Overheating AAZ tried my best but failed.....

[mrnickmuss]

My 1991 Doka which had a reliable AAZ fitted two years ago. I knew I had a slight leak around one of the flanges on the engine and I was keeping an eye on the water levels.
About four weeks ago the temp warning light came on at the end of an half hour drive about a hundred yards from my house, so I coasted home.
The suspect flange which was had failed was then replaced water topped up and bled and I then drove it without any issues.
The water level needed topping up once. I assumed it was some air which I missed and had come through the system.
I have since been driving it daily without issue.
Unfortunately last week I took my eye of the temperature gauge and I over heated the engine.
I put my foot on the clutch and the engine stalled. I guess it was slightly siezed.
This time it was spewing out steam on the flange on the back of the cylinder head.
I had it towed home and have replaced the flange and checked for leaks elsewhere.
I then set about bleeding the system with cab heater on hot.
For some reason it continues to overheat and over pressurise. (It has blown a hose off)
I have changed the thermostat, (which I have since taken out and tested. I also checked the water pump by feeling inside the housing and the impeller seems ok and turns if I turn the pulley wheel) Of the three pipes which run from the water pump, two run hot and the third, which I assumes runs to the radiator is running cold.
The heater in the cab also runs cold.
I have even tried lifting the front by about 20 degrees to encourage the air to the radiator. The radiator is not getting warm. (externally it looks in pretty good shape)
I have also fume tested to check if the head gasket has gone, it seems fine. The oil is still black.
The water in the header tank when revving moves through, but with bubbles in and pretty quickly it gets hot.
I have bled the system via the radiator and header tank but dont seem to be getting anywhere.
Any thoughts would be greatly apprecited.
Thanks in advance

[Paul Weeding]

Does the rad get hot too?

[mrnickmuss]

I took out the thermostat today patiently bled the system and ran it up to running temp the rad got hot and The fan kicked in and all seemed to be ok. I then plucked up the courage to drive it up the road to my local garage and within a few hundred yards the temp climbed really quickly way past where it should be. So I parked up luckily a friend who is also a part time mecahnic and was tinkering on one of his cars was there so we checked the radiator for air.... nothing... he even tested the head gasket again... the test said it was fine. but the coolant system is pressurising really quickly and there is bubbles in the water. He believed it to be the head gasket but didnt understand the test! so I waited for a while for it all to cool down and limped home.
Arghhh!

[Oldiebut goodie]

Impeller come off its shaft?
Bubbles could just be super boiling water?

[mrhutch]

change the water pump

if it's still broken it's the head gasket

[mrnickmuss]

Thanks for your replies.....i dont think it is the water pump as when I took the thermostat out I could feel the impeller and by turning the belt slightly I could feel the impeller turning... So I guess it must be the head gasket?

[Oldiebut goodie]

If the impeller has lost its grip, as the coolant heats up expansion takes place and slippage could occur, also as the impeller has to move faster it takes more force to move it against the coolant thereby tending to force it round on the shaft. Did you heat up the impeller to engine temperature before seeing that it wasn't loose?
Also it is no good running without a thermostat - the cooling system hasn't a chance of working correctly like that!

It is strange that there are more posts about overheating AAZ engines than other replacement diesels even given that they require careful cooling planning.

[Oldiebut goodie]

Just read back the first post - no mention of the tank behind the flap filling up at all, is the darlek cap working correctly? If it isn't releasing the pressure the system will be over-pressurized.

[mrnickmuss]

I took the pipe of the expansion tank in engine bay and I can see and hear the darlek nozzle working.... I have booked it in with my freindly mechanic next Tuesday. I hate to admit defeat but handing it over to someone who has years of experince and who I trust I think is the best way forward...
I will report back as soon as I know more.....

[mrnickmuss]

Bad news.... The head gasket has failed....
My mechanic ran it up to to temp and confirmed with a third fume test that it had in fact gone. (previously the test didnt show exhaust fumes we think as it was too close to the vaporising water so he used a tube and took a test further away and it showed up positive... Arghhh!)
My mechanic who I trust implicitly ( when I needed to replace my gearbox in December and I was pretty skint he let me use his garage and ramp, do the bulk of the work with him supporting me along the way then charged me a pittance) Told me that In his opinion I should be looking for a new engine, as he believes although the engine sounds OK, I could have damaged it beyond just the head. He went into detail why, Unfortunately I kind of glazed over, as all I heard was knackered engine.... I think he said...." it is pressurising too much and is not loosing water when not running, so he believes the water sleaves could potentially have dropped or distorted marginally not enough to leak water into the oil , (as it is still black) but enough to build too much pressure when heated....
My question was how can you know that it has done further damage..... ?
He said you can't unless you strip the engine or have xray vision...
So I guess my options are:
Get the head off and see what issues are hiding there.
Then replace the head gasket and cylinder head if required, then run engine to see what happens. (but the issue isthat I might be throwing hard earned money away....
So the next option is...
Look for a good replacement AAZ (hard to find)
Or finally go the TDI route...... (expensive but would have a great mechanic to help!)
I have an AAP box in and am running 215s x 80 15s so I guess any of the above is possible so its desicion time....
Any thoughts much appreciated!

[MGP]

It cost little if anything to remove the head and look, if the bores are scored then it's rebore or replace, if the bores are good then it is almost certain that the heads cracked the last head I had crack tested and skimmed cost around £70 so not a huge amount of money if you are uncertain when looking at it, new heads are available.
If your bores are OK then the cheapest way forward would be a new head (a second hand one would be cheaper but it's a lot of work to find out the replacement is no better than the one you have) than going tdi.

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[ELVIS]

Scratches had a brand new head the daughter keeps trying to sell me when i go in there

[mrnickmuss]

I have gone the replacement engine route... However I am looking forward to getting the old engine on the bench with my 10 year old son and finding out what was going on inside and hopefully we will learn a bit along the way!