Current Events > using premium gas when the manual 'recommends' it?

(+) Yeah! (+)

the owner's manual on my car 'recommends' using 91 octane, but says regular 87 octane won't hurt anything. apparently lower octane gas will cause engine 'knocking' and slightly decreased performance.

would you use premium for $1 more / gal, or just stick with regular 87?

Depends on how much you care for the car.

Dakimakura posted...

Depends on how much you care for the car.

what makes you say that when the manual specifically says 87 won't damage the engine in any way? i plan on keeping the car for like 20 years, so i want it to last and stay in good shape.

i am pretty car ignorant

My MDX says to use premium so I use premium. Yeah the cost hurts a lot but I'd rather have my car running as good and as efficient as it can be.

It depends on the engine. For instance my motorcycle is fuel injected instead of a carburetor. It needs mid grade, & once in awhile I should do premium to help clean the pistons & internals out while using some fuel injector cleaner now & then though. Additives & stuff can eventually gum things up a little, & higher octane will help keep things cleaner inside but you still have to do regular maintenance.

I have a Jeep. It says that I need to use Mid grade . However High grade just runs better for me.

Lil Bandit needs premium.

Giant_Aspirin posted...

what makes you say that when the manual specifically says 87 won't damage the engine in any way? i plan on keeping the car for like 20 years, so i want it to last and stay in good shape.

i am pretty car ignorant

There are other factors I cant remember. People can be finicky about their prized possessions. Probably best to just look it up.

All you need to keep your car in good shape when it comes to gas is to use Top Tier certified fuel (has more detergents than the federal minimum to prevent buildup better than the bare minimum). The only reason to use premium over regular in a car that only recommends premium instead of requiring it is if you like to drive it close to the redline as the ECU dials back either high-RPM performance, redline limits, or both when using regular octane instead.

My Acura TL says "premium unleaded fuel only" so that's what it gets.

Specifically the owners manual asks for 91 octane but since that's not available here, I go with 93.

If your manual recommends 91, and says 87 is still okay, then 87 is okay and you wont have to worry about engine knocking or anything like that (the engine is built to adjust the ratios for ignition for this lower octane gas). The only difference youll experience is lower gas mileage and lower performance.

Paragon21XX posted...

All you need to keep your car in good shape when it comes to gas is to use Top Tier certified fuel (has more detergents than the federal minimum to prevent buildup better than the bare minimum). The only reason to use premium over regular in a car that only recommends premium instead of requiring it is if you like to drive it close to the redline as the ECU dials back either high-RPM performance, redline limits, or both when using regular octane instead.

thanks. never even heard of "Top Tier" certified fuel. but it looks like something most gas stations around me use.

https://www.toptiergas.com/gasoline-brands/

i almost never take the RPMs to red line, or even close to.

TheSuperSilver posted...

Specifically the owners manual asks for 91 octane but since that's not available here, I go with 93.

yeah i dont think ive ever seen 91 around here, just 93.

IdiotMachine posted...

If your manual recommends 91, and says 87 is still okay, then 87 is okay and you wont have to worry about engine knocking or anything like that (the engine is built to adjust the ratios for ignition for this lower octane gas). The only difference youll experience is lower gas mileage and lower performance.

for real? the manual does specifically mention "knocking". is that something that will be really obvious?

My Mercedes has a minimum 91 octane requirement, so thats what she gets. Fucking around with that shit is asking for trouble on expensive cars.

Basically running lower grade fuel in a car that is recommended higher (only if stated allowed by the manufacturer) will just rely on how reliable the computer itself is with adjusting mixture and timing. I've never heard of it being an issue/failing, but my thinking is wtf would I buy such a car for if I won't commit to then fuel it should ideally take?

Like when I got a CX-5 Turbo over a standard. Why pay for that if I'm just going to put in fuel that detunes it like a loser?

Giant_Aspirin posted...

for real? the manual does specifically mention "knocking". is that something that will be really obvious?

Putting anything lower than what they say is okay (e.g., lower than 87, or E15+ fuel) will result in knocking or engine damage; though this won't be immediate (it'll take time, and it won't be a one-hit, you're fucked scenario; except for maybe putting E85 fuel in a car that cannot handle ethanol fuel). If you ever find yourself accidentally putting in like 85, and you're scared, you can go into the gas station and buy an octane booster bottle to put into your car. But like I said, you doing this accidentally here and there won't kill your car.

What car is this, anyway?

IdiotMachine posted...

What car is this, anyway?

2024 Integra

If it has a turbo I wouldn't skimp, otherwise 87 should be fine.

Giant_Aspirin posted...

2024 Integra

https://gamefaqs.gamespot.com/a/forum/f/fabe4c90.jpg

Your car manual literally says less than 87 will leave to engine damage; you're fine to do 87 if you'd like. Use 91 if you're going to take that car on a track, but 87 is good for normal use.

