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Audi Mystery Coolant Loss (been leaking for years)

Audi A6 2002 1.9TDI 96KW 284000 miles/455000 kilometers

Hello all! My car has been leaking coolant for years now, and might have been doing this for 100.000 miles now (160.000 kilometers), I just always topped it off with water or a mix with some antifreeze.

I would really like to fix this finally, I recently lost heat as well and it starts to overheat when I need power. It still is reasonable when I drive calmly on the road, but still not full heat and still with me needing to top the coolant off after every ride. Also, hills seems to hurt my cart immediately.

The time has come to change the timing belt, and water pump (just passed 60.000 miles/90.000 kilometers, hope it holds a little longer). I might found a cheaper mechanic that might do the head gasket for a reasonable price, but I really want to make sure it is the head gasket, since I don’t want to miss and keep fixing the car. I was planning to maybe just get the belt done and keep driving, or maybe throw in some coolant flush and coolant seal to clean the car and win some time for a while, but I found a reasonably priced mechanic for the head gasket (I would not be able to pay the second best priced mechanic, and I’ve been looking around for years).

So I was wondering if some people might be able to pinpoint the problem or at least rule out what it is not?

So far, I’ve been suspecting the following:
-head gasket -radiator -water pump -cap -hoses -EGR -cylinder -thermostat

I haven’t noticed any white smoke in the exhaust, don’t have oil in my coolant as far as I can tell, no coolant in oil, the system seems to over pressurize, but other than that I really haven’t got a clue, Audi tried a pressure test but they said it was inconclusive, though dad might have noticed some smoke coming from around the engine when starting the car yesterday, and I sometimes hear water “flushing” when shifting into lower gear or accelerating rapidly. The car has high mileage, and the leak has been there for a very long time.

Many thanks in advance!

Topping off coolant after every ride? Yep, it’s annoying now.

How much are you adding ?

I used to work with a guy that every day before we left work, had to add a pint or so of coolant, I never gave it much thought.

Until one day after work I watched him do it, he was filling the overflow bottle to the top.
He said he had to add the same amount every morning. I told him to check it but not to add any the next morning. The next night when it was time to go home, it was still about 1 pint low, told him not to add any, Kept that up for 2 weeks, never went any lower, He quit topping it off and quit losing coolant.

At 284K miles, I think it is time to completely rebuild the engine - especially if you are going to do the head gasket.

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Sometimes a pint after half an hour, often not making my destination before the warning comes up nowadays

I looked at an 05 a4 w/140k miles. Needed headlight/ fender. But drove fine. New tires. Seller wanted 500. Buddy said no-no-no. So I passed.

Your engine may have coolant circulating through the intake manifold. That’s one place you did not mention. My Chrysler 3.3L V6 engine had a slow leak in that area. I couldn’t see any external leaks, then I borrowed (actually, paid for, then reimbursed upon return) a cooling system pressure tester from a local parts place. Pumped it up and let it sit overnight. In the AM the pressure was down and I could see leakage at one end of the engine where the intake manifold rests between the cylinder banks. That area also showed evidence of past leakage - evidence I had ignored because it was always dry, though discolored, when I searched.

The gasket was about $20. The project took me most of a Saturday, guided by my Haynes manual and some Youtube videos specific to my engine. I would guess a mechanic would charge for about 3 hours, plus new antifreeze.

The pressure test and inspection are easy to do even if you haven’t done much car repair. Good luck and please let us know how it goes for you.

Inconclusive . . . ?!

It either passed the pressure test . . . or it didn’t

Is it possible this “flushing” noise is inside the car . . . ?!

If so, your heater core might be leaking

The guy has a 1.9 liter TDI . . . sounds like an inline 4-cylinder. While I guess it’s possible, I doubt there’s coolant circulating through the intake manifold

I can’t imagine why you’d want to heat an intake manifold with coolant if it’s port or direct fuel injection.

There is a chemical you can add to the cooling system that can detect exhaust gasses in the coolant. There is I think another test that can also detect exhaust gasses in the cooling system as well. There is a simple test of just looking into the radiator with the cap off and the engine idling looking for bubbles in the coolant. The last is not a definitive test but since it is free, I’d do that.

You can also get a UV dye from Amazon. You can get a HOAT coolant UV dye from most parts stores but if you use Dexcool in your cooling system, you need the one from Amazon.

Some turbo chargers use coolant for the center bearing and that could be leaking. That would be hard to detect because it is so hot, it could be evaporating before you would see it but there would be some steam around the turbo. Also the coolant could be leaking into the intake air stream through the turbo and you would never see that.

Before assuming the problem is the head gasket be sure to do the applicable tests first. Replacing a head gasket it expensive, and ou don’t want to do it unless that’s actually the problem. A cooling system pressure test is the place to start, and relatively inexpensive. One test you could do yourself with a helper, warm the engine to normal, then accelerate as fast as is safe up a freeway on ramp while your helper follows behind. Any white smoke out the exhaust pipe then?

Are there any wet spots under the car in the morning? Sometimes coolant will leak only as the engine cools off.