low coolant level. but no visible water leak.

[hammonds]

My coolant light came on while driving my Vr6 yesterday, i pulled over and checked my water and the tank was almost empty.  Filled it up and checked it again a few times since yesterday and the level seems to be slowly dropping.  I've had a look around the engine bay and under the car and can't see any visible water leaks (did see a tiny puddle which turned out to be oil, but i think my sump plug might need tightning).  Checked my oil and that seems ok, so don't think its a head gasket issue with water getting into the oil. 

[Adam]

Why are you ruleing out HGF? It could well be.

[MrBounce]

I had a similar thing with my 8v. It looked like it might possibly be a radiator leak (bottom right hand corner as you look at the front of the car) but just to be certain I changed the expansion tank cap. Cost me just over £4 and solved the problem.

Start cheaply first! 

[AudiA8Quattro]

After that, get the coolant system checked for exhaust gas.

[danp1383]

A dodgy rad cap was the cause on one of my cars. Sometimes they can be so small a really hard to spot especially if they are evaporating on the hot engine. I'd run the engine from cold and check all the joints/split hoses. I'd jack it up aswell to check around the back of the engine

Dan

[hammonds]

Was driving earlier, parked up for 5 minutes, went into a shop and by the time i came out about half a litre of water had pissed all over the road. Filled the tank back up, got it home and no leak.  had a little look around this evening letting the engine tick over for about 20 minutes, switched off and waited, no leak.  Apart from loss of water i'm having no other problems, oil temp is fine, coolant temp is fine and all my sensors seem to be working as they should be.  Checked my oil again, and that is fine, no watery deposits in there.

I have noticed one thing though. The expansion tank cap is usually tight on, as you'd expect. however the two times i have lost water big time and had to fill up, its been really easy to unscrew.  could it simply be that the cap is in need of replacing and that water is just over flowing from this?

getting it up on a ramp tommorow morning at a garage where our work vans get done, one of the guys there is into his VeeDubs so hopefully he can lend his view on it. 

[Wayne]

I would say your cap has had it.

[hammonds]

good job i've got a mk3 gti to test the theory.  Gonna switch the caps over, drive it to the garage tommorow, and see if i get much of a leak.  If it leaks, it probably isn't the cap.  If not at least i'll be at a a garage and can look for other faults. 

The joys of older cars.  Had my gti for a year 144000 miles, not much of a service history, sh!t loads of work done in the past. number of engine faults = 0.  Vr6, owned for 3 weeks, pretty much full service history, 94000 miles on the clock and water pissing everywhere (though apart from that small problem, drives like a dream). Still, all part of the fun.

[Wayne]

It could also be your head gasket building up pressure in the tank and then the cap is letting go.

[hammonds]

Just swapped caps, taken it out for a spin, and leakage, not much but coming from somewhere at the bottom of the engine.  Expansion tank cap is tight.  Could be the head gasket but apart from the loss of water i'm not getting any of the other symptoms you'd usually expect. Calling it a night for now and see what luck i have at the garage.