My recently aquired Superb 1.9TDI 130 (AWX) has a cooling system problem that I'm looking for some advice on. Symptoms are as follows:

I do about 300 miles a week, and over this distance, it loses about 500ml of coolant. I've checked everywhere for leaks, and can't find anything. While looking for leaks, I noticed a lot of wet under the expansion tank (on the driveshaft and subframe), so suspect the coolant was being lost from the tank. I decided to tape some paper towel under the expansion tank and go for a blast up the motorway - after 10 miles, the paper was soaked with coolant.

I've tried changing the cap, and the problem is just as bad, so I've come to the conclusion that the system is overpressurising and forcing coolant out of the tank. The tank is still pressurised after the car has been standing over night (16 hours) - is this normal? When the cap is released, these is a hiss of air, and coolant shoots out of the top (narrow) hose back into the tank - would this be expected on a stone cold engine?

I also borrowed a prtable gas analyser from work, and sniffed the air in the expansion tank - it gave a reading of 10ppm carbon monoxide. This to me would suggest exhaust gases are pressurising the coolant, but where from? My first thought is head gasket, but then I read about the EGR cooler - does the AWX have one? If so, how do I tell which is at fault?

Any advice appreciated.

Thanks,

Dave

Head gasket, very popular on older 1.9TDIs.

Finally got round to getting the engine opened up last week. It had developed a horrible flat spot around 1500rpm, and was fairly gutless below 2000rpm. was also emptying the expansion tank on a weekly basis!

What they found was that the gasket had failed between cylinders 2 and 3, and the coolant had been tracking through between the coolant channels and combustion chambers. There was also pitting corrosion on the head surface in the same areas, and burning of the gasket from exposure to combustion gases. There was no obvious damage around cylinders 1 and 4. The only explanation thatthey can give me is that the head has been lifting slightly under load, allowing coolant and combustion gas to pass between the head and gasket. This has then caused the corrosion and burning that was found. May be that the bolts were incorrectly torqued by the factory, or they may have stretched over time.

Unfortunately, the corrosion on the head meant that it had to be stripped and sent away for a skim, which added quite a chunk to the bill! Had it pressure tested while it was away, and that came back all clear (no cracks or porosity), which is a relief. Valves and camshaft are also in excellent condition, which is nice to know.

Just got it back today, and there is a massive difference. The engine is much quieter and smoother running, the power delivery is much better, and it pulls like a train from 1000rpm now. I'll take it for a proper run tomorrow and see what the fuel consumption is like. The cooling system is also no longer pressurising excessively.

Hopefully that's it cured!

Edited 10 September, 201213 yr by daveholluk

Told you

So much for the 1.9TDi being bomb proof .

For what I've spent on getting this fixed, I could have bought a 2.0TDi, and had a new oil pump fitted .

Or, it would have paid for the extra fuel for a V6 for 18 months!

Well i'm kinda wondering why you didn't notice the faults before you acquired the car.. I would be amazed if there was no signs of this error when you got it.

Head gasket coolant leak on 1.9TDI is a gradually developing problem, and initially you can ignore it for months, I am not surprised seller got away with it.

1.9 was a good engine, but the compression ratio of 19:1 was a bit over the top. Nowadays most turbocharged diesel engines stay below 18, typically 16-17.

Or, it would have paid for the extra fuel for a V6 for 18 months!

I have the V6, and in the manual gearbox car this is the engine to have, 110k miles on the clock and I still do not plan to change it for another 50k - 130k. Keep in mind unless you do timing belt yourself (I did 30k miles ago), it is costly. Plus this engine has galvanic corossion issues, which basically means you need to spray a large part of its outside (injector housings, airco clutch front, a lot of various mounts and so on) with pure zinc spray to prevent rusting.

Edited 12 September, 201213 yr by dieselV6