overheating 1982 GTV6

alfettish · #1 (**permalink**) 01-08-2008, 06:56 PM

Hi,
I stopped at a service station yesterday and noticed that my coolant was leaking out of the overflow.
Drove home as I was 1 K away and it was boiling like mad.
Filled it back up with less than 4 litres of fresh coolant and it was full (presuming there was no water in there that's less than half its capacity).
Today after driving some more it was boiling again but only after I stopped. Put another 4 litres in and drove home.
Guage reads a bit higher than normal on highways and about 90 degrees celcius when in a bit of traffic.
Anyone know what's going on? I've checked the oil and water and cannot find signs of head gasket problems.
filling with half capacity might signify a blockage or an air lock.
Any idea?

sh0rtlife · #2 (**permalink**) 01-08-2008, 07:34 PM

are the fans working ok?..have you burped the air?....water pump on its way out?

alfettish · #3 (**permalink**) 01-08-2008, 07:37 PM

yes sorry, fans are fine. There is no way to bleed the system as there is no bleed screw.
Water pump is less than 10,000km old. Not ruling it out but it should last longer than that. And no visible leaks coming from that region.

**RAGs** · #4 (**permalink**) 01-09-2008, 06:47 AM

Radiator blockage possible? The fans may be fine but what of the radiator temp switch? Finally, what are the chances of a stuck thermostat?

This would prevent the heated coolant from getting to the radiator, but would still flow to the bottle.

With no signs of milkshake in the coolant, leaks, or this not being a relatively new rebuild that needed to be re-torqued, the overheating seems rather odd. Good luck.

SamW · #5 (**permalink**) 01-09-2008, 06:59 AM

Maybe the Ausie GTV6's are different, but on the US models there is a bleed screw right on top of the thermostat housing. Check the fan belt running the water pump and make sure it is not too loose and slipping. It is possible to push compression into the water jacket without the tell tale signs of water and oil mix, it puts air into the heads which just makes things hotter, might be worth doing a cooling system pressure test to see if you get air bubbles in the cooling system.

AR4me · #6 (**permalink**) 01-09-2008, 08:21 AM

You could have a faulty cap (as in unable to hold propper pressure - the Milano is rated at 0.8 bar if I recall correctly, not sure about the GTV6). If you have a spare try swap it.
Jes

alfettish · #7 (**permalink**) 01-09-2008, 01:23 PM

Quote:

Originally Posted by RAGs

Radiator blockage possible? The fans may be fine but what of the radiator temp switch? Finally, what are the chances of a stuck thermostat?

This would prevent the heated coolant from getting to the radiator, but would still flow to the bottle.

With no signs of milkshake in the coolant, leaks, or this not being a relatively new rebuild that needed to be re-torqued, the overheating seems rather odd. Good luck.

alfettish · #8 (**permalink**) 01-09-2008, 01:25 PM

Quote:

Originally Posted by AR4me

You could have a faulty cap (as in unable to hold propper pressure - the Milano is rated at 0.8 bar if I recall correctly, not sure about the GTV6). If you have a spare try swap it.
Jes

alfettish · #9 (**permalink**) 01-09-2008, 01:27 PM

Quote:

Originally Posted by SamW

Maybe the Ausie GTV6's are different, but on the US models there is a bleed screw right on top of the thermostat housing. Check the fan belt running the water pump and make sure it is not too loose and slipping. It is possible to push compression into the water jacket without the tell tale signs of water and oil mix, it puts air into the heads which just makes things hotter, might be worth doing a cooling system pressure test to see if you get air bubbles in the cooling system.

AR4me · #10 (**permalink**) 01-09-2008, 01:30 PM

I think you could be fine while driving (with a failing cap). Once you stop, then heat and pressure build. Speculative, but hey, cheap to try out

Jes

alfettagtv2000 · #11 (**permalink**) 01-09-2008, 02:40 PM

i was thinking the same thing as ar4me (radiator cap) but since i have not had experience with the gtv6 i did not reply. coolant overflowing (after engine is switched off) from the coolant reservoir usually indicates a defective radiator cap (that cannot hold the sudden pressure increase).
the cap is rated at 13 psi (90 kPa) (0.8-0.9 bar/atmos) (information sourced from cpcauto.com.au)

alfettish · #12 (**permalink**) 01-09-2008, 02:43 PM

Ok I'll give it a go. Thanks all.

sh0rtlife · #13 (**permalink**) 01-09-2008, 08:41 PM

even if theres no bleeder there you can use one of the sensors in the stat houseing area to bleed it

5yearplan · #14 (**permalink**) 01-10-2008, 05:55 AM

I've never had a car with a magical bleeding screw, I just run it with the cap off, and squeeze the crap out of both the rad hoses, while pouring coolant right in the radiator til, she boils over, and keep doing it til I think the bubble is out. Then I wait for it to cool off, and see if it needs more coolant, or go kick the crap out of the car til she gets up to temp and see what happens. My money is on the radiator cap, otherwise there may be a small leak keeping the system from being pressurized. Do a good visual inspection and start the car, and check the hoses to see if it is circulating properly. Your thermostat might be partially stuck. So at highway speed there is just enough air to cool the engine, but at a stop the fans cant keep up. But check the cap and hoses and try and burp her first.

alfettish · #15 (**permalink**) 01-15-2008, 01:56 AM

Thanks all, the new rad cap seems to have fixed the problem. Got a shiny red one!!