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Matt
Matt, Mechanical Engineer
Category: Audi
Satisfied Customers: 22907
Experience:  BEng hons Mech engineering, in auto industry 22 years
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my audi a3 is losing coolant, the car has a 1.6 engine is diesel

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my audi a3 is losing coolant, the car has a 1.6 engine is diesel has done 70,000 miles it is a 60 reg. a compression test has been done, there are no visible leaks (left sheet of cardboard under engine overnight) no sign of water in the oil, loss of coolant is 500ml every 200 miles help!
Hello


If you have a tiny pinhole leak in a radiator then these often don't leak water but will lose water as steam ( steam molecules being small enough to pass through the hole where liquid cannot) take a look on the rad for any signs of localised corrosion and for areas that look like they've been 'steam cleaned'.

If all of this is OK it may be worth replacing the header tank cap as again you can lose coolant as steam if this is blowing off too early ( the cap should hold pressure of around 1Bar)

The other thing to try is a head gasket / block test kit as these take a coolant sample and analyse it for any signs of combustion gas - if present this would indicate the head gasket is on its way out

http://www.uktools.com/block-tester-p-12508.html
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