Audi A3 TDi losing water

secret_tramp

My A3 TDi seems to be losing water - the coolant light comes on after about 10 or 15 miles.

I have run the car for about 20 mins with cardboard underneath and I didn't detect any water leaking from anywhere. Previously it leaked from two places because I had overfilled the reservoir.

A mechanic (ex Audi apparently) looked at the car and said the secondary cooler (an EGR cooler) needs changing as it is likely water is being sucked into the engine. He didn't spend much time looking aside from a cursory look underneath with a torch for a couple of minutes.

Another mechanic (who hasn't seen the car) suggested that the thermostat housing could be damaged (made from plastic) or the water pump is damaged (plastic propellor breaks, apparently).

Other forums suggest a heater core could be to blame.

Is there any reliable way to pinpoint what the problem is as I don't want to change water pump/timing belt or throw fortunes at the car unnecessarily?

Any advice gratefully received as I am finding this issue very frustrating and really don't know who to trust to resolve this properly.

CRH71

In all honesty, you might be better off taking the vehicle to a local independent garage and ask them to pressure-test your cooling system.

Given that you've already created an "overpressure" issue by overfilling it once before, it could be any one of a number of issues - from a loose hose clip, to a pinhole in a hose, to a knackered seal on the reservoir cap, to a cracked radiator, cracked reservoir and so the list goes on.

For the sake of what will probably be half an hour's labour at most (£20-25) the garage will be able to pressurise the cooling system with the engine switched off and see where the leak is coming from. You may not be able to see the leak with the engine running as it maybe leaking onto a hot part of the engine whilst it's running and instantly evaporating.

If it's a heater core problem, then by now I'd expect you to have a "sweet", sickly smell in the interior of your car by now, and/or complaining of the windows misting up on the wetter mornings. BTW - if it IS heater core, please be aware that this is a heck of a job on most cars, especially modern ones, and the cost will be significant. I helped a good friend change one on his Volvo 850 once and to say that was a "significant task" and "considerable work" would be a severe understatement - we ended up stripping out and removing the entire dashboard which included the airbags.....

For the low coolant light to be coming on after 10-15 miles is not a good thing - that's suggesting a water loss around a litre in that short distance. If the engine was drawing that volume of water in and burning it (nowt else it can do with it!) then you'd be complaining of running issues as well (the engine would be quite "lumpy") Frankly, my money's on a knackered hose/hose clip caused by previous over-pressurisation but I'm sitting behind a monitor, hazarding a guess, not sitting in front of the car with the cooling system pressurised and the engine switched off!

You could also try one of the widely-available sealants on the market, but view this as a strict "get you home" measure only, especially with a modern engine.

secret_tramp

Many thanks for your comprehensive reply.

For what it's worth, when the coolant light first came on, the reservoir had not been overfilled - though it has been several times subsequently.

The oil is not milky and so the head gasket has been ruled out.

s_b

secret_tramp wrote: »

Many thanks for your comprehensive reply.

For what it's worth, when the coolant light first came on, the reservoir had not been overfilled - though it has been several times subsequently.

The oil is not milky and so the head gasket has been ruled out.

wrong
i did a headgasket only yesterday
the gasket only went where it hit the water jacket so oil stayed clean

secret_tramp

If it was the head gasket would the car be overheating?

And just out of interest, how did you diagnose it was the head gasket?

poppasmurf_bewdley

Have a garage check the coolant with an Exhaust Gas Analyser. That will confirm whether your head gasket has gone or not.

s_b

secret_tramp wrote: »

If it was the head gasket would the car be overheating?

And just out of interest, how did you diagnose it was the head gasket?

it had a very slight miss

secret_tramp

Presumably that test would detect the presence of stream and the possibility that the secondary (or EGR) cooler is to blame.

But what to do first?

secret_tramp

Also...

The high level water being lost suggests the water is being burnt off, but the car runs perfectly and doesn't overheat.

I have been asked if there is any steam coming from the exhaust and I didn't really notice any earlier, but then again I wasn't really looking for any. So I guess I will explore that possibility tomorrow.

If there was steam, presumably water would be dripping out too? Or not?

s_b

have a pressure test and or a sniff test before you ruin your engine
its losing water

secret_tramp

Excuse my ignorance, but what is a sniff test?

And what does a sniff test establish?