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VZ Monaro GenIII overheated. Radiator Cap???

scrounga

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Hi guys, Just want to know if anyone has a better theory. On our way back from Melbourne to Canberra today we stopped to change drivers. Shut the engine down and when I can back from the dunny it had dumped a heap of coolant. There was no coolant trail and nothing under the car except where the coolant had be dumped from the over flow bottle. Thought it MAY be a hot soak so took it for a quick run further along the highway with a very quick rise to limp home mode. RACV arrived and topped up the coolant and let it idle for a while with no problems so I followed him back to the Holden stealership and the temp was perfect with the air con on for the next 5-7 kms. When I stopped to say thanks for the help I looked back at the car, which was still running, to see it again dumping coolant. Long story short got brought home on the back of a truck. So the following occured:
Gen III V8.
Only overheated when the car was stationary with engine idling or switched off. Probably/ maybe could have driven home if I didn't stop. To far to chance it.
Thermos were working fine and hard.
No sign of a leak anywhere. Engine bay and under the car bone dry except for passenger side front where coolant was being force out of the overflow bottle.
No sign of a blown head gasket as engine was smooth and powerful and oil clean. Nice smooth idle.
Temp normal (1/4) when sitting on 110km/h before I stopped the first time and after visit by RACV.
Had the coolant replaced at the last service and has already been to Melbourne and back since then.

Conclussion: I suspect the radiator cap as this is the only way coolant can get to the overflow bottle but the dealership didn't have one (insert comment here) so I couldn't try it. I will get one tomorrow and keep my fingers crossed. I have been told by my son that VZ's are known to have radiator caps that fail. I have checked mine and it's the original but looks OK but I am suspicious of it. Besides it's 7 years old so a new one won't hurt and it's the cheapest and easiest place to start.
Any ideas on my conclusion would be welcome.
Thanks in advance.
PS when/if I have fixed the problem do the Gen III's need bleeding like the 6's???
Stu.
 

imoore

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It was only the v6 that have rad cap problems.
Gen3 don't have a bleeder
It sounds like the thermostat is stuck and not allowing flow. Very easy to replace, at front of eng with 2 10mm bolts. Just make sure u put the bleeder hole to the top.
 

RiCeY

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Radiator caps do fail on the V8's, Ive been through a few in my car and yes they will fill the overflow bottle when they fail.

Doesnt sound like a thermostat issue at all.
 

scrounga

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Thanks for the thought. Checked the thermostat in boiling water and seems to open OK. Just got back from Holden with rad cap and thermostat and will try them both.
 

scrounga

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Thanks for the reply Ricey. I agree that it doesn't sound like the thermostsat but for the cost $9.70 for the cap and $38 for the thermostat which comes with a new housing (this was trade price from Holden) I decided to buy both as the dealer shut at lunch time. Just got back from a 50Km run down the highway and all is good. Not sure which was the culprit but really suspect the cap, and as the car is 7 years old I would consider the thermostat change as preventative maintanance. A couple of points to note: I had already purchased an aftermarket radiator cap from Autobarn (will be returning it) for $16 before I found out Holden was open. The genuine cap, which is slighly different, was only $14 retail. Secondly if you are buying a new thermostat be aware that it will come with a new housing. This is the same at Repco.
All is good with the world again...............................................................................for now.
Cheers, Stu.
 

RiCeY

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Wont do any harm replacing the thermostat, as you said preventative maintenance.

Glad it worked out for you.
 

Munz

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definitely radiator cap it done the exact same as you described in my car. hope all is well now
 

BehaveSS

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Glad to find this post, it's happening to me right now, camping at Uluru at the moment. Long hot drives to and from sites! First over heat occurrence was just right after I over took a triple road train, temp shot up to RED and engine light and safety mode engaged! I stopped and waited 30 min and started with the temp shooting right up even in idle with no ac running. The day temp is probably 30C on the Stuart Hwy. have used 10L of new coolant so far, each time I stop after a long drive I have to top up. No where to buy a radiator cap on any of the service stations on the way here to yulara! I suspected it is the rad cap, I will roll into the only yulara mechanic tomorrow before my long trip back to Sydney! Hope it is just a faulty cap. Oh in case you were wondering how I can still drive after the safety mode has been actived, I read the fault code with dashcommad and it was only the high coolant temp that was in alarm, I could clear it after the car was cooled and refilled rad with what clean drinking water I had to get me to the nearest station, which was 130km away at the time!
 
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