Sometimes, things are intuitive – do one thing, expect a response, and that’s what you get. But there seem to be plenty of other times when intuition doesn’t quite match up with reality – and that’s where folks like me sometimes arrive and try to explain things. Once in a while, these little oddities can even add up to some pennies in your bank account – or, in this case, some dollars saved at the gas pump.
Many modern higher-performance engines are now equipped with ping sensors – if you run lower-octane gas, the engine pings, the sensors pick up on it, and change the engine’s mixture or timing to accommodate the slower-burning fuel. The turbo V6 in my Saab 9-3 is one such engine: the gas cap indicates the minimum octane is 87, but “for best performance” you should feed from the 93-octane buffet.
I’ve run 87-octane fuel just about every fillup since I bought the car nearly a year ago – and tolerated the occasional pinging and corresponding reining in of the engine. But for the last two fillups, I decided to bite the bullet and punch the 93 button. What I’ve found surprises me – even with my … um … spirited driving style, I’ve seen about a 2MPG increase in my fuel economy. I chalk this up to the engine producing more power to move the same amount of weight, thus increasing efficiency.
I decided to run some numbers, and figure out if filling up with pricier gas is actually saving me money – and meeting with moderate surprise on my part, it actually is! With gas prices where they are right now, burning 87-octane at 22MPG costs me about 17.9 cents per mile. But combining the change in fuel economy and the increased price of 93-octane gas, it only costs me 17.3 cents per mile when I fill up with the lesser-used side of the pump. While filling my 16.4 gallon tank costs me $3.44 more with 93-octane, the extra miles I get from that tank (in the form of improved fuel economny) would otherwise cost me $5.89 in 87-octane gas.
As a result, by filling up with 93 and driving the way I always do, I actually save $2.45 per fillup and go almost 33 miles further before feeding time comes around again. I imagine that driving for fuel mileage would increase the gap sizably, since short-shifting keeps the engine at low RPMs, where the 87-octane-induced pinging is most likely to occur.
Of course, nothing comes without caveats. If your engine doesn’t have a ping sensor and is tuned to run fine on 87-octane, then going to 93 isn’t going to save you a drop of gas – and thus isn’t going to save you a thin cent. But given how many vehicles are out there that do, I wonder how much gas we could save if we all switched to 93? In one year, I’m estimating I’ll use about 50 gallons less alone.