I'm currently in a money crunch and wondered if it was OK to use mid-grade fuel instead of premium. Will there be any mechanical problems not using premium? Besides the highest grade of fuel we have is 91 and mid-grade ranges from 88-89.

 

How much more is premium? Normally 10 cents or so. Is it worth the dollar or two to find out.

 

At lower octane your ECU will adjust and pull timing, but it has to sense the inevitable knock first. If you go into VTEC, it will knock some more until the ECU retards timing enough to accommodate your fuel choice. It's up to you to decide if this is OK or counts as a mechanical problem.

You get worse economy and performance so in terms of total $ spent it will be a wash. But how much is your time and enjoyment worth?

 

The car will run fine on midgrade.

It is no longer a 10 cent difference between grades. I think there is usually about a 20 - 40c difference (in IL, US anyway) between midgrade and premium. So, you're saving about $2 - 4 per 10 gallon fillup.

Do your own math.

Assuming a per gallon price of $2.60 vs $3, midgrade would be about 15% less expensive. So as long as your MPG doesn't drop by 15 or more percent, you're not losing money on the degraded MPG from running a lower octane than the ECU can take advantage of.

 

You should, however, listen for audible ping or knock. And you should really avoid bogging the engine. Adjust to a slightly higher shift RPM and lower throttle angle.

Really listen for it on hot days.

 

Yeah out in here California from mid grade to premium. It's about 10 cents. More when you get out in the boonies. I can go to 76 and get mid grade 2.76 or premium 2.86

 

Gasoline prices vary wildly by the day and location. Shop around for gas if you can. For example here in Cleveland today:

Regular (87) $1.99 to $2.29
Mid Range (89) $2.33 to $2.89
Premium (93) $2.53 to $3.10

Note the price overlap with 89 and 93. At some stations Shell 93 is cheaper than 89 at some other stations. My car was tuned on Shell 93 so I prefer to run it on this gas.

If you're like me you don't start thinking about gas until the gauge is near the bottom or the little fuel light comes on and then there's no time to shop. Shell 93 convenient to me is running $2.89 and 89 is $2.45. A Happy Meal difference in a fill up.

Someone may want to check my math but the 5000 miles I drive my S2000 annually at 25 miles per gallon is 200 gallons and the 44¢/gallon price difference only comes to $88. Double that if you drive 10,000 miles.

-- Chuck

 

^That's also with the generous assumption that your MPG will remain constant at 25 with the lower octane. It won't.

 

Idk if it will reduce the MPG by 15% or more. Maybe a 10% loss in "city" or 5% in "suburb" type driving. Probably no effect on the highway.

 

There have been times on our drives that 91 wasn't available or the clerk was honest enough to tell me that they haven't had a delivery of 91 in months, so I went with 87. Have done this 4 or 5 times out in the sticks where you were 100 miles+ from the next town, I didn't lose any gas mileage but I didn't take it to redline either. We drive the western US and Canada. We also got 2 gal.(87) free one time from a US Park Ranger when I could not make it to the next town on what I had left in the tank.

Out west you can go 100's of miles without seeing a gas station out on the back roads. And when you come into a town that only has one gas station you should ask how long the 91 has been sitting in the ground, I'll take younger 87 over older 91.

ROD