Hi I am new to the forum and i have a problem with over heating of my '94 Discovery.

I have been unable to pin point the problem but I have bought a few parts along the way!

1. electric fans not working - replaced
2. advised expansion tank was shot - replaced
3. new tank split - cheap non genuine - went back to old tank (which is better quality non genuine) with 2nd hand GM cap.
   
   Seemed to fix it for a bit!
4. Took truck to radiator specialist - flushed system checked thermostat. Told all ok.
5. Boiled before I got home with it!
6. Specialist advises Viscous coupling is shot.
7. buy Viscous coupling myself and avoid $200 installation fee!
8. Refill system with new coolant and bleed over a few days - thanks for the hints!

All seemed okay but tonight i drive for a bit longer than usual and up goes the temp gauge!

So I am at a loss.

Do i trust the GM cap - seems to pressurise okay but a can hear it slowly sucking air when it is cooling. Is that right?

Is the new Viscous coupling okay - it doesn't seem any better than the old one. It blows air but should I be able to stop it when the engine is over heating at idle (I used an old paint brush on it to slow and stop it)

Should I trust the "specialist" about the flush and thermostat check.

The radiator is original - 15 years and about 170,000 km (100k miles) on the clock. The truck has had a relatively easy life with light off road (fire road & beach) and no wading.

Any help is greatly appreciated.

Nick.
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If you can stop the fan when it's over heating than you viscous coupling isn't doing its job and engaging the fan.

Get a new pressure cap that you know isn't leaking.

 

So, you pressure test the system for leaks, then do a chemical block test to verify is you have a head gasket failing.

 

You should not hear the suction through the GM cap, get the correct one.

 

Thanks for the replys.
I'll order a new cap - no one carries stock!

Mike, is the chemical block test a C02 test? I got that done when the expansion tank split - it came back negative.

Is it worth my while flushing the system myself? And maybe taking the thermostat out for a while?

I have to travel on Monday (OS) and when i get back in 2 weeks I am supposed to be taking my family camping - Not without the disco I won't. So I'm looking at thing I can do this weekend to get it done.
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As a short time fix yes you can remove the thermostat.
If your radiator is clogged it wont help that much to remove the t-stat.
I am thinking that you were sucking air (like you said) and you had a air bubble in the system.

 

Radiator is plugged or rotted. I just replaced mine.

 

Well I took the thermostat out.

Do you think I could get it to open in boiling water? So this "specialist" radiator repair guy has dudded me?

I put it all back together (without the thermostat) and took it for a decent run of about 20 miles stop start in traffic. Woohoo it kept it's cool!

When stopped in traffic I could hear the fan gaining power to keep the engine cool. So the viscous coupling is also working.

At no time did the electric fans come on, which is also good.

I'm thinking that the engine would heat up and gradually increase the coolant pressure until it blew, but the viscous coupling's bi-metal was still cool as was the radiator so the engine was getting no help from either.

Anyway I've order a new cap and thermostat. So it looks like I might be right to go!

I just need to decide whether I let this guy get away with it. LOL

Thanks everyone.

Great Forum.
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Thank you for posting what you did to correct the problem.

 

No worries Mate!

Next is the Cruise Control.
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