2.0L TDi overheating issue

[bobfrankish]

Hi everyone,
I wonder if anyone can give me a bit of advice. The problem is with my son's car, an Audi A4 Avant S line, B7, 2008 2.0L TDi, reg. ML08 UWY. car has been fantastic for 2 years we have owned it, now has 116K miles, I have never had to do any work on it and am not really familiar with the car or the engine. It suddenly overheated when driving on the motorway, then coolant low warning came on, managed to get the car home without serious overheating, topped up with coolant. car runs perfect with no coolant loss on short trips, but temperature gauge creeps up when driving faster on motorway. There is no real coolant loss, I have bled the cooling system (hole in top heater hose), but the heater still blows cold air. Temp. gauge does not fluctuate from normal at idle or after revving to 2000rpm for 3 minute intervals while bleeding the system. I have pressure tested the cooling system a few times to 1.1 bar and there was no pressure drop at all, it held full pressure for at least an hour. One thing I can say is that the coolant was filthy. Any ideas?

[Larhal]

This sounds like a blocked heater core for your heat issue. You can reverse flush it to clear it out. As for your dirty coolant, you should flush the cooling system with cleaner, then flush it out several times with water befor filling it with coolant and demineralised water. It sound like your cooling sistem is full of junk.

[bobfrankish]

Hi Larhal, thanks for the reply. Yes, our "to do" list is firstly fit new EGR valve, we have EML light on and diagnostics say EGR fault. Car is often in limp mode so needs sorting. Next is flush cooling system out as best as possible and check the heater core. Blockage is likely, first due to sate of coolant, second top hose with the bleed hole definitely has hot coolant to it under pressure (squirts out nicely when hose pulled back), bottom hose is stone cold. Could the blocked heater matrix be the cause of the overheat fault? As I have said, I have a lot to learn about this car and engine. I restore cars for a hobby, mainly BMW's and all petrol engines, I also restored a MK3 Golf Gti which I sold over a year ago now, so have not been on the forum for a good while. Crasher gave me loads of help on the MK3, I see he is still alive and kicking! Thanks again.

[pdlh]

Wonder if your temperature sensor is also faulty? My past experience of these sensors was when they failed they read the temperature too low, and showed to never heat up to 90 degrees, however could your's be knackered? and showing overtemp instead? might be some way of using a laser thermometer or VCDS to monitor the temperature?

[bobfrankish]

Thanks for the input. I had a day on the car yesterday and am now a bit further on, hence the new thread. Any help is much appreciated.