Random Overheating

[paulh]

Really hoping someone can shed some light on this.

A few weeks ago my Gal suddenly boiled up on a trip back from gatwick. GOt it towed and took it to garage next day. The car had a replacement head fitted last xmas. When they were poking round they noticed the water pump wasn't changed, so they did that and the stat, and all was well for a couple of weeks. Then the same thing happened. As I wasn't far from home I decided to wait till it cooled off then drive it home rather than waiting for another tow. On the way home all was fine. Took it back to garage, let them have it for two days, couldn't find anything wrong. Same thing has happened a couple of times. It boils up at any random time, could be first thing after warming up, could be after a day of motorway driving, I leave it to cool, let any pressure out of the system, top up any lost coolant, and all is well again.

I'm worried its the head again but would it not just overheat every time i ran it? Can anyone possibly think what could cause such a random fault?

 

Cheers

Paul

[Amarok]

Paul,

I had a frontera TD that did exactly the same same senario as you head gasket and water pump then later random overheat it was the Rad that was silted up i.e the muck at the bottom of the rad stays put 95% of the time then when you go over a bump it dislodges and blocks up a couple of cooler pipes this creates an air lock and BINGO overheat, New Rad never happened again :D , Also you can get the garage to do a test with the indicator flud which will indictate if the headgasket is 'weeping'

Edited September 6, 2011 by Amarok

[paulh]

Cheers for that. Garage have pressure tested the head and its OK so they agree the rad is the culprit. Fingers crossed a new one sorts it!

[Amarok]

I would put some money on it Paul

:D

[paulh]

Well, it didn't! Boiled over again within half an hour of me getting it back. So far its had a new water pump, stat, radiator, the head/block has been tested and came back ok. THis is really odd. Garage are now thinking it could be a crack in the header tank that opens when it gets hot, or a hose breaking down internally and causing random blockages.

[chrispb123456]

Paul

Try removing the small pipe connected to the top of the water bottle, remove the filler cap and direct the hose into the filler (you may need to extend the hose) run the engine at 2000rpm and observe the end of the pipe, a stream of coolant should be ejected back into the bottle.

If nothing comes out then the restriction in the hose is blocked you will need to clear this or fit a new pipe.

If there's coolant with alot of air bubbles which I suspect there will be then you have combustion gases entering the system.

If only coolant and the odd air bubble that's fine.

 

Also check operation of coolant run on pump? if this is not working it could cause premature head gasket failure.

[Amarok]

Well, it didn't! Boiled over again within half an hour of me getting it back. So far its had a new water pump, stat, radiator, the head/block has been tested and came back ok. THis is really odd. Garage are now thinking it could be a crack in the header tank that opens when it gets hot, or a hose breaking down internally and causing random blockages.

 

Radiator cap ?

[seatkid]

Alway best to check radiator cap first.

 

Double check they did actually change the water pump (maybe ask to see the old one)

 

Next time it overheats - before you switch off the engine check if the booster heater is operating - maybe its turned on and not switching off due to an electrical fault.

 

PD heads can develop microcracking - usually around the exhaust valve area, these small cracks have the characteristic that they only open up when hot so dont show up with pressure testing. Usually caused by remapping or tuning boxes running too much power. Can only be checked by removing the head.

 

Could also be blockage in cooling circuit, a pipe breaking up internally or incorrect mixture of coolants though this would give a consistent overheating sysmptom.

[paulh]

Just heard back from garage, still no change. Head is only about 18 months old, they tested it with something that changes colour in the water if a leak is present, all came back negative. Mechanic is now removing each pipe individually to see if anything is breaking down internally.