Fuel 101- What You Need to Know Before Your Next Fill-Up

christieDid Christie fill up with Top Tier Gasoline?

Updated 8/6/15

I recently had the opportunity to interview a fuel efficiency expert deep inside the automobile industry (Rich). I learned more about fuel in that 20 minutes than I learned the 25 years prior.

I know that fuel efficiency is a departure from my previous blog topics. So far I’ve talked about mental illness, Disney, Jared from Subway (who by the way paid $100 to have sex with a 16-year old per TMZ), emotional abuse and signs of middle-age. When researching how to blog, I often read about the importance of finding your voice and sticking to it. I guess my voice is complete randomness mixed in with a little Disney.

Fuel 101- The course you never had in school

1) Not all gas is equal

When you fill-up at Speedway versus Costco it’s not the same gas; even if you use the same octane. Why? The amount of detergent at Speedway is at least 3X less. Detergent helps clean and prevent engine and fuel injector build-up, which in turn improves your car’s fuel efficiency, drivability, and performance. Whenever you run your engine, soot develops. When soot remains, your car performs similar to a clogged shower head. It will still run, but your experience is not as good.


You are able to locate Top Tier gas stations quite easily, using the site above. Rich suggests you primarily fill-up at these stations. An occasional stop at Speedway is okay but you should make an effort to minimize the frequency of your visits. Octane and detergent levels are unrelated, so even when buying premium gas, you aren’t guaranteed Top Tier quality.

2) Most cars run fine on 87 octane

Your owner’s manual is a great source of information. It will inform you if higher octane gas is required or recommended. Chances are you will find regular octane is just fine. If not, it is likely you are driving a premium car (hey playa, hows the BMW) and high-performance vehicles (turbo/super-charger). Cars in this class will experience up to a 10% difference in horsepower when using premium. If your manual says higher octane is recommended (versus required) you won’t experience as much improvement and it’s purely an optional expenditure.

When you buy 89 octane it is normally priced in the middle of 87 and 93, although you aren’t really getting the mid-point between the 2 octanes (which would be 90) According to Rich, there isn’t any reason why you should purchase this octane; unless your owner’s guide says to or you are trying to impress a girl.

You will see 85 octane, which is not the same as E85, in higher altitude markets. You will notice however, that your car manual states you should use 87 octane or higher. This recommendation still applies if you are in the mountains; therefore, even though this gas is offered most auto manufacturers does not recommend using it. Why? There is potential for your engine to be damaged and your car’s power to degrade. If you’d like to hear it from a source besides Rich, check out this article:


Octane refers to how quickly your fuel ignites, which is called it’s flash point. When this flash point is too low, pre-ignition occurs, adding stress to your motor. This is when you experience “engine knocking”.

3)E85 is only good if you are about to turn in your rental car

E85 means that your gas is 51-83% ethanol (made from corn and/or sugar). E85 is also known as flex fuel  and was created to end our dependence on oil from the middle-east.  You will see this type of gas in the mid-west, where farming is more prevalent. What most people don’t realize is that you get 15-30% less fuel economy than normal gas. If you are a farmer and can purchase E85 at below market rate great, go for it. Otherwise, the cents you’ll save per gallon are really not worth it.  Not only is your fuel efficiency impacted, but Rich warns you may damage your fuel system with continued use. If your car can tolerate E85, it will say “flex fuel capable” on the fuel cap or in the owner’s manual.

Note: Even regular fuel has up to 10% ethanol; however, E85 has more of it. DO NOT USE E85 UNLESS YOUR CAR MANUAL STATES IT IS FLEX FUEL CAPABLE. Doing so will likely damage your fuel system.

Edmunds.com recently completed a test comparing regular gasoline to E85. You can read more here: http://www.edmunds.com/fuel-economy/e85-vs-gasoline-comparison-test.html

4)It’s not that hard to improve fuel economyYour driving behavior can increase or decrease your fuel economy by up to 20%. Here are Rich’s tips for getting more for your money:

  • Properly inflate your tires per the instructions located in your driver’s side door jam. The pressure listed is based on cool tires, as you drive tire pressure rises.
  • Get the junk out of your trunk. In my case, it brings the boys to the yard but in yours, it may cost 1/2 mile per gallon. This 1/2 mile loss occurs with every 100 pounds added. Therefore, you finally have an excuse as to why your mother in-law needs to find her own ride!
  • Combine trips. Your car is most efficient when the engine is warmed up. The first 5 minutes of your drive will get about 1/2 the fuel economy.
  • Coast to a stop versus using your brakes. When you aggressively drive to a red light and brake, energy and momentum is absorbed. The less of this you can do, the better.
  • Slow down. Above 60 MPH your fuel economy drops rapidly, due to increasing wind resistance. Wind resistance is 23% less at 70 MPH than 80. In case you are wondering Rich did the math, not me. So, it’s right.
  • Make sure your car is in good working order. Flat/low tires and a poorly tuned up car can throw off your fuel economy more than anything else. Even more than buying that gas made of corn!
  • Your AC running doesn’t have as much impact as you may think. The federal fuel economy test is run without AC, but for the average car this would only lower your fuel economy about 1 MPG. However, certain cars like hybrids can be impacted by up to 5 MPG. Keep in mind too, if you are going over 40 MPH with your windows down, this is worse than having the AC on.

What about those chain e-mails with fuel saving tips?

Contrary to urban legend, filling up just after the tanker visited isn’t the end of the world. Yes, the process of filling up the tanks may stir up sediment, but there are filters on the pumps which should prevent most of it from getting into the fuel. Similarly, filling up the coldest part of the day isn’t as important as you may have read. The tanks are about buried several feet underground. Similar to a cave, the temperature doesn’t change much. Legend also has it you should fill-up your car when it’s still 1/2 full. Only particularly old cars  – those before Evaporative Emission Standards -will benefit. Emissions filters in your fuel tank will prevent condensation in your tank.

Does Rich have any other tips?

  • If you have a car that you store 1 month + without driving, it’s a good idea to buy a fuel stabilizer such as STA-BIL. This same product can be used in your snow blower or lawn mower. It’s easily available online or at auto-parts stores. You simply put it in your tank at your last fill-up. By doing so, your fuel will stay at the same quality and sludge deposits will be prevented.

At this point, you should know more about fuel than you ever thought possible! Look for more tips from Rich in the coming weeks.

A note from Northville Mom: Our fuel expert, Rich, had no idea what I meant when I said my milkshake brings the boys to the yard. If you don’t either, there’s a video you need to see: