1.9TDi (AFN) coolant loss - poss head gasket failure, opinions required

[JohnC]

Hi all

My A4 is losing coolant and I'm not sure why. I've searched this and the other forums exhaustively and read plenty of similar stories, but none are quite the same and it seems that people seldom update their threads once they've got sorted. So, I'm asking for help!

Car is a '98 1.9TDi quattro Sport saloon with 185k miles, AFN engine. I'm doing between 350 and 450 miles a week and I'm having to top up the coolant once a fortnight or so; it's usually one or two centimetres below the 'min' level so the loss isn't great but it's consistent. It appears to be venting from the bottom of the expansion tank as there are telltale splash marks below. When the engine has cooled there is still pressure in the tank and when I release it the coolant level rises slightly. The car is running perfectly normally, there's no white smoke on startup and there are no signs of contamination, i.e. no sludge in the tank and no mayo on the filler cap or dip stick. The radiator itself was replaced last August after it began leaking through corrosion.

The independent I use took a look at the car and this is what they found (taken from the invoice):

CHECK FOR COOLANT LEAK, NO EXTERNAL LEAKS FOUND BUT COOLANT BLOWN OUT OF HEADER TANK AFTER ROADTEST. BOTTOM RADIATOR HOSE COLD, SUSPECT THERMOSTAT. REPLACE THERMOSTAT & RUN UP TO TEMP, OK. ROADTEST AGAIN COOLING SYSTEM STILL PRESSURISING UP UNDER LOAD. SUSPECT HEADGASKET/INTERNAL LEAK.

As well as the thermostat they replaced the tank cap which made no difference either. I'm not convinced they really know what the problem is so I thought I should run these symptoms past the experts on here before I shell out on a head gasket replacement.

Just to confuse matters further, shortly after I started losing coolant I started finding it difficult to demist my windows. After researching this I discovered that a leaking heater matrix is the likely culprit, which could itself be brought on by pressure and/or air locks in the cooling system. My carpets are bone dry and there's no sign of there ever having been any water in the plenum chamber so I don't think the drain holes are blocked.

I'm not particularly mechanically minded when it comes to the business end of things but I'm willing to learn, so any opinions and/or suggestions from the experts on here would be most welcome. I assume I need to do a compression test next?

Thanks in advance.

 

[aragorn]

I would have thaught that a headgasket failure would result in steam out the exhaust, or some other signs such as water in the oil.

Not wanting to teach you to suck eggs, but have you removed the expansion tank and checked underneath it for cracks? Its not unknown for the bottle to crack then leak out when under pressure, but appear to seal up again when cold/unpressurised.

Its also normal for the system to be pressurised, to a point anyway.

 

[adamss24]

I would put me money on a craked head and not a blown head gasket. Head gaskets on diesel engines are multi-layered metal and as such, they dont blow/burn like the petrol ones. Vag group also uses stretch bolts wich hold the head tight to the block. I would check the water pump first/change if necessary as the impeller is made of plastic and its known to spin on the shaft but work fine at tick-over. If there is no oil mixing with water(mayonaise like) then the head might be craked between piston and water jacket. Have a decent garage do a compression test on the cylinders, any lower readings will point to a blown gasket. Cracked head will only show when the head is off and with ultrasonic equipment. Heads ussualy crack when daft owners top up with cold water on a hot engine. AFN engines were bullet proof in that respect. I would also check the bottom corners on the radiator as they known to rust and will weep dropping the coolant level. If the car does not overheat and there is still heat comming from the heaters then i would check/replace the radiator and water pump and pray for the best !

