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Matt, Engineer
Category: Audi
Satisfied Customers: 21500
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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I have 2002 Audi A6 2.7T Quattro. I need some one who knows

Customer Question

I have 2002 Audi A6 2.7T Quattro.
I need some one who knows a lot about the head gaskets and head gasket sealers?
I have ALL DIAGNOSTIC Equipment and tools needed to do ANYTHING ON THIS CAR.
My issue/question is I replaced the timing belt component kit the plastic flange that bolts on to the thermostat was split leaking coolant. I don't really feel like taking the heads apart if I can seal it with the special high quality sealer. At first it would over heat immediately before using any sealer. Now, after using a full thing of 32oz bottle of K&W HEAD GASKET AND BLOCK REPAIR. An this is after flushing the system with a cooling system cleaner with the BG flush machine and BG cleaner. The Audi A6 Runs great there no miss fires ever! Even prior to adding ANY SEALER there was no misfires). I Then
Submitted: 7 months ago.
Category: Audi
Expert:  Matt replied 7 months ago.


a coolant leak doesn't mean that you'll need to replace the head gaskets

the modern gasket sealants are pretty good these days and I'd say you will be fine

if you have any concerns then I'd suggest to use a coolant test kit

like this

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

Customer: replied 7 months ago.
Added the sealer with the thermostat off... hoping it would seal it but now after I've finished the whole procedure. An let it dry for 12 hours bone dry. It over heats after an hour. I then did a test on each cylinder pressure test hoping one would be failing... they all are exactly @ 150psi in ALL cylinders... an I know the Thermostat is not failed after i installed it. Then filled it with it water let it idle and it over heated only after I drove it for about 20-30mins. tells me something else is leaking and i even checked to see if coolant was mixing with anything and nothing.
Customer: replied 7 months ago.
I performed a block test on it too and nothing. I pressure tested and pressure stayed between 15-18psi and even bled it correctly.
Expert:  Matt replied 7 months ago.


OK then lets assume that the block and gaskets are OK, especially if you've done the chemical check and its passed

I'd next replace the thermostat in the engine.

Whilst the thermostat is being replaced you might as well also reverse flush the cooling circuit (remove top hose to rad and use a hosepipe to push water into the engine until you get clear water out of the radiator hose) and top up with 30-50% fresh antifreeze. Also check that the small diameter bleed hoses that run from the top of the radiator and the top of the engine aren't blocked as this allow the air to vent back to the header tank automatically.

If you still have a problem then check that the water pump impeller / turbine isn't spinning on its shaft. You should be able to achieve this by removing the bottom hose from the engine and use a screwdriver or similar to feel for the water pump impeller blades, whilst your assistant turns the engine over by hand.

If you can stop the impeller with slight pressure from the screwdriver the pump needs replacing.

Also its possible the belt is slipping so its worth replacing its especially if the rubber ribs are cracked or it looks shiny on flat side of the belt - while its off check that the tensioner and other pulleys all spin freely the exception to this is the AC pump ( if fitted)

I'd also suggest ensuring that you've got all the air out of the system as this sort of episode can leave pockets of air trapped and prevent the coolant from circulating properly.

So check that the small hoses that run from the top of the engine and radiator that run back to the header / expansion tank are free flowing and not blocked

If these are OK then remove the tank pressure cap and run the engine from cold with the heater set to full hot

As the engine starts to warm, squeeze the large hoses running to the radiator to help displace any air - all the time keeping an eye on the level in the header tank, making sure it doesn't drop below the minimum and open any bleed screws built into the top cooling hoses - closing them off as soon as they start to gush water

Once the engine is up to temperature the tank should be quite full. Switch the engine off and leave it to cool

Then top up to the mark once its all cold and replace the cap

Customer: replied 7 months ago.
The thermostat is a fail safe style that opens up when it fails then resets when its cooled down. So after it overheats coolant starts to come come out of the coolant reservoir cap it leaks out all pressure after it overheats so I know it's something else that allows it Leak oUt The Reservoir??
Customer: replied 7 months ago.
It's Been bled correctly too.
Customer: replied 7 months ago.
It's will NEVER OVERHEAT at idle either it happens when you drive it and hall ass with it. Only.
Customer: replied 7 months ago.
Replace the cap even when it's boiling in the reservoir. The cap works since it bleeds off when it gets hot it's safety thing to prevent things such as the flange that connects to the reservoir from damaging.
Customer: replied 7 months ago.
I feel the issue is somewhere within the block.
Customer: replied 7 months ago.
I blew out the first thermostat flange when I was doing the first procedure without a t-stat.
Customer: replied 7 months ago.
The water pump is brand new too
Customer: replied 7 months ago.
I also did the timing belt and full component kit too. Which included a waterpump. FYI
Expert:  Matt replied 7 months ago.


if the system isn't throwing water out and the water pump was new then all this leaves is a lack of cooling capacity

so a blocked radiator either with low coolant flow or the grill area is blanked off where it shouldn't be

if the grill area is clear then I'd say the radiator may need replacing