[TrucksNCoffee]

My pickup is a '97 Chevy 4x4 with a 350 cubic inch/5.7 liter V8 TBI. The manual calls for 86 octane gasoline, so I put 87 in it at the pumps. I average 13.1 mpg around town, and 15.3 combined city/highway.

My son has a 2015 Ford F-150 with a 3.5 liter EcoBoost engine. He told me that switching from midgrade to premium gave him more an increase of more than 3 mpg.

Now, I assume that's because his newer pickup is "smarter" than my older pickup, but need to ask our knowledgeable members: Might I see an increase in mpg if I put the premium stuff in my tank? (I know, I could try it for the next two or three fill ups and see, but it's cheaper to ask first.)

 

[kschilk]

Theoretically, higher octane should result in lower mpg numbers. Higher octane means the fuel is actually less flammable to resist early detonation under compression, the reason it's only usually recommended in high compression engines. Hi-oc needs a hotter spark which due to the higher electric draw, puts more of a load on the engine causing it to burn more fuel...kinda' like running the a/c. Back when we could still get leaded gas, most motorcycle racers ran a mix of leaded and unleaded gas which yields a much higher octane level than anything you can buy at the pump. A small dose of leaded added to unleaded raises the octane considerably at first but after that, richening the mixture produces only small incremental gains up to a 50/50 mix. Beyond that, it no longer boosts the octane at all.

 

[darbo]

I have no scientific knowledge on the subject but pretty much agree with Kschilk. The rule of thumb that I always went with is run the lowest octane you can without any sort of engine ping/knock, especially under adverse conditions, hot weather, towing. I believe this practice should yield the cleanest burn and best mileage.

Caveat: when it comes to these new fangled turbo charged, computer controlled engines I have no idea!

 

[kschilk]

I have no scientific knowledge on the subject but pretty much agree with Kschilk. The rule of thumb that I always went with is run the lowest octane you can without any sort of engine ping/knock, especially under adverse conditions, hot weather, towing. I believe this practice should yield the cleanest burn and best mileage.

Caveat: when it comes to these new fangled turbo charged, computer controlled engines I have no idea!

Far fewer late model cars are recommended for premium gas than cars made in the '70s and '80s. Higher compression makes more power, lower compression uses less fuel. Naturally, everyone is going for mileage now so most newer engines are substantially lower compression. Oddly though, newer engine designs run super hot, comparatively which you'd think would just cry out for high octane to combat pinging but it's rarely recommended. Temp gauges on older engines generally hovered around 180 F while newer cars have been running at 210 F, minimum. It should also be noted that the temp gage in modern vehicles is lyin' its ___ off, it's not even close. Although thermostats are now generally in the 185-195 F range and the gauge rides at or around 210 F, most vehicles' cooling fans don't come on until the engine coolant temp is between 235-247 F.

 

[Car_Doc]

I split my gas 50/50 91/87 octane a couple of times.. According to the monitor on my drivers information center I get 2 more miles per gallon.
According to my calculations...I get.the same.
Granted... I have 7 inches of lift and 35 inch tires.i dont expect good gas.mileage. I'm just looking for what works best mileage wise.
Realistically , it costs.more to fill up.50/50 , and the mileage increase isn't there.
Just my .02

 

[GhostHorse]

The difference between his and yours is the turbo. For your NA engine, higher octane would be completely wasted.

I did a 3-4 month study once on this, tracking octane, brand, average speed, and average fuel economy. This was in a BMW engine, non-turbo, which was specified for high octane. At northern NM altitudes, non turbo, you absolutely do not need high octane in those engines. Heck, even my sportbike with 12:1 compression is happy with regular at these altitudes.

My study showed zero correlation between octane and fuel efficiency. Zero correlation between brand and fuel efficiency. The only like was (surprise, surprise) higher average speed means higher efficiency. In other words, highway mileage is better than around town. Who knew?

For your truck (and I have to reiterate what a GREAT deal you got on that truck!), I would never put anything but regular in it. That's what big NA American trucks are made to run, and you'll see no improvement in efficiency or engine cleanliness running anything else.

Just one man's opinion, but I've got a fair bit of experience and data to back it up.