 

[jcb]

MLGaskets will burn and blow just like any others, especially with the massive compression in a DERV

I was always told "they don't blow for no reason".
If your thermostat, water pump or temp sensor is shagged then you can cook the engine enough to warp the head enough to exposing the edge to combustion heat.
You can get a blown gasket that just passes water from gallery to cylinder but you would normally see steam and water coming out the exhaust and not necessarily oil in the coolant.

coolant water changes colour and smell when exhasut gases pass through it, you can sometimes smell a rotten egg or slightly burnt smell to it,

I would check all the coolant pipes etc for leaks before you start replacing hardware or pulling heads off though

 

[JohnC]

Thank you both.

aragorn - no I haven't checked under the tank; I'd have assumed that the garage would've done this in their search for leaks but as always never assume! I'll have a look as soon as I can. Naturally we always look for water in the oil as a symptom of gasket failure but there's no sign of it here.

adamss24 - I forgot to mention it before but the car runs up to temperature perfectly normally just like it always has, and it's never overheated. Likewise the heaters work OK, no problems there. The radiator was replaced last August after it developed a leak; as you say it was rusted on one bottom corner. It was the original part - surely the replacement can't have failed already? There are no signs of leakage under the car.

Regarding the water pump, I've read elsewhere that they're supposed to leak by design. The car's due a cambelt change very soon so obviously I'll renew the pump then, and see about getting a compression test done in the meantime.

 

[JohnC]

You can get a blown gasket that just passes water from gallery to cylinder but you would normally see steam and water coming out the exhaust and not necessarily oil in the coolant.

Thanks jcb.

I get a tiny bit of white smoke first thing on cold mornings, but to me this looks like nothing more than the normal condensation you expect. Within a minute it's just the normal dark diesel smoke and there's absolutely no water coming out. Is white smoke from gasket failure more apparent when the engine is hot or cold?

 

[JohnC]

I thought I'd update this thread for the benefit of anyone with a similar problem who's searching for information (one of the biggest frustrations I found was that the majority of relevant threads just get left.)

My coolant loss continued at a steady rate until the last bank holiday on a trip down to Devon, when I finally saw oil in the header tank and the rate at which it drained increased significantly. Up went my temperature gauge, so down went my speed (a lot).

Thanks to a mate I was recommended a 'friendly' garage with whom (after some haggling) I agreed a decent price for all the necessary work plus a cam belt/tensioner etc. change, so I had it all done in one go. It transpired that the leak had occurred in the oil/water jacket and not the compression jacket, hence the gradual nature of the failure. Despite the contamination in the coolant, the oil was clean and free of water (I saw it myself) and the head itself was OK.

Since the repair I have covered nearly 2000 miles and not lost a drop of coolant. The hoses are pressuring up properly now; the car pulls marginally better than it did before and my fuel economy is improving.

I hope this is useful to anyone who finds themselves in a similar situation with an AFN.

 

[adamss24]

If you had a blown gasket between the oil and water ways then you should have oil mixing with the water...however, i suspect the gasket blown between the cyl. and the waterway wich pressurised the system. I still suspect a cracked head as these only show when the car is driven really hard but, you might be just lucky. I had a vw passat a few months ago with the same problems, all started with a leaky oil cooler wich would not circulate/cool properly due to oil/watter thickening. It then started blowing coolant pipes(the oil has weakened the rubber) and the only fix was a new head gasket and head rebuild. I could not see any obvious signs of failure on the head or gasket but the car is in daily use by one of my mates and runs better than before. It also over 250k and my mate has a really heavy foot- his other toys are a v8 motorcycle and a big block chevy v8 with a 6.2L engine...he also only manages 400 miles on a tankfull(motorway driving) !

 

[enriQo]

I thought I'd update this thread for the benefit of anyone with a similar problem who's searching for information (one of the biggest frustrations I found was that the majority of relevant threads just get left.)

My coolant loss continued at a steady rate until the last bank holiday on a trip down to Devon, when I finally saw oil in the header tank and the rate at which it drained increased significantly. Up went my temperature gauge, so down went my speed (a lot).

Thanks to a mate I was recommended a 'friendly' garage with whom (after some haggling) I agreed a decent price for all the necessary work plus a cam belt/tensioner etc. change, so I had it all done in one go. It transpired that the leak had occurred in the oil/water jacket and not the compression jacket, hence the gradual nature of the failure. Despite the contamination in the coolant, the oil was clean and free of water (I saw it myself) and the head itself was OK.

Since the repair I have covered nearly 2000 miles and not lost a drop of coolant. The hoses are pressuring up properly now; the car pulls marginally better than it did before and my fuel economy is improving.

I hope this is useful to anyone who finds themselves in a similar situation with an AFN.

