Losing water, but no leaks

[phil2580]

Hi,

I'm losing my hair quickly with this problem.

My 51plate TDi 130 (AWX) has started to lose water, but there's no leaks.

Took it to a garage who pressure tested and, no surprise, they diagnosed a leaking water pump. Got them to change that & cambelt, but problem still not fixed. Took it back to them where they did another pressure test on 100% G12, but still no leaks. They test drove the car and said coolant was being blown out of the expansion tank.

They then did a block test which showed the head gasket was fine, so recommended that the thermostat be changed. I did this, but the problem is as bad as ever. I lost 5 litres of coolant yesterday in about 30 miles, so its definitely going somewhere.

The cooling system is pressurising, and when I undo the expansion cap to top it up, the pressure releases and some coolant makes it back into the tank.

There's no obvious sign of a head gasket leak - oil is good, no oil in coolant and no steam out of the exhaust. I'm at a real loss on this one, but I've already spent the best part of £500 on the problem, and I'm no further forward. :zx11:

Help!?!?!?

[kenney]

Although you have no obvious signs of the head gasket leaking,it can still leak,and from what you have explained,and the symptoms,i would say you do have a leaking head gasket

[macquatic]

Although you have no obvious signs of the head gasket leaking,it can still leak,and from what you have explained,and the symptoms,i would say you do have a leaking head gasket
Agreed.
Block tests (sniffer) don't work too well on diesels.

[caldirun]

Hi,

I'm losing my hair quickly with this problem.

My 51plate TDi 130 (AWX) has started to lose water, but there's no leaks.

They test drove the car and said coolant was being blown out of the expansion tank.

the problem is as bad as ever. I lost 5 litres of coolant yesterday in about 30 miles, so its definitely going somewhere.

The cooling system is pressurising, and when I undo the expansion cap to top it up, the pressure releases and some coolant makes it back into the tank.

There's no obvious sign of a head gasket leak - oil is good, no oil in coolant and no steam out of the exhaust. I'm at a real loss on this one, but I've already spent the best part of £500 on the problem, and I'm no further forward. :zx11:

Help!?!?!?
Drive it for 2 mins then open header tank, if it is pressurised its the head gasket leaking (no way will the coolant boil in this time).
If coolant is being blown out of the expansion tank, head gasket is leaking!
Leak could be combustion chamber to cooling system, why do you expect oil in coolant or coolant in oil?
Steam is invisible, if you can see it its water vapour, not steam!

[phil2580]

Problem solved, and for less that 5 quid.

My expansion cap was faulty, so no pressure being released. Fitted new cap and have done ~500 miles since with no loss of water.

Will have to find a new garage now, the 'VAG specialists' I use have given a misdiagnosis both times I've been to them.

[caldirun]

Problem solved, and for less that 5 quid.

My expansion cap was faulty, so no pressure being released. Fitted new cap and have done ~500 miles since with no loss of water.

Will have to find a new garage now, the 'VAG specialists' I use have given a misdiagnosis both times I've been to them.
Should that be "no pressure being obtained"? the expansion tank cap will vent only on over-pressure if its working correctly.

[phil2580]

No, my original statement was correct.

The cap I had fitted when I was having problems was not releasing pressure when it should. It was too tight-fitting in the neck of the expansion tank, so would only let the excess pressure out when it was already way too high. All of my hoses were rock-solid when the cap was in place, so there was clearly too much pressure in the system.

[caldirun]

No, my original statement was correct.

The cap I had fitted when I was having problems was not releasing pressure when it should. It was too tight-fitting in the neck of the expansion tank, so would only let the excess pressure out when it was already way too high. All of my hoses were rock-solid when the cap was in place, so there was clearly too much pressure in the system.
The cap should release pressure only when you have an over-heating problem or exhaust gasses in the coolant. The blocked cap was telling you something was wrong, did you check what I said in my other post re pressure from a cold system?

[dazmac]

I actually had a Mk1 Golf gti that had this same issue, symptoms of a head gasket failure. I had the same result for the changing of the expansion tank cap, Im tempted to try this first on my 115tdi that is showing the same as described.

Have you had any issues since posting?

[johnloaderuk]

Problem solved, and for less that 5 quid.

My expansion cap was faulty, so no pressure being released. Fitted new cap and have done ~500 miles since with no loss of water.

Will have to find a new garage now, the 'VAG specialists' I use have given a misdiagnosis both times I've been to them.

Had exactly this on my wife's Passat. Luckily I'd heard the expansion cap could be the cause, so a few quid later all was fixed, and has been fine several thousand miles later.

[tony-1977]

I know this is an old thread, but I have the exact same symptoms with my 2003 Passat TDi. Going to change to coolant cap. But where would the coolant be going as there's no leaks? :/