 

[brojohn]

The biggest difference will be seen between blended(ethanol) gas and pure gas instead of octane number.
Here where I live (coastal Alabama) most all regular gas 87, oct has up to 10% ethanol blended in. Mid grade gas, 89 oct is usually offered without any ethanol at a higher price. Some stations offer mid grade both blended and pure at different prices. There should be a noticeable increase in the mileage on the pure gasoline.

 

[Ickthus]

Octane? Run what your engine calls for. Now what cuts into my mileage and performance is % of ethanol. I get much better mileage with ethanol free gas. I get 5 mph faster on my 1981 Honda C70 passport with ethanol free.

 

[bobbojama]

The newer F150 requires higher octane to run at peak efficiency, the lower octane causes knock and the knock sensor retards the timing to eliminate pre-ignition lowering efficiency, hence mileage. The older motors are stupid compared to the new ones. The only way to benefit from increasing the octane in the older motor is to mess with the timing, advancing it until you get a knock under load, and then backing it off until the knock goes away. Very little to be gained.....

 

[cassrh]

I read a article on that very subject, and they found no increased mpg by using a higher octane gas. I use what is recommended, but on 4 cycle mower engines, I do use a higher octane. For the 2 cycle engines, I use pre mix. The person that thought up ethanol should be shot.

 

[kschilk]

I read a article on that very subject, and they found no increased mpg by using a higher octane gas. I use what is recommended, but on 4 cycle mower engines, I do use a higher octane. For the 2 cycle engines, I use pre mix. The person that thought up ethanol should be shot.

Actually...:mellow:...I'd prefer drug, hung, drawn, quartered...:dry:...then shot.

 

[TrucksNCoffee]

Thanks to all for your answers. I understand now why my son's '15 Ford gets better mileage with the high octane stuff. Meantime, me an' my older '97 will stick with the recommended go-juice an' save some coin at the filling station.

PS to Ickthus - how much ya want for that lil' Honda? That there's a classy lookin' scoot! :thumbsup:

 

[garyh]

I just put in the recommend gas and let it go at that. The manufacture did all the research so why try to out guess them.

 

[GhostHorse]

Because they were making recommendations valid at every altitude, and I live in an unusually elevated area. And gasoline additives your engine doesn't need can cause buildup, in fuel injectors and on valves. I usually follow their oil recommendations, but I've had great results thinking for myself on octane. My Triumph Daytona sportbike's engine runs like net at ~65,000 miles.

 

[BC605]

Unless your engine has a compression ratio high enough to need the increased octane fuel, you won't see any measurable benefit from it.
Your son's Ecoboost is a turbocharged engine with a computer system that will increase turbo boost pressure (resulting in higher compression), when it has higher octane fuel that will retard premature detonation (a.k.a. "pinging") even with the higher final compression ratio. That additional turbo boost results in more power and higher efficiency, which translates to better mileage.

 

[rollin thunder]

I don't know if it helps or not, but I run two or three tanks a year of recreational fuel (good old 100% 91 octane gasoline)
My mileage drops about 2 or 3 MPG's, but afterwards, the engine seems more responsive. It could all be psychological, but I've been doing it since they came out with that "filler" called ethanol.

I remember when they stopped using leaded gas, my father would always dump some of that leaded additive into the tank. Thinking back, I'm glad we aren't spewing lead around any longer.

 

[grumpyoldcomputerguy]

I agree with most of the responses so far. I hope to add a little to the information.
I don't consider myself an expert but I do know some stuff about engines and fuel. First, lower grade fuel i.e. diesel and lower (like fuel oils); have more BTUs (read heat and energy) per pound of fuel than higher grade fuel, like kerosene, jet fuel, and gasoline. Octane ratings are a combination of factors, if I remember correctly, and have been used for several decades now. Modern engines will run on 87-93 octane fuels. But, like stated previously; sophisticated computer controlled engines with multiple knock sensors, high compression, and turbos, run best on the recommended fuel. If you run more than 2 points higher on octane you are probably just wasting your money. IMO.

Finally, I remember when we had to overhaul engines at 75000 miles. Now they run 200K regularly with just maintenance and regular trips to the shop for component diagnosis via computer. I know of one VW Jetta diesel wagon with over 750K miles on the original engine. My sister-in-law toyota pickup has over 400K on the original engine and tranny and runs like a top. "They don't make them like they used to" may be a good thing. It seems I rambled a it there.