Hi, first of all I hope that this thread isn't dead yet, although it's 2 years old... So I have a similar problem. (Might be, that the answer lais in this thread, but since I'm not a good english spoken man, I might haven't understood it.)
Things I have done:
1. Bought a car with a defective engine. (Head or gasket failure - spitting out oil from one of the air intake 'holes')
2. Bought used head (made a huge mistake and heavent checked it for cracks, before mounting it :/ )
3. New head gasket, oil - fuel filters, new timing belt, tensioners.
First start was a success! Everything seemed to be ok, only a little bit bad timing
But after 3 or 4 months car started to loose the coolant, and the main top hose that goes to the head from the radiator becomes very hard, I mean the pressure inside becomes very high. Now I have to refill and let out the pressure from the coolant container every 60KM! Actually I should do that more often, but since I have to go to work with my car I dont have time to stop every 100meters to do that. If I press accelerator in my rear window mirror I see a lot of white smoke (Road becomes like a disco with all that smoke/fog.. :/ ) So recently, actually yesterday I have changed thermostate (used one, but the man whom I got it from claimed that it's fine). Nothing changed, only the fact that before doing that, car temperature was 90 degrees or even in some moments after heating up the throttle, the temperatures was rising up to 95 - 100 and day before changing the thermostate it even was at the peak of 105 degrees!! :/ After the change of thermostate the temperatures became different, now after heating up the throttle it's even very hard to reach 87 (to open the thermostate atleast) :/ At idle it drops from it's now usual 70 - 75 to 60 or even below, since the gauge doesn't show less. But I get hot air blown out of a heater anyways...

Question is: What's the problem, what might be wrong..?

So after visiting some forums and threads I have decided, that I'm going to buy and replace the folloving (after about one week or so):
Water pump, brand new thermostate, temperature sensor, coolant ofcourse, head gasket (not sure if I have to change it), timing belts, tensioners (if I would have to change the gasket anyways).. So, if You understand what's my problem, please answer me as soon as possible..

 

[enriQo]

Hi, first of all I hope that this thread isn't dead yet, although it's 2 years old... So I have a similar problem. (Might be, that the answer lais in this thread, but since I'm not a good english spoken man, I might haven't understood it.)
Things I have done:
1. Bought a car with a defective engine. (Head or gasket failure - spitting out oil from one of the air intake 'holes')
2. Bought used head (made a huge mistake and heavent checked it for cracks, before mounting it :/ )
3. New head gasket, oil - fuel filters, new timing belt, tensioners.
First start was a success! Everything seemed to be ok, only a little bit bad timing
But after 3 or 4 months car started to loose the coolant, and the main top hose that goes to the head from the radiator becomes very hard, I mean the pressure inside becomes very high. Now I have to refill and let out the pressure from the coolant container every 60KM! Actually I should do that more often, but since I have to go to work with my car I dont have time to stop every 100meters to do that. If I press accelerator in my rear window mirror I see a lot of white smoke (Road becomes like a disco with all that smoke/fog.. :/ ) So recently, actually yesterday I have changed thermostate (used one, but the man whom I got it from claimed that it's fine). Nothing changed, only the fact that before doing that, car temperature was 90 degrees or even in some moments after heating up the throttle, the temperatures was rising up to 95 - 100 and day before changing the thermostate it even was at the peak of 105 degrees!! :/ After the change of thermostate the temperatures became different, now after heating up the throttle it's even very hard to reach 87 (to open the thermostate atleast) :/ At idle it drops from it's now usual 70 - 75 to 60 or even below, since the gauge doesn't show less. But I get hot air blown out of a heater anyways...

Question is: What's the problem, what might be wrong..?

So after visiting some forums and threads I have decided, that I'm going to buy and replace the folloving (after about one week or so):
Water pump, brand new thermostate, temperature sensor, coolant ofcourse, head gasket (not sure if I have to change it), timing belts, tensioners (if I would have to change the gasket anyways).. So, if You understand what's my problem, please answer me as soon as possible..

Update: Decided to solve the problem by changing the whole engine. Too much problems with the car are coming up, which led me to this decision. Anyway, I have noticed now for real, that this thread is totaly dead.