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

On or around Thu, 20 Jan 2005 22:24:40 GMT, "Brian Tonks"
<[email protected]> 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.


--
Austin Shackles. www.ddol-las.fsnet.co.uk my opinions are just that
Too Busy: Your mind is like a motorway. Sometimes it can be jammed by
too much traffic. Avoid the jams by never using your mind on a
Bank Holiday weekend.
from the Little Book of Complete B***ocks by Alistair Beaton.

Not sucking the bottom hose closed is it?

--
Scott Forbes

"Brian Tonks" <[email protected]> wrote in message
news:[email protected]...
> 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
>
>

In <[email protected]> Brian Tonks wrote:
> 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.

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.
http://www.yorkshireoffroadclub.net/

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! )
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