Keith-Audi-Turbo

My car has over 250k and I've mostly used 89 octane; however, many times I would fill up using 91 or 93. During a recent roadtrip, my engine block
over-heated and "blew up". My mechanic, (who I trust), said that he believed that the cause was due to using a lower octane gas. He mentioned that the age of the engine & mileage required that I use a higher octane...

Have any of you heard of an engine "blowing-up" due to usage of 89 octane...???

Just curious...

5000Q86

Yeah that can happen. the octane rating is a measure of how volatile the fuel is, or in other words, how fast it burns. low octane fuel (89) burns very fast and is more of an unstable burn then high octane (93) fuel. a fast burning fuel creates a sudden burst of force on the pistons and connecting rods during the power stroke, where a slow burning fuel will create nice even pressure throughout. that sudden force can wear out main bearings, piston rings, and in some cases, create misfires or backfires bad enough to punch a hole in a piston. some non turbo cars require a high octane fuel too, simply because that what it was designed to run on, but you should ALWAYS follow the manufacturers recommendation for fuel. generally, its ok to use a higher then recommended octane fuel, but never ok to go below it. hope that helped!

Pushbutton_auto

Never heard of Audi 5 pot blowing up ever ...


but yeah always use 98 down under, ours are 91, 95, 98.

Keith-Audi-Turbo

Yep, your reply was very helpful. Thanks again for chiming-in...

MarkPan

They've got a knock sensor... it'll run fine on 87, just slightly less power than with 89/91.

Keith-Audi-Turbo

Hey Gang, it appears that the cause of my problem was a busted radiator hose, which in turn caused the engine to over heat. I was on the highway doing about 75, when trying to make a pass then -- BOOM...!!!

Needless to say I'm hoping for a very uneventful fall & winter driving season...

Thanks to everyone for your input...

GroupBquattro

I would not mess with anything less than premium, especially if the car is even slightly modified (ecu) Back in the 90s, while I was rallying my 5000tq, I added gas between stages and the knock light came on under slight acceleration. Ned Ritchie- Intended Acceleration who tuned my car and was "in my corner" did not allow me back in the race till we added a gallon of toluene to increase octane. He told me that once the knock light comes on, it could be a matter of seconds before the engine goes. And I only had stage II and wastegate mods at the time. After this episode, I always added toluene to the gas before a rally. I got it to 2.0 bar and it ran soooo sweet. Back in the day, a $10 gallon of toluene seemed expensive since gas was 1.50, now at 4.5 the difference is not that much.
Bottom line, racing or not, I would go with premium gas, car loves it.