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So I decided to do an experiment with my 1996 chevy k1500 with 3.42 gears using my scan gauge. I usually put the cheapest gas I can find in it which is usually 85octane from a gas station that I have heard multiple reports of ice chunks forming in the gas they got from there. Dumb I know but it gets me around. Today I felt richer and decided to put chevron 87 octane in and in the short 15 miles a drove I seemed to be averaging about 1.5 mpg increase over what I usually get, and got about 22mpg! Going 30-45mph. I drive this pretty often especially lately and I don’t think 15 miles can bring any conclusion so ill pay more attention,to the numbers, drive some more, and post what I find.
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Higher octane gas has lower energy capacity – that’s why higher octane gas does not detonate early in the engine (knock). However if the engine is knocking, the ECU will retard timing and you will lose power. So you want the octane to be as low as your engine will handle without knocking for the best MPG.
My engine requires 91 octane (as per manufacturer), but when I put 89 in it when weather is cool or cold, I do get a little better MPG and of course a little more power on the highway. Not sure if the engine knocks a little in city driving on 89, but I haven’t tried it as knocking is bad for your valves.
Well I have driven the same 15 miles probably 20 times over the last week and I’m still getting around 2mpg better than I was. Sometimes averaging 22mpg! But usually 20mpg going and about 18-19 mpg coming back. Plus the engine seems to sound healthier And have a better gas pedal. But that could be my imagination.
I was taught in automotive fundamentals that one would get zero benefit from using a higher octane than what the manufacturer requires. I was watching your post carefully to see if your actual data corresponded with what is being taught in our auto program. There are still a lot of variables to consider though: temperature, relative humidity, altitude, ECU drive cycle, computer commanded maintenance & testing, computer driven timing, driver attitude & style of driving, varying routes, uphill and downhill grades, varying changes in vehicle gross weight… the list goes on.
Well I have driven the same 15 miles probably 20 times over the last week and I’m still getting around 2mpg better than I was.
Have you deviated from this route at all? (even once?)
The engine could be pinging. Could explain why you are getting better mileage on higher octane. When it pings, it makes less power and more heat.
This is true. And no I go straight there and straight back, (going there doing whatever we have planned then just me on my way home is when I have been watching my mileage) When I drive that route. It’s to my girlfriends so my attitude is generally pretty good lol. But I can definatlyy see how my attitude effects my driving along with all ther other variables. But also over all around other places it seems to be getting better mileage all around too, but I can’t say that for sure because I don’t drive those routes as often.
My coolant temp usually runs at 188F almost all the time once in a while it will drop Down to 186 or up to 192. I think it’s a 195F thermostat and the radiator is new. I’m debating putting a new thermostat in because I don’t know when it was done last and it couldn’t hurt anything.
I beleive my manual calls for no less than 87. I also know that my dirtbike doesn’t like any 85 octane and I get alot of engine noise with 85 in it so I put premium in it I forget what octane it is though.
Here in the UK, I’ve found on many occasions even though RON95 is specified, most of the major petrol companies use there best fuel Ron 98 or 99 and put an additive package or an improved additive package over there regular fuel in there higher octane fuels.
Most of the MPG gains on such fuel can probably be traced to better control or removal of deposits in the combustion chamber from these fuels. It’s defiantly there and My car definitely tends to run smoother with better MPG on both cheeper and higher octane fuels once it’s had a tank or 2 of say Shell V-power ( Nitro) through it.
Higher octane gasoline is less resistant to being ignited by the high temperatures caused by the compression process in the combustion chamber. Most high compression engines require 91+ octane gasoline but some high compression engines can adapt to the lower octane by communicating with the knock sensors/O2 sensors and will retard engine timing to eliminate the premature detonation.
As an experiment I decided to put 91 octane in my vehicle as opposed to 87 to see if it would give any more power or mileage. I got about an extra 20 miles out of the tank but the 91 I used contains no ethanol. I then put 93 in and I’m getting worse mileage than 87. The engine does seem to have a little more pep at higher rpm’s for some reason.
The first tank was cheap gas (91 octane) from a grocery store chain called Martin’s. The second tank was Shell V Power 93.
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