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mike_a_mechanic, Mechanic
Category: Audi
Satisfied Customers: 5471
Experience:  17 years experience as a auto mechanic, foreign and domestic.5 years running my own repair business.
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I have an 06 plate SLine 2.0TDi A6 Avant Auto with 143,000

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I have an 06 plate SLine 2.0TDi A6 Avant Auto with 143,000 miles on the clock. About a year ago I had to have the heater matrix replaced as it was leaking coolant in to both foot wells.

Over the last month or so I have been having to top-up coolant bottle with 2 litres or so every day - say 40 miles. There is no obvious sign of a hose or anything else leaking from the engine. The car is not over-heating. There is no wet carpets or signs coolant leaking into the car interior. There is no emulsification of the engine oil. There is nothing unusual about the exhaust - no white smoke, steam etc. Any idea what the problem is likely to be and the best steps to check further?
Hi,my name is XXXXX XXXXX I will assist you with your question.
Hi with this type of issue where the coolant can not be seen leaking and it's not obvious where the coolant is going,the first step is to be a coolant system pressure test. You can normally rent these pressure testers at a parts store. The pressure tester applies pressure to the system and the weakest point will show itself. From what you are describing this sounds like the heater matrix again leaking and the leak has just not made it to the floor yet.
Customer: replied 5 years ago.

I agree about pressure test and will get this done. However, I am surprised you say heater matrix again - 2 litres a day for a month is a lot of water to just go missing without wetting any carpets. What about the other likely issues? e.g. head gasket? porous head? EGR cooler?

The only other way this amount of coolant can escape without a leak and intermixing with the oil is out of the exhaust which would indicate a head or head issue. This is also very easy to check. Using a block tester which is used directly at the radiator or overflow bottle,the block test is a liquid and it starts out one color and if the color changes the system has excessive amounts of hydro-carbons in the system and the only way that can happen is a failed head gasket,head,or cracked block. The head gasket of course is the weakest point. Also keep in mind the oil and coolant does not always mix when the head gasket fails on these vehicles.
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