Colorado gas grades: A look at 85 vs. 87 vs. 91

[@jetsgardner5490]

Warning. Unless you're at a high altitude don't use 85 octane if you're planning a trip to lower altitudes. Some car companies will actually void you're warrantee if you're caught and won't cover the damage.

[@GlennC789]

That's fair. One of the few cases I might use a higher octane than 85. But where I live you can't really get below about 4,000ft without burning through a whole tank anyway. And in practice even with old primitive engines I never noticed much if any difference - if you hear knock, back off a bit/gear down, problem solved and you need to do the same even with higher octanes.

[@GlennC789]

Surprisingly good story. Most people seem to think higher octane means better fuel. That is wrong: octane measures only one thing: resistance to knock. If your engine doesn't need (or can't benefit from) higher resistance to knock, higher octane will not help you in the least, it's no better for your car whatsoever. And if it's a modern engine with a knock sensor and computerized engine controls, you might be getting 2-3% more peak power while spending almost 20% more, again with no other benefits at all. I haven't heard engine knock (or ping) for many years now, despite always using the lowest octane fuels, thanks to the aforementioned modern engines and their knock sensors. Yet I have saved many thousands of dollars and never noticed any lack of performance.

[@darkfur93]

Check your vehicle manual. Running 85 octane will void your warranty in most modern cars.

[@GlennC789]

Not at elevations where 85 octane is sold. Manufacturers can't void your warranty unless they can demonstrate a lack of care (maintenance, etc) led to the problem; and they also can't simply void your entire warranty for one reason: thay can't for example void a body rust warranty based on the fuel you use, since the two aren't related. If a car calls for 87 octane, and you live where I do and use 85, you're absolutely fine. Also anything still under warranty has a knock sensor and adapts instantly to any lower octane, which makes the entire question moot.

[@antiquehealbot6543]

​@@GlennC789word to word, F150's manual says 'using 85 octane gas may void your warranty'

[@GlennC789]

I'd like to see that taken up in court. Assuming you're right, "may" void your warranty would put the burden of proof on Ford. I had en Ecoboost Ford although not a truck, and I could not detect any difference at all between premium (91 here) and 85. That car was always pulling timing, I could tell it was very aggressively reacting to undetectable (by driver) levels of engine knock. It made it worse to drive but would be very hard to argue engine damage. I could see that IF the knock sensor went bad, and that as a result destructive engine knock happened, AND the owner neglected to fix it, Ford could have a case. @@antiquehealbot6543

[@aaronbode9622]

@@antiquehealbot6543the barometric pressure is lower at high elevation you don’t need more octane because pre-detonation is less of a problem here at high elevation, nope that’s not true I’m a auto tech and it won’t void your warranty, they are correct the knock sensor compensate’s for it, driven all over the Rockies and live in Colorado I’ve pumped up 85 and 86 octane gas in Wyoming and Montana not a single problem, once your west of Billings, Montana you don’t have 85 for regular unleaded anyways, it goes back to 87 for regular, So no it’s not true it’s a myth. It only matters with performance car’s that take mid grade 87 or 91 premium.

[@gunit6815]

87 is regular unleaded, 89 is mid grade and 91 is premium some stations have 94 as well here

[@MrGiggle72]

E88 (15% Alcohol) is a very good alternative to 85 Octane and between 5-15 cents cheaper for vehiecles 2001 and later.

[@jnvivian]

The advice that 85 at high altitude acts like 87 at sea level is only good for engines with carburetors, where the thinner air compensates for the lower octane. Engines with electronic fuel injection (which is pretty much all modern car engines) automatically compensate for the thinner air, so you really should run at least 87 and not 85 in modern engines designed for 87 octane. If you run 85 in an engine that is designed for 87 and has fuel injection, the engine will detect the knock and retard the timings to eliminate the knock, but that drastically reduces fuel efficiency and increases engine wear since the spark fires earlier to prevent knock, costing you more money in the long run. When the spark fires earlier, the engine has to fight the exploding gasoline and air mix for longer until the piston reaches the top, wasting energy from the explosion that could not be used to push the piston down.

[@GlennC789]

That is absolutely not true. At higher elevations air is thinner, resulting in lower combustion pressures, therefore requiring less octane. Carburetion vs fuel injection makes no difference to this at all.

[@bsanchez3563]

@@GlennC789 actually it does be ause you can manually adjust the carbuerators

[@GlennC789]

@@bsanchez3563 No - adjusting the carburetor only adjusts the fuel/air ratio, which fuel injection does automatically. It does not magically make the air thicker. There is still less air, less combustion pressure, and therefore less octane is needed.

[@SaraK_69]

​@GlennC789 you are absolutely wrong.

[@SaraK_69]

​@@GlennC789you seriously need to go to school kid.

[@Quin9296]

This low-octane gas doesn't apply to turbo engines.

[@tedwalker1370]

Most engines today have anti knock sensors, so you will not hear a ping. If you do hear the ping that sensor may not be working. What it is supposed to do is adjust timing so the low grade gasoline doesn't destroy your engine.

[@SnubBarracuda]

The thought that 85 acts like 87 at high altitude is based on an over 80 year old study on engines with low compression. It isn't true with modern engines. Plus like the other commenter said it voids your warranty the instant you do it because modern engineers know better and tell you what to use in your owner's manual.

[@igorrosales1799]

What would you call a modern engine/car? Starting from what year?

[@SnubBarracuda]

@@igorrosales1799 like 90s and later.

[@igorrosales1799]

@@SnubBarracuda damn, mine is 2008 and I filled up the tank with 85 octane

[@SnubBarracuda]

@@igorrosales1799 It will probably be fine. If it starts knocking mix in some higher octane or get it pumped out.

[@igorrosales1799]

@@SnubBarracuda Good advice thank you! Also idk if it helps but it’s in Denver and high altitude

[@tedwalker1370]

If the engine starts to ping, back off the gas pedal it should stop pinging. You are not going to be able to get the performance you are use to.

[@ShortArmOfGod]

If it starts to ping, it's already too late, champ.

[@TheBestYouthWrestlingVideos]

I wouldn't put 85 octane in my lawnmower.

[@GaryL3803]

You are correct, I would use 82 octane in a very low compression lawnmower engine.

[@gregpeterman1102]

No such thing as 85 in the Southeast.

[@dougchew5193]

The actual gas is 84 oct then the 10% ethanol boost it to 87 oct witch is added to the delivery tanker truck when loading, ethanol will attract water so they add it last

[@SaraK_69]

Uh, you should NEVER use 85 Octane in a modern engine! Any car made in the last 25 years cannot use anything less than 87!