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VY rattles (and breaks down) when running on unleaded, but not on LPG


New Member
Feb 11, 2017
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South Australia
Members Ride
Hey all,

First post here. Not car savvy but I've driven Commodores my entire life. This is my third car, and the first time I've run into issues.

I bought it for $800 and it runs on petrol and gas. When I first bought the car, it was overheating. I didn't realise at the time, so I took it for quite a long drive and got stranded out in nowhere. The car just died. My mate came out to jump start me, and managed to get me going until we got to a service station. Because of the battery issues, he said it was the alternator not charging it enough to start. But upon putting a multimeter on it, the battery and alternator were both fine. He said that the car wouldn't have been starting because it would have been overheating and the metal would've expanded as he put coolant in and it started pissing out of the water pump as fast as you'd put it in.

So I'd had a new radiator, water pump, and pipe installed two nights ago. No more leaks.

I went for another considerably long drive yesterday and made it most of the way, even though I did appear to be running pretty hot. (I wasn't entirely sure, as the temp kept jumping between MAX and just under half way, or in between)
I made it all the way and back, but switched over to petrol when I got back into town, and that's when the engine started rattling. It sounded like five things were loose, but only when it ran on unleaded, switching back to gas resolved the issue.

This obviously became a problem when I ran out of gas half way between my house and a service station. There appeared to be a "sweet spot" with the accelerator on petrol, where putting it in half way would cause the engine to rattle, but lifting it off or putting it all the way in would make it run okay. Accelerating "normally" would cause it to rattle so much that the car would just die at the next set of lights. I was stuck at an intersection with my hazards on waiting fifteen minutes for the car to finally (presumably cool down enough so it would) start so I could make the final stretch home.

I'm 90% sure this is to do with the LPG and petrol but I've never heard of such an issue. Running on LPG still seems to make it pretty hot but the coolant is flowing through now with a perfectly new radiator.

F l a k

Feb 25, 2010
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Wagga Wagga, NSW
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'94 VR Exec
Doesn't sound good. Take the car and the history to a radiator/cooling shop and see what they think. You could have cooked the motor, maybe partially seized the thing, and blown a head gasket/s. Best to get a definite diagnosis before you do anything much else. Won't cost too much for them to have a look, maybe $100 or so.

Have you checked or replaced the thermostat? Is it pushing coolant out? Water in the oil?


Well-Known Member
Jun 9, 2011
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Members Ride
VZ Wagon
You may have gas and fuel running to the engine at the same time due to faulty switch/valve.
If possible, idle the car on gas and turn off the gas supply valve at the gas tank, and the car should stall after a short period.
Then see if it will start and run on fuel.
If so, then you need to get the car to a gas specialist to correct the problem valve/switch.

As to the overheating problem, you may have an air lock in the cooling system.
The gauge should not bounce around max to midway.