Ready to put the sledge hammer to it..

Hi all, I recently posted a Blown expansion tank thread

I've replaced the tank, replaced the thermostat and replaced the water pump just to be sure I'm covering most angles... However, when I took it for a short test run (10k) it finished up overheating again. I completely replenished the coolant and topped up from the thermostat filling point - am I missing something??


(Pipes seem OK, but I've ordered a set of silicone which I'll replace as soon as they arrive.)

Which engine?

discovery tdi 300

They have got a bit of a rep for airlocks.

Never had one but seen suggestions of lifting expansion tank up and parking on a steep downhill slope to bleed.

Sure you've checked but could it be a blocked rad or rad return pipe. My p38 did a silly thing like that and it was because of a small bit of grit totally blocking the return pipe to the expansion tank.

I would agree with the above - you have a blockage somewhere - or the HG has gone big style, and is pressurising the system and blowing the coolant out...

Id clean the rad pipes and rad out. Or get a garage to test the coolant to see if head gasket has blown.

I had a similar problem, My road-car is a 1989 Passat with a tdi engine conversion, when I bought it the head gasket was shot (so I drove it home from Cheltenham to West Wales )
when idle / tick-over or revved out of gear the water level was perfect, when driven it was ok as well BUT when under load / boost it would blow the coolant out (I tried 'steel-seal' but it didn't work!!)

previous owner had changed the expansion tank as it had split!

after driving around for maybe 6 weeks with this inconvenience it let go properly & wouldn't start as it would hydraulic so I changed the engine as on passats its the same cost & easier than HG replacement


maybe you have the same issue (split head gasket 'fire-ring' / cylinder seal thinggy) and when under load / boost the water system becomes pressurised then vomits coolant on the road?

summint like that anyway

Rich.

I guess it could be head gasket... However, when I've had blown head gaskets on other vehicles,way back in the 70s& 80s I never had a coolant 'explosion' it was more a loss of power under load and quicker loss of coolant?


...and yes, zed, it seems like the same symptoms

I changed the hg on my 200tdi D1 last year as it was underpowered & smoky, when I lifted the head there were no obvious signs so I re-built but fitted different injectors & twas better again (luckily I have spares )

Rich.

Harold 4x4 said:

I guess it could be head gasket... However, when I've had blown head gaskets on other vehicles,way back in the 70s& 80s I never had a coolant 'explosion' it was more a loss of power under load and quicker loss of coolant?

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If the head gasket is leaking engine compression into the cooling system, you most certainly will get an explosion of the header tank, I have seen it happen on my mates Tdi when it overheated and then blew the cap right off and split the tank at it's midriff joint, lots of pressure. The cooling system is only designed for about 15 Psi, introducing 200 plus psi from the cylinder/cylinders, does not bode well for system components.
Fill the system then start the engine with the cap off the tank and see what is happening to the coolant in the header tank, someone told me when I bought my first Tdi home, "watch the cooling system, once the temperature gauge starts to head north to the red zone, it is already too late to save the head gasket", in other words there is no such thing a a mild overheat with these engines.

Harold 4x4 said:

I guess it could be head gasket... However, when I've had blown head gaskets on other vehicles,way back in the 70s& 80s I never had a coolant 'explosion' it was more a loss of power under load and quicker loss of coolant?


...and yes, zed, it seems like the same symptoms

Click to expand...

Depends how the gasket goes doesn't it?
If it fails between a cylinder and a water jacket then the cylinder will over pressurise the coolant system.

Yes, of course

I was simply trying to 'wish' it wasn't the HG...

Ordered a complete gasket set from JGS 4x4 and will get on it next week.