Also,

Giant_Aspirin posted...

thanks. never even heard of "Top Tier" certified fuel. but it looks like something most gas stations around me use.

Directly in the manual, it even talks about "Top Tier" lol. FYI: Costco gas is "Top Tier", but Sam's Club gas isn't. Does this really matter in a real sense? Eh...

The last car I drove that said it required premium was my 2009 Mitsubishi Eclipse GT. I tried using regular once and the fuel economy and performance was noticeably worse immediately. Switched back to premium and it ran smooth after that.

Mitsubishi sucks ass though so maybe your car will be fine

IdiotMachine posted...

Does this really matter in a real sense? Eh...

My engine is cleaner than your engine.

IdiotMachine posted...

Your car manual literally says less than 87 will leave to engine damage; you're fine to do 87 if you'd like. Use 91 if you're going to take that car on a track, but 87 is good for normal use.

87 was the lowest i was considering. thanks for the info!

IdiotMachine posted...

Directly in the manual, it even talks about "Top Tier" lol. FYI: Costco gas is "Top Tier", but Sam's Club gas isn't. Does this really matter in a real sense? Eh..

i see that now. i normally go to Shell, which is on the list.

voldothegr8 posted...

If it has a turbo I wouldn't skimp, otherwise 87 should be fine.

it is a turbo.

Modern engines will adjust the timing if you use lower octane than recommended. If premium is required it will say required, not recommended. Most likely the only negatives you might see is performance loss or lower fuel mileage. If you do hear knocking though, I would get premium immediately.

91+ octane fuel burns more slowly than 87 octane fuel. This helps mitigate engine knock (when the piston slams into the ignition flamehitting the flame too early, causing a knocking sound as it's jostled in the cylinder instead of being pushed straight down) in high-compression engines. Most engines nowadays are high-compression for better performance and emissions control.

When you use low octane, a modern car will adjust the timing of the spark plug ignition with the help of a knock sensor, so that the flame doesn't happen too early. It's unlikely that this sensor will ever fail. Cars without this knock sensor face damage from too much engine knock. I'm not sure how much is too much (10,000 miles of engine knock? Would it survive?). The damage is burned/soiled pistons or valves. In extreme cases, a piston might melt or develop a hole, after which it loses compression and becomes useless.

If you want to save a little, it should be possible to fill half with 89 and half with 93.

Giant_Aspirin posted...

the owner's manual on my car 'recommends' using 91 octane, but says regular 87 octane won't hurt anything. apparently lower octane gas will cause engine 'knocking' and slightly decreased performance.

would you use premium for $1 more / gal, or just stick with regular 87?

A good rule of thumb is to calculate the fuel requirement using your engine's compression ratio. Higher compression ratio = higher octane needed. Google gave 9.8:1 compression ratio for your car. That's a really high compression ratio for 87. For comparison I once used 87 for a commuter bike with 9.3:1 ratio. But 87 for 9.8:1 ratio? That's pushing it too far imho.

My suggestion? Use 91. Honda most probably mentioned 87 for marketing purpose. Not too mention the use of 87 came with a caveat about knocking and top tier fuel. Knocking is a sign of premature combustion tc; keep that up and it will wreck your engine.

The line '87 won't damage your engine' was written in controlled lab condition. 20 years road use like you planned is not lab condition and if you blamed Honda, they'd just say "can you prove that you always use top tier 87? also didn't we warn you about knocking?" They wrote that caveat for legal reason.

Giant_Aspirin posted...

it is a turbo

On top of what post 26 said, you should definitely be using 91 if not 93. Using 87 all the time will vastly shorten the life of the turbo.

appreciate the help guys.

I tend to use the highest whenever possible too :)

Why is there even a cheap engine destroying gas option available to begin with?

thisworld posted...

A good rule of thumb is to calculate the fuel requirement using your engine's compression ratio. Higher compression ratio = higher octane needed. Google gave 9.8:1 compression ratio for your car. That's a really high compression ratio for 87. For comparison I once used 87 for a commuter bike with 9.3:1 ratio. But 87 for 9.8:1 ratio? That's pushing it too far imho.

My suggestion? Use 91. Honda most probably mentioned 87 for marketing purpose. Not too mention the use of 87 came with a caveat about knocking and top tier fuel. Knocking is a sign of premature combustion tc; keep that up and it will wreck your engine.

The line '87 won't damage your engine' was written in controlled lab condition. 20 years road use like you planned is not lab condition and if you blamed Honda, they'd just say "can you prove that you always use top tier 87? also didn't we warn you about knocking?" They wrote that caveat for legal reason.

True about compression ratio - my car's engine is 11.2:1 so 91 octane makes sense.

The manual also talks about using less than 91 octane if it isn't available as a short term solution. It explains what the premature knocking is and that the car may experience that but to stick with 91 whenever possible.

So "just use sub 91 octane and deal with the premature knocking and engine/fuel performance" is not a responsible solution long term.