I own a 1990 Audi 80. It has provided 5 years of excellent service. However during the past year it has started loosing coolant. I have to top it up about every 2 months. The rate of loss has suddenly increased during the last few weeks, to the point when the coolant light comes on, it now needs topping up about every 80 miles (the light will start to flash from this point) . There seems to be no leakage, the coolant colour also remains blue. I have taken it to my local mechanic, who thinks it is a cracked head gasket, but he is not sure so I am open to opinions.
Thank you in advance for your time and advice.
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What condition is the radiator in? I used to lose a centimetre a week (500 miles) out of the expansion tank over the past 6 months. The rad finally caved in a month ago - probably due to the hot weather?
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Shahab, if you need a new rad (or indeed any parts) for your Audi try www.eurocarparts.com/
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A head gasket failure will be highlighted by over-heating and possible mayonnaise effect on oil as the oil and water emulsify.
Check *all* hoses and items such as the oil cooler (on the top of oil filter) - also check heater matrix, although if this was leaking you should know. I would advise against radweld or others. For a rad try www.vwaudibreakers.co.uk
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You may have a blown gasket without any symptoms other than water mysteriously disappearing. I had pressure build up in the cooling system so had it tested and it passed a gas leak test both times, but I wasn't convinced. I finally noticed water seeping from the head joint down the block under the exhaust manifold and that was enough reason to take the head off, and the gasket had blown despite the garage's, "well it passed the test so it can't be that" attitude.
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Did your mechanic do a pressure test to check for a leak? If not , suggest you get one done. It may just be something simple like a minor hose leak, or what about a faulty pressure cap seal?
Hope it's something cheap!
Regards,
Mike
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Shahab,
A cooling system pressure test will show up a serious head gasket failure, but a minor leak which may be enough for the loss of coolant you describe is best identified by a chemical analysis of the gasses present in the cooling system, known as a "block test". The gasses in the header tank are drawn through a blue liquid in a vacuum chamber, and if it changes to green in colour it confirms carbon monoxide (a combustion gas) is present. If CO can go one way, coolant can go the other, indicating a gasket leak or porosity elsewhere in the head or block.
"Mayonnaising" will only occur if oil and water mix, not if water is entering a cylinder without damage to an oilway seal.
Any garage should be able to carry out a "block test" - the kit is available from most automotive factors such as Partco.
Regards, Adam
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That's the test I had done, with the blue liquid. I watched them do it on two separate occasions and it didn't change colour, but I had a blown head gasket. Go figure.
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Ash,
The "block test" with the blue fluid will only indicate a gasket failure where the coolant is escaping into a cylinder. If the coolant is escaping externally the test will be negative, but the gasket is obviously (visually) failed. It is not a test for head gasket failure in all it's forms, just for coolant entering the cylinders. Likewise, it will not pick up a gasket failure that allows oil and coolant to mix.
Regards, Adam
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Right. But I was suffering from a very overpressurised cooling system after a blast (not a problem when pootling round town). So I thought it was a coolant into piston (or vice versa) leak which the block test should have spotted, also no oil in water/water in oil. In the end I spotted a leak which made my mind up to take the head off and then I saw it was gone. I just assumed that they did the block test wrong/badly and never when there again (which was a bit difficult as it was a mate's garage!).
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check that you haven't got a crack on the plastic coolant reservoir - sometimes liquid can leak from the top where there is a sensor, and it drains down the side and dries up so that you don't notice the leak ...
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