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heater problems


golfref
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I have a 2001 1.9tdi pd engine code awx. The heater blows cold when driven over 2500rpm. It is fine up to this engine speed and will blow hot again after a few mins driven at lower revs. Also there is a water loss of about a pint every 100mls.

So far I have changed the water pump, theremostat, flushed the engine coolant including the heater matrix.

I have carried out a pressure test of the cooling system, it holds 10lb sq inch for hours with no drop in pressure. If the car is left for about 12 hrs and then the pressure cap is undone there is still a little pressure in the system.

I am a motor mechanic with over 40 yrs experience and this is driving me mad because it is my wifes car! So you can imagine the amount of earache I am getting.

I am now :ffs: .

Anyone got any ideas?

Golfref

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Ive plenty of experience my friend and im afraid to say you will need to change the head gasket.......had it on a few of this age now. They do pressurize the system and will help you lose a bit of coolant due to expansion when pressure gets too much it will release it via steam at the cap, of which it is designed to do but will burn some of it as well as combustion gasses are in the coolant circuit. What does the top of your expansion tank look like?????

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Tidydubs, thanks for getting back to me. The expansion bottle is perfectly clean, no signs of oil or fuel. Also no sign of water in the sump. If I put the pressure tester on and let her run it takes about 1/2 hr for the pressure to build to 3-4 Lbs. I have also carried out a cylinder leakage check. So I can see no signs of the H/gskt being at fault. Having said that I work on all makes and models, we being a general garage come MOT center. I don't pretend to be expert on any particular make. So if someone has come across this very problem then I am most willing to go along with it.

Golfref

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Well based on what you have said here, there is only one way your system will pressurize up and and stay like that in the morning/12 hours later.The last one i did showed soot in the header tank as they left it for a long time, hence why i asked about your header tank.The other thing is mileage????

I do beleive on such an earlier vintage Passat they have a secondary coolant pump for the fuel cooler which is mounted at the lower drivers side.

I have an abundance of knowledge about these engines etc......im not just a forum contributor i work for a VW retailer.......Hence i know all their quirks and like to help people out that are a bit stuck. A head gasket block tester from Snap-On or any other make they are pretty much the same(the one with the fluid in it) should pick up combustion gasses but they are not full proof.....cylinder leakage tester will not show jack im afraid unless its a real major leak.

You will find only a slight part of the gasket has gone around the combustion chamber either block side or head with blow by into the cooling system ive seen it so many times. It will get to the point where it will be starting weird and rev up high on very first cold starting, then drop to idle not so bad in the summer but worse in the winter.

Its not the nicest job in the world and can be long winded given what you have to strip ie access to cam belt etc. I think you may have to consider replacing your head gasket.

All the best Tidy

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Tidydubs, I guess I am hoping against hope that it is not the gskt. As you can tell I am trying everything just to avoid the reality. If it was a customers car I wouldn't hesitate.

Thanks for your help

Don (golfref)

No worries my friend............dont prolong the agony eh?

Think of all the brownie points you'll score :cool:+++

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