Coolant Leak - TDI 110

[rwbaldwin]

Hi all,

I'm pretty sure I have a head gasket on the way out:mad:. However, I'd like a second opinion.

I'm losing about an inch of coolant every 70 miles but not all the time. Has got worse over last month or so. It started at about half an inch every 500 miles.

If I drive like Grandma (50MPH, 5th, No overtaking) I lose almost none.

If I really cane it (accelerating hard from 80 uphill) I blow the pressure cap.

The engine temperature guage stays in the middle (unless I blow the pressure cap) and the engine is not overheating.

I have changed the coolant expansion tank and cap.

I have wiped all the coolant pipes clean and checked for leaks.

I have inpected the radiator.

I have flushed the system and checked flow through radiator.

I have no 'eau de G12' smell or misting inside the car so I think the heater matrix is sound.

I think the pump is sound as I don't get any overheating under moderate/high load.

Fans are not on all the time - only as expected.

Thermostat opening as expected.

The system has been pressure tested but shows no leak (short term test).

A block test (for exhaust in coolant) was negative but this may be because the leak only occurs at high engine load.

No visible sign of head gasket leak.

No Coolant in oil or oil in coolant.

Any comments would be welcome.

[fordfan]

Have a very good look at where the plastic coolant housing attaches to the cylinder head on the passenger side of the engine.

[rwbaldwin]

Thanks for the advice.

I removed the hoses from the head coolant outlet so I could check for any sign of a split or leak. Unfortunately, it's not leaking from there.

[pikpilot]

On a different car with a belt driven water pump, I had the same symptoms due to a slipping belt.

This might translate here on the 110TDI to a broken water pump or pump vanes.

In any case, you should see a rise in water temperature just before the cap blows due to excess pressure caused by boiling. Hope this helps.

[rwbaldwin]

Thanks for the advice. I was aware that the pumps had a limited life.

The gauge doesn't creep up under heavy load. It just goes straight into the red when the cap blows.

I test the car on 1.5 mile stretch of dual carriageway that climbs all the way to the top. The cap blows about 3/4 the way up under heavy load. If I back off before I get to that point, the cap doesn't blow and the engine doesn't overheat.

I assume that under heavy load, exhaust gas is leaking across the head gasket and is over-pressuring the coolant system.

I'm just hoping it's anything but the head gasket - especially as I had the cambelt done recently.

[KenONeill]

An old fashioned solution to this sort of problem used to be to replace the pressure cap, on the assumption that the fault was a weak spring or seal causing it to dump coolant.

Is there any indication of there the "lost" coolant" is going? Wet or rusty coloured patches under the bonnet, or even under the car. for example.

[rwbaldwin]

Thanks Ken,

I replaced both the coolant expansion tank and cap as these are not usually tested in any pressure test. There is no leak that I can see or smell (heater matrix). The car has only done 91k but the head gasket has only done about 50k so normally I would say it is too soon. However, the monkeys who replaced it were also responsible for the engine falling out when then didn't replace the engine mounting bolts at a routine service. So, if it's possible to somqhow screw up, they probably have.

I'm just about to take it to my local independent mechanic so we'll see if he can find anything.

[KenONeill]

A coolant analysis didn't show exhaust gas in coolant: I'm confused!

[rwbaldwin]

It's definately the head gasket.

Just back from the mechanic and he agrees.

Did some tests.

After running hard under load, I caught it just before the cap was about to blow. Pulled over. The coolant was so full of bubbles that the level had increased by over an inch. Let the engine cool. Released the pressure. After running it for about a minute, the level was back to where we started - virtually no coolant loss.

As I said, the short engine was replaced at 40k. Just looked at the list of parts replaced - no head gasket!!!

[Kandy]

I don't think you could say 'definitely' HG.

(1) Redo the block test at the point of boil over to confirm exhaust gas in coolant.

(2) If none - look for another problem, lack of pressurization/circulation/blockage etc.

(3) If present - even then you could have a cracked/warped head/block. You need to test/fix each each part before reassembly - else you could be wasting money.

[rwbaldwin]

Oops,

I missed the block test result from the previous post. It went yellow almost immediately which confirms exhaust gases in the coolant.