Mixing Gas Octane

For some reason I have been putting 91 in my Tundra since day one. I have 3/4 tank of 91 now and want to top it off with 87- and continue to use 87. Any know issues with mixing octane? Some spots here are at $6/gal! I work on a Marine Corps base so I fill it up at the base service station.

 

No problem mixing octanes

 

If you beat on it (pushing high rpm or towing), i'd keep the premium. If you drive easy, go with 87.

I strictly fill up at costco, and premium is 30 cents more than regular...i'm dap tuned, so i'll pay the extra and get premium.

 

You can tow with 87, the engine isn't going to detonate with it.

 

Itll run a bit rougher on low octane, especially if it flex fuel. You can always get an octane booster and add it to the 87. That is what id do in the z28, a tank of 89 octane and a splash of octanium.

 

No problem. Around here mid octane is mixed at the pump. My flex fuel runs and tows fine on 87. I have experimented with higher octane fuels any increase in MPGs did not justify the higher price.

 

Many people have a misunderstanding of what higher octane fuels do. Your Tundra's modern computer controlled is designed to run on 87 octane and won't detonate with that octane. Older high compression vehicles are a different story entirely. Higher octane fuels do have more detergents in them and there is an advantage to that, but a bottle of fuel system cleaner a couple times a year will cost significantly less than buying premium fuel. Premium fuel does not increase mileage or performance and the lack of it won't make your Tundra run rough.

 

I tow and off road my truck hard and the next tank of premium would be it’s first.

 

by mixing 3/4*91 with 1/4*87, you will have 4/4*90 octane.

Sincerely,
Math

 

Years ago I did an analysis with my Accord. Shell 93 octane gave me about 1 mpg more, 32.5 up to 33.5...or an increase of about 3%, yet the 93 octane cost over 15% more. On a purely financial basis, 93 octane is a huge waste of money if your engine does not require it.

 

A full 38 gallon tank of 93 resulted in money lost. Otherwise, no difference at all. Same engine sound, same vibrations level, same MPG.

I saw a difference filling up 2.5 turbo Volvo with 87, it halved its max boost very quickly, compared to 93.

In a relatively low compression, natural aspiration 3UR-FE higher octane is not necessary. It may be necessary in other modern big V8s that have a higher compression ratio, or they will run retarded.

Also on cleaning additives once in a while: about a year ago I took apart a typically neglected engine with 220k on the clock. The car was running on regular most of its life. Fuel injectors were clean, with a good spraying pattern. Not sure extra additives are even needed these days.