 

[kschilk]

I agree with most of the responses so far. I hope to add a little to the information.
I don't consider myself an expert but I do know some stuff about engines and fuel. First, lower grade fuel i.e. diesel and lower (like fuel oils); have more BTUs (read heat and energy) per pound of fuel than higher grade fuel, like kerosene, jet fuel, and gasoline. Octane ratings are a combination of factors, if I remember correctly, and have been used for several decades now. Modern engines will run on 87-93 octane fuels. But, like stated previously; sophisticated computer controlled engines with multiple knock sensors, high compression, and turbos, run best on the recommended fuel. If you run more than 2 points higher on octane you are probably just wasting your money. IMO.

Finally, I remember when we had to overhaul engines at 75000 miles. Now they run 200K regularly with just maintenance and regular trips to the shop for component diagnosis via computer. I know of one VW Jetta diesel wagon with over 750K miles on the original engine. My sister-in-law toyota pickup has over 400K on the original engine and tranny and runs like a top. "They don't make them like they used to" may be a good thing. It seems I rambled a it there.

Folks used to rebuild the older engines mostly due to the recommended maintenance schedules but they'd run fine over 100,000. You could run 'em 'til they blew, then rebuild 'em multiple times if you wanted to. The key there, is that you could rebuild 'em and almost infinitely. It's true, some later engines make it to 200,000 or more but by 130-140,000, the computers working their butts off is all that's keeping 'em alive and there is no rebuilding them. Even though they still may be "running", they aren't performing near as they should. Newer engines are all throw-aways, there's not enough metal there to oversize anything and what little there is, is so stressed that it's already been living on borrowed time for a good while. Besides that, parts are so expensive on the new stuff that even a spark plug replacement becomes a toss-up as to whether it's more cost effective than just tossing in a new engine, since the difference in price comes to about a nickel. Later engines are designed to literally self-destruct due to their "interference" design. There is no replacing of broken timing chains or belts anymore, that once minor malfunction will now take out the engine. It's futile to try comparing engines in an old vs new context, they're two totally different machines. One was built to last for decades while the other, for just a few years. Fifty years from now, there won't be 2000 anythings at vintage car shows but there'll still be an abundance of pre-1980 cars drivin' to 'em.

 

[GhostHorse]

Fifty years from now, there won't be 2000 anythings at vintage car shows but there'll still be an abundance of pre-1980 cars drivin' to 'em.

Okay, I was going to stick to my usual taciturn silence until I read this last line. The record must be set straight.

Fifty years from now, cars from the 80s will all be permanently parked in sleep centers, helping insomniacs discover the joys that only a boredom-induced coma can bring. With two exceptions; the SHO stick shift Taurus, and the Buick Grand National. All other 80s cars deserve the fate they've mostly already received. For heaven's sake, that decade gave us the Plymouth Reliant K! If they did last forever, it would just mean the four horsemen have decided to add a fifth, and automotive blandness barely beat out people who talk on speakerphones in restaurants to be the fifth harbinger of the apocalypse.

Or maybe you meant the 70s, when 6 liters of fire-breathing Detroit iron made about the same horsepower as my 955cc Triumph Daytona. Yeah, it's easy to last forever when an engine so big it needs Gothic flying buttresses to support it can barely wheeze out more equine grunt than a 2005 Focus. Reeeeal excited about making those last forever. And then there's handling in 70s and 80s cars, which I can't discuss because moderators of all people should set the no-profanity example in this forum.

So, can the newer cars last? This article mentions a guy with a mid-2000s Mustang GT that had a quarter million miles with nothing but routine maintenance. And that's no 70s routine maintenance, with belts and plugs and oil and filter differential rebuild and carburetor rejetting and horsepower inhibitor reinhibition every time you get to the end of your driveway, that's 2000s routine maintenance. Oil change. Air filter. Plugs every third presidential election. Oh, and tires, because these cars actually have to deal with horsepower getting applied to pavement. Looking around the Mustang forums from that era, no one gets impressed until you're way into the 2x0,000 range. Even 2014-2017 Expeditions have a reputation discussed in multiples of 100,000. And you just know those will fill up the car shows.

Won't be at the vintage car shows indeed. Harrumph.

 

[Jake3501]

I would invest my extra sheckles into non eythonal gas as opposed to higher octane.