Okay, so I was struck again by the cost of gasoline as I was filling up yesterday. Even more so, I was amazed by the fact that the Premium stuff costs about 20 cents more. Who buys this? And why? Does it do anything different? Does it release fewer pollutants? The only reason I can think of as to why it would be better is that it perhaps burns cleaner. So do you guys buy the premium? And a third question to add to the heap: why go for the middle one? It seems like a poor compromise.
High octane fuel is only needed for engines with a high compression to require it to prevent detonation - knocking in other words. For other engines it is a waste of money. The potential energy/pound of fuel is about the same for all gasolines and in any case, the octane rating indicates the anti-knock properties of the fuel and not the energy content.
My 97’ Honda Accord gets regular unleaded cause that’s what the manual said to put in it.
My 99’ BMW R1100S motorcycle gets premium cause that’s what the manual said to put in it.
As far as what i’ve heard, unless the manufacturer tells you to put the premium in, it’s just a waste of your money.
I will occasionally, if I have the money, put a tank of premium in my truck. Since it’s a 1971 pickup that was converted from leaded to unleaded when it was rebuilt, it really prefers high-octane stuff. It runs ok on 87, but I can notice a major difference when it has 92 in it (I can even pick up a minor improvement with mid-grade.)
Well, that explains the expensive stuff. But what about the middle brand? Do manuals ever specify that? People must buy it or it would have gone away a long time ago, but I don’t see how.
As people have already answered, premium gas is only really necessary for engines that require it to run well. However, there are a large number of mooks out there who figure “The number is bigger and it’s more expensive. It must be better!” I imagine the oil companies do little if anything to discourage this kind of thinking.
As other folks have said, I use premium because the manual say to; it prevents engine knock. However, when I was in school and I was broke, I switched to regular for a while to try to save some money. Turns out my mileage went down, making my total gas expenses equal whether I use regular or premium. So I went back to premium.
My '03 Dodge RAM truck specifies mid-grade for the 5.7L Hemi engine. According to the manual, you can use regular grade, but they recommend the mid-grade for better performance.
The higher octane is required for both high compression and forced induction engines. It allows greater timing advances. My Ford TurboCoupe runs both grades of gas because it as a fuel selector switch. It basically changes the ignition timing to account for premium or regular fuel.
Thanks for answering my question. So basically some engines require it; otherwise there’s no benefit to using anything above normal. And apparently some manuals even specify the mid-grade. I wonder if the high octane would be even better for the engine?
Funny, that’s exactly what the manual for my '96 BMW R1100RS motorcycle says. Works fine on 92 octane. Would probably knock, at least on a really hot day, on anything less.
Better in what way? Unless the engine is specifically designed for higher octane you will be throwing money away and may possibly damage your engine. Cars designed to run on mid-grade don’t need premium, there isn’t any more power in higher octane.
I used to own an 1988.5 (yep, that really was the “model year” Ford assigned it) Ford Escort. The owner’s manual called for regular, but I found that in its old age it tended to knock badly on that stuff. Mid-grade eliminated the knock, so I used that.
I didn’t really spend too much time or effort getting to the bottom of this, but I was given to understand that it was often caused by carbon buildup in the cylinders which effectively raised the compression ratio.
Whether this is really true I still don’t know. The car met a collision-based demise before the condition of the engine really became an issue.
Yes, carbon buildup can raise the compression ratio and cause knocking. However the engine needs to be close to the line anyway and probably should have been specified for a higher octance fuel to start with. The knocking can also dislodge carbon from the combustion chamber. In fact knock can even tear out metal, with aluminum heads being quite susceptible to being damaged by engine knock.
I drive an 86 Caprice, and always put the mid-grade (89, I think,) in it. On the rare occasion that I do not, I do notice a lot of engine knocking.