89 vs 91 Octane gas in offroad trucks? | 4WDTalk - Overlanding and offroad Forum
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89 vs 91 Octane gas in offroad trucks?

Pro Drywall

Pro Drywall

Well-known member
Any gas nerds here? Does it make a difference to run 89 vs 91 octane gas while driving offroad where MPGs aren't that important?
 
Depends on the year and the motor build. My Cruiser (1996) is a bit higher compression then stock. On long drives, the difference between 89-91 is enough to off set the cost difference. About four gallon usage difference in 250 miles. On my Tacoma (2019) I haven't noticed any difference.

On a modern high compression engine, the computer will compensate engine timing to make up for the lesser fuel. This will have adverse effects on engine performance. On a modern "normal" compression engine, the computer will still compensate but the difference may not be noticeable.

Bottom line is, test it. It will either make a difference or not.
If your lucky enough to find fuel without alcohol, buy that. Regardless what your told, our engines were not designed for any alcohol in the fuel. Not only do they run better without it, they also run cleaner without it.
 
Your question got me thinking and I went digging on YouTube and found this very interesting video:
 
That first video took alot of work but he left out a ton of info. He did show the alcohol test, so points for that. He also did mention octane and detonation.
The second video shows short tests on one vehicle and engine type. I should note that the "MPG" gauge on your vehicle is not designed with any accuracy in mind. Its more of a toy. I would get constant complaints about it in the shop. All of the factory manual's I've read state it was never designed to be accurate and you should not try to "repair" it or calibrate it.

Here's a little about modern fuel history. Note when I use the word "government"

1. Late 60's the government started being concerned with pollution from cars. Government funded testing shows possible improvements if the car is able to control certain parts like timing, egr, heating fuel, adding cats.
2. The government mandated emission controls. This is based on the government funded research. This would go into effect somewhere in the mid-late 70's
3. The auto manufactures didn't have the technology required to do this. They had to make it up as they went along.
4. An independent study (non government) found that by adding a small amount of alcohol to the fuel lowered emissions greatly. This was early 70's. The government didn't acknowledge the research.
5. The 80's. more government mandates. Car manufactures are still struggling to design proper controls.
6. Every few years the independent group's (non government) tries to put in their research regarding alcohol. Each time it's thrown out.
7. Mid to late 80's the manufactures start playing with fuel injection. The systems are better but still not there.
8. Late 80's. Government research shows fuel injection is best. Manufactures are given new mandates. Again they lack the technology to do this.
9. Early to mid 90's. Government research shows alcohol reduces emissions in "CARBORATED" vehicles. Fuel injected is mandated. Fuel milage standards are also mandated.
10. Independent research shows alcohol lessens fuel milage and attack's any aluminum as well as soft metal. It also showed alcohol can increase emissions in a fuel injected vehicle. The government threw that data out.
11. 1996. OBD2 is mandated as well as all vehicles will have fuel injection. This is a rolling smog check. Its designed so a smog station can just plug in and check all the smog devices. California requires Dyno testing instead.
12. Late 90's. Alcohol is mandated by the government in certain states. Independent (non government) shows modern cars don't benefit from this and its starting to destroy fuel systems. Alcohol is now being used to raise octane ratings.
13. Late 90's (depending on manufacture) fuel systems are being redesigned. Manufacture fuel milage and emission testing is done on fuel without alcohol.
14. Today. Modern cars pollute very little. Alcohol not only still increases emissions but it takes more alcohol to produce the same power as gas (about 3-1). This causes fuel milage to suffer.
15. Modern fuel is now breaking down when it sits. The additives as well as alcohol form acids quickly. This is seen in vehicles that sit for long periods of time. IE: ATV's, motorcycles, wet bikes. In my case, my tow rig. The acid not only is eating parts of the fuel system but ends up about as flammable as water.

Todays cars run better on fuel without alcohol. The data the government produces about alcohol improving anything is based on carbureted and very primitive fuel injection vehicles. In other words, outdated info.

How will your vehicle run on premium fuel? There are so many variables involved you need to do your own testing. Not just the alcohol but diffrent additives can effect your vehicle. Its not just station to station but state to state. Modern stations will use alcohol to raise octane. I see higher percentages of alcohol with some stations and less with others. Almost across the board, cheap fuel has more alcohol and expensive may not have less.

In the early 80's I met people doing independent testing. Most of this was finding ways to improve engines with the hope someone would buy the technology. I've also been around alcohol in racing. Today, I try to keep up with modern technology. Its always been difficult to filter out literal propaganda and partial truths put out by the car manufactures and the government.

Bottom line. Do your own testing on your vehicle. Read alcohol percentages and burn whatever runs best. FYI, some of the cheap fuel stations no longer show alcohol percentages. This makes me believe their skewing the octane numbers with more alcohol. I do know, they have to show octane, I don't know if they have to show alcohol.
 
No clue, I run the highest octane fuel available as I believe it burns cleaner and because of that, better MPG and power from my truck
 
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