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Help I'm overheating

Ok I now think i'm stumped. I am running a 3.9 in a bobtail rangy and it continues to overheat, Just so you get a head start into the diagnosis I have covered the following.

It's full of coolant It's full of fresh quality oil Iv'e set the timming with a strobe It runs hot on LPG and petrol The thermostat opens correctly Compression test on all cylinders checks out ok There is no creamy deposit in the oil It is not running rich It will sit at idol and full revs not under load in the garage and stay at

1/2 on temp guage vehicle runs beatiful even when hot. Temp guage works correctly Header tank cap has been replaced with new pressure cap. There is no airlocks. Viscous coupling is near impossible to stop once hot.

but once itdoes go over 1/2 temp it pressurises coolant system and forces it out the header tank Can anyone shed any light other than I suspect either a cracked head or block. If so how can I test for cracked engine components.

Thanks in advance for any help.

Regards Brian Tonks Tonks4x4

Reply to
Brian Tonks
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On or around Thu, 20 Jan 2005 22:24:40 GMT, "Brian Tonks" enlightened us thusly:

[hot V8]

the one in my 110 used to do that. It continued to despite all faffing until I bought a new rad for it. This included all manner of attempted radflushing.

Reply to
Austin Shackles

Not sucking the bottom hose closed is it?

Reply to
scott

Have you checked that the radiator is getting hot all over rather than just hot in one spot (near the top hose) and that the top hose is getting hot ?

When the header tank pressurises and blows water out, is the water very hot ? Seems like a daft question I know but it might indicate if the pressure is coming from the water are from an "outside influence" such as compression from the engine.

Other than cylinder head problems and the old faithful cracked block syndrome that the 3.9s are prone to, it could be that the water pump isn't or at least if it is then you're not getting a very good flow rate. If the water in the headertank isn't getting hot then that suggests a poor flow rate.

A partially blocked radiator might also cause the problems, often shown by cold areas on the radiator (which can also be a symptom of air locks of course).

If the pressurisation of the system is more than you would expect for the actual temperature I'd suspect the head gaskets - a compression test won't always show up this kind of problem as the leak into the coolant system may be small and may only occur when the engine is hot/under load. A compression test doesn't really show these kind of problems unless the problem gets REALLY bad.

If the pressurisation is a result of the temperature then I'd be looking long and hard at how much water is actually circulating inside the system. Either the pump isn't doing it's job or you have a blockage somewhere.

cheers

Dave W.

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Reply to
Dave White

Two things to test before you get angry and spend money on it.

  1. check the bleed nipple and small rubber pipe in the middle top of the inlet manifold, assuming 3.9's have them in the same place as 3.5's
  2. give the radiator a good dose of caustic soda to thoroughly clean it out, as they suffer badly from blockages. Next do a pressure-check and if that seems OK, check that the water-pump impellor is not missing any vanes

Mark

Mark

2002 KLR650 C7, 1989 KMX200, 1981 PE175 X, now sold,but without memories 1971 Range Rover ( mostly in bits! ) remove_nojunk to reply off group
Reply to
Mark Gardiner

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