

http://www.s2forum.com/forum/showthread.php?t=10257&highlight=audi+a6+coolant

[s2driveruk]

could also be a faulty cap - can you see where the coolant is escaping from? there will be a tone of white scale splattered around the engine bay where its burnt/evapourated off.

When mine went for the second time and was pressuring the circuit....the coolant header was oily....when it was ingesting coolant (original internal HG failure in above link) no sign of issues

[diesel des]

Sounds like headgasket to me..

[simon20vq]

First you would have thought clouds of white smoke if the head gasket was gone? Is the water pump ok? the pumps have a plastic propellor that comes lose and although they appear fine there just doing nothing to cool the engine. Water could be pressurizing and then spewing out when hot

[Fat Audi 80]

Water pump was done recently and has been checked. Engine does not appear to run hot...

[SteveH]

I had exactly the same thing happening on my B5.5 1.9Tdi a few months back. It would be fine for weeks and then I'd come back to it and the level had dropped considerably with no obvious signs of a leak apart from coolant on the floor under the car. In my case it was the coolant hose that runs around the side of the head under the fuel filter and connects to the rear of the head under the inlet pipe. The rubber hose had turned to mush and it had a fairly large hole in it. I still can't see how it lost coolant some of the time and not immediately after refilling

The hose was about £15 and took about 30 mins to fit. The car has been watertight since.

Good luck finding you leak!

[Fat Audi 80]

Thanks Steve. The garage did a leak down test and it held pressure for 45 minutes. I am hoping a thermostat change on Monday will fix it, if not it may be a HG....

[kulster]

If you cannot see any leaks its the Egr cooler, done loads at work, take it off and if its wet it needs a new one. we found this out after doing headgasket, expansion tank ets on 1, the rest of them its now the first thing we check.

[baltiboyS2]

Thanks Steve. The garage did a leak down test and it held pressure for 45 minutes. I am hoping a thermostat change on Monday will fix it, if not it may be a HG....

In a ideal world a leak down test should show something but that is not always the case i had a customers A3 2.0 Tdi in with coolant loss did the pressure test leak down nothing so i pressurised the system and went round every hose and a found a leak on the heater matrix hose's on the bulkhead when i moved it side to side (Go figure pressure should force the water out)

cheers Raj

[baltiboyS2]

If you cannot see any leaks its the Egr cooler, done loads at work, take it off and if its wet it needs a new one. we found this out after doing headgasket, expansion tank ets on 1, the rest of them its now the first thing we check.

Don't think the 1.9 130 bhp has a water cooled EGR 2.0 Tdi deffo does as that was the first thing i checked on the A3

cheers Raj

[chezz]

Could a dodgy thermostat mean the coolant temp sensor being starved of coolant so that it reads cold?
Steve

Yes!

[Fat Audi 80]

Yes!

Thankyou. The temperature gauge will suddenly kick in and when it does I don't *think* it loses coolant. I am hoping the thermostat is intermitent and changing this will cure.

It is going back in on Monday for the 'stat change, so I will let you know.

Thanks all for your input.

Cheers,

Steve

[chezz]

A dodgy 'stat will prevent any circulation around the rad/head/block so what is probably occuring with the temp reading? - reading cool, until the boiling fluids start to retreat and then reading high as the boiling fluids exit the head past the sensors .The only place the fluids can go at this stage is back out of the top hose and cooler fluid will enter from the header tank and replace it boil up and so on.Circulation is none existant in the rad/block and you are in great danger of seriously overheating/seizing the entire engine. Check the lower hose near the 'stat and if it is fairly cool after running the engine for a while, then it is a good indicator of your problem.
You could remove the 'stat and still run the engine.Test it while it's out and see if it is in fact jammed.
Remember a failed 'stat is potentially terminal for any engine.

[Fat Audi 80]

Well the 'stat had seized solid and has been replaced. However, the car is even worse now. It is practically undriveable on boost. The temperature goes through the roof and the low coolant light comes on. You can get it back down to 90 deg by grannying it and it settles down again.

The car is back in the garage today for a suspected head gasket failure, which I can only conclude allows combustion gasses into the water jacket when under boost pressure.

I have lost the car for a week and it looks like it will cost me upwards of a grand. The head will be going off for pressure and crack testing along with a skim if required.

Gutted, but it needs to be sorted.

Cheers,

Steve