Question about Chevrolet G30

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Is high-octane gas killing my older engine?

Recently purchased a 1984 Chevy Mallard RV (on a G-30 chassis, 5.7L V8, gas engine,). We started it multiple times without problem, only being told by the previous owner that it needed extra time to warm up in colder weather.

We drive away, hit the gas station since there seems to be only a splash left in the tank, and the idiot that is me hit the high-octane button instead of regular unleaded. I put 20 gallons in her and drove her home without consequence (5 mi. city drive, about 30 minutes at 30mph.)

Once parked in the driveway, we turned her on a few times over the next few days to reposition her or let our friends listen to the engine (which sounded fine at this point).

To the problem: Yesterday, we try to start her up. She starts begrudgingly and is idling roughly for about a minute. Tapped on the gas pedal when the engine started sputtering because it sounded like it was going to die. Tapping the pedal caused a bit of black smoke, then a plume of white smoke, to come out the exhaust pipe. Smelled like burning oil, then unburned fuel.

Then she died.

I figured I flooded the engine and pushed it too hard on a cold, cloudy day, so we left to let the engine settle. Came back an hour later, worse results. Turning the key shows there's plenty of battery power and a bit of oil pressure, but the engine will only rev 2 or 3 times before ceasing entirely.

It's much warmer and sunnier today, so I'm thinking about trying to start her one more time and let her run without touching anything for a good 15 minutes. But doing so raises the following concerns:

If it starts, will using the high-octane fuel totally ruin my engine, even if we aren't pushing her hard? Will I have to run the engine bone dry or have the fuel line/tank emptied and flushed /before/ I can again put regular unleaded in it? If so, do roadside assistance companies like AAA have the capacity to do fuel exchanges in volumes larger than 20 gallons?

I appreciate any answers and apologize for the rambling.

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  • Chevrolet Master
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The gas is not the problem. You have problems with the engine and related control system.

Posted on Feb 27, 2017

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Posted on Jan 02, 2017

jimbopickens
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SOURCE: ROUGH IDLE,WET SPARKPLUGS,KILLS

The Symptoms tell me it is a head gasket. A leaky or bad head gasket would cause all of the problems that you mentioned.

Burning water causes White Smoke, Burning Oil causes Black Smoke. The oil and water are mixing with the gas in the cylinders and causing it to run bad. Pull out the dipstick and look at the oil on it. Does it look like good oil? Or does it look watery and or foamy or grey colored. Open up the radiator and look inside, do you see oil?

This seems almost text book to me... I would have someone local to you to have a look at it to be sure.

Posted on Nov 23, 2008

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