paul_james09 Posted September 17, 2023 Share Posted September 17, 2023 So I’ve got a slow coolant leak. Maybe topping up the reservoir an inch or so every 100 miles. Only seems to leak on longer journeys. Can’t see any signs of leakage no puddles or wet patches nor any pink corroded areas. Pressure test seems to hold pressure. No sign of coolant in oil, exhaust smell in coolant tank or white smoke from exhaust. What areas should I check next? What’s all the possible areas that coolant could leak internally? Car is a3 8p 2.0 170 TDI CFGB engine Many thanks in advance Quote Link to comment Share on other sites More sharing options...
Magnet Posted September 17, 2023 Share Posted September 17, 2023 Hello Paul, Sorry to hear of your issue. Dropping an inch in the reservoir in 100 miles is quite significant. Simple things first - try fitting a new ( quality) cap to the reservoir. Kind regards, Gareth. Quote Link to comment Share on other sites More sharing options...
paul_james09 Posted September 17, 2023 Author Share Posted September 17, 2023 Tried a new cap straight from Audi Quote Link to comment Share on other sites More sharing options...
Magnet Posted September 18, 2023 Share Posted September 18, 2023 Great! Knowledge of that could have saved me bothering. Quote Link to comment Share on other sites More sharing options...
cliffcoggin Posted September 18, 2023 Share Posted September 18, 2023 Is the carpet in the footwell wet? Does the car interior mist up excessively? Quote Link to comment Share on other sites More sharing options...
paul_james09 Posted September 18, 2023 Author Share Posted September 18, 2023 No moisture inside the cabin. I’ve lost probably 2 litres since the issue has started about 3 weeks ago. I have a feeling it’s either evaporating or being burnt up. Would that much loss being burnt in combustion have a noticeable effect on performance? Quote Link to comment Share on other sites More sharing options...
JMKC82 Posted September 18, 2023 Share Posted September 18, 2023 Hi Paul, 2 litres in 3 weeks is a lot of coolant, and what do you mean burnt up? In the cylinders? That would not be possible (in my opinion). My trouble shooting suggestion (with extra care of course), is to top up the coolant when the engine is cold. Get the engine up to temperature (90degrees) with the bonnet open. Because the coolant system is under pressure and at temperature, you should be able to see 'leaks' or 'steam'. You may want a second person to rev the engine as the water pump If you have an undertray, possibly remove that, as that could be catching the coolant? Again, be careful. Thanks, Joe 1 Quote Link to comment Share on other sites More sharing options...
cliffcoggin Posted September 18, 2023 Share Posted September 18, 2023 The water can not evaporate if the system is properly sealed. Nor can it strictly burn, though of course it may leak into the cylinders or air intake and be expelled into the exhaust. Either way the loss should be detected by a pressure test of the cooling system which you said "seems" to be OK. What pressure was the test done at, and how long did it hold pressure? What is the general condition of the engine and has it been correctly serviced? How many miles has it done? Was the water pump renewed when the cambelt was changed? 1 Quote Link to comment Share on other sites More sharing options...
paul_james09 Posted September 18, 2023 Author Share Posted September 18, 2023 I believe we tested it at 26 psi for about 20 minutes. Serviced every year by previous owner. I had the timing and water pump done at 75k I’m currently on 105k. No other engine related in the two years I’ve had it. Quote Link to comment Share on other sites More sharing options...
Magnet Posted September 19, 2023 Share Posted September 19, 2023 Hello Paul, Certainly odd, since any leak - external water pump, external gasket leaks, or internal leaks into cylinders , would result in a loss of pressure over a 20 minute hold. Having said that, it might be worth checking the water pump for shaft leakage after 30K miles of service before moving on. Kind regards, Gareth. Quote Link to comment Share on other sites More sharing options...
cliffcoggin Posted September 19, 2023 Share Posted September 19, 2023 Your pressure test is fine so no obvious answer presents itself. Have you opened the cooling system recently? Is the heater working? I am wondering if you could have introduced an air lock which, because of its expansion when heated, can cause water to be expelled from the reservoir. Air locks can be stubborn to get rid of. Quote Link to comment Share on other sites More sharing options...
paul_james09 Posted October 2, 2023 Author Share Posted October 2, 2023 (edited) Been into the garage. Didnt drop under pressure again. They’ve checked common areas including the water pump. Nothing visible. After a road test more leaking. They’ve put dye in the system and told me to go back in a week. After a little more research I’m starting to think ERG cooler as it’s not always obvious and can still hold under pressure. What would be the best way of testing this? Edited October 2, 2023 by paul_james09 Quote Link to comment Share on other sites More sharing options...
cliffcoggin Posted October 2, 2023 Share Posted October 2, 2023 It wouldn't be the first time the EGR has been the cause of water loss, though I am surprised the pressure did not reveal it. Quote Link to comment Share on other sites More sharing options...
paul_james09 Posted October 7, 2023 Author Share Posted October 7, 2023 So after the UV dye test i can’t see anything around the engine bay. But there is couple of drops showing in the oil when I take the cap off. Still a slow leak and I’ve probably lost a couple litres in total the oil isn’t milky or grey so it’s not all in there Quote Link to comment Share on other sites More sharing options...
cliffcoggin Posted October 8, 2023 Share Posted October 8, 2023 A few drops is a few drops too many, there should be none. That points to the EGR leaking its cooling water into the engine. As far as I know the only test is to remove the EGR and examine it. What concerns me about the EGR diagnosis is that the oil has not become milky or emulsified, which is what I would expect if a couple of litres of water had mixed with it. Quote Link to comment Share on other sites More sharing options...
paul_james09 Posted October 13, 2023 Author Share Posted October 13, 2023 Back from the garage. Ruled out the EGR cooler after that was pressure tested. Ruled out the heater matrix Been told to monitor how much I’m loosing at take back in a couple of weeks. Whats the next logical thing that should be tested/checked? Quote Link to comment Share on other sites More sharing options...
cliffcoggin Posted October 14, 2023 Share Posted October 14, 2023 If your garage is only repeating the pressure test it did a few weeks earlier, and which failed to reveal a leak, it seems it has run out of ideas. Time to take the car elsewhere. Did you or the garage investigate the possibility of an air lock that I mentioned three weeks ago? 2 Quote Link to comment Share on other sites More sharing options...
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