“Is it true the on board computer will adjust for the octane? My van recommends 91 but some stations only have 89 or 93, others have 91. I use 89 if 91 is not available, but recently heard it is bad to go from one to another. Is that true?”
The octane level required is based on the compression ratio of the engine. On board computers will make adjustments based on input from a knock sensor. Knock generally occurs when the octane level is too low for the compression ratio and the computer adjusts by adding more fuel. So if your engine is designed for 91 then you should run 91; 89 will work but you’ll probably get reduced mpg and negate any savings on the per gallon cost. If you bump up to 93 you’re just paying more for no benefit if the engine is designed for a lower level. However, if it were my car I would use 93 when 91 is not available, knock from low octane is hard on the valve train, in older cars (60’s) it was easier to hear the knock/ping when you got into the loud petal.
Interesting thanks. Do you know if your recommendation applies to a 2006 Buick Lucerne?
I’ve been told it’s designed for 93 octane but the computer will adjust for lower octane levels just as you said. But I didn’t hear about this savings being offset by higher fuel usage but what you say makes sense.
If I should go to the higher octane will I see an immediate rise in my fuel economy or will it take a while for the difference to become noticeable?
Thanks in advance for any help you can offer.
I thought about the octane issue. I have sprung for the Hi Test for the last couple of tanks, with no change in range. the 93 Octane doesn’t seem to make any difference.