Old man at the Benz dealership says he’s been driving the same car for a long time and usually only puts in 87 octane in sprinkled with 91 every few times. What problems could this cause? Do I have to put in 91?
Disclaimer: I’ve owned (paid off) the car for 6 years and do put in 91, but trying to cut costs.
On newer cars? Slightly less torque, slightly less fuel economy.
On older cars? Some pinging at high loads like towing or going up a steep incline.
On modified high performance turbocharged or supercharged cars? Catastrophic failure if pushed too hard too long.
My car isn’t modified but the manual says it will cause engine failure and override any form of factory warranty if 91+ isn’t used. Is this a hoax?
This happened to me, not bad fuel but too much boost.
Ouch, too much boost is definitely trouble. The primary goal of the performance tuning process is slowly raising boost to within the limits of the engine durability, fuel system capacity, turbocharger limits, and fuel octane. Uncontrolled over boost can crack pistons, blow rods through blocks, and generally never end well.
If the car is designed for/recommends 91 octane and is not modified, use 91 octane. Presuming this is a relatively modern car:
Using a higher octane than recommended is wasteful and you won’t see any benefit as the car can’t “take advantage” of the higher fuel grade.
Using a lower octane can cause poor/reduced performance, reduced fuel mileage, and increased deposits inside the engine due to an incomplete/in burnt fuel mixture as the vehicles computer will likely sense the lower grade fuel (through knock sensors) and adjust the ignition timing to prevent major engine issues.
I’ve also personally tested the savings on a few vehicles I’ve owned that require 91. Switching to a lower grade fuel only results in a few dollars savings per tank, but also got notably reduced MPG, negating any savings. In a 20 gallon tank, you’re usually only saving $6-$10, depending on the cost difference between 87-91.
My 2019 with GDI and turbo runs much better on 93 octane, even though the manual says that 87 can be used. On 87 engine lags and the transmission seems confused for what gear to be in, none of that happens with 93, ( 87 and 93 are the choices where I fuel up ).
Only used 93 premium even if the manual said to use 91 only
93 is not available everywhere hence mfg recommendations say 91+
91 is mainly available in higher elevations since 93 is not needed, so that 93 youre putting in does absolutely nothing, youre just paying extra out of pocket
same goes for econo shit boxes that you think is a race car because you put a 4" fart pipe and a weak ass looking high rise spoiler. if it requires 87, putting in 91+ wont make a difference in the world
Reduced performance and economy. You’ll usually get better mpg with the recommended fuel so its best to keep using it. You might have some other small issues but it takes years of using the lower number to actually cause issues.
If it says REQUIRES 91, then you will have misfires, trouble starting, drastically reduced power and economy, and engine problems after a while
If you’re trying to cut costs, you could sell the car and get something more economical.
Everyone’s right about the minimum octane requirement as stated by the factory to mitigate knocking (bad) or a pull back in timing (resulting in no damage but lower performance).
However, there’s another advantage of using the highest octane fuel, which is cleaning additives. Fuels are pretty much generic, but additives are proprietary. The higher octane fuels generally have more of these proprietary additives, so using them can better ensure cleanliness within your engine.
If you want the additives in all octanes use TOP TIER FUEL.
100% agree. Here’s a link to Top Tier fuels.
You can also run a bottle of injector cleaner through it every few thousand miles and save the prices at the pump
I had an old Audi years ago that I really couldn’t afford to put 91 in. It ran like shit and would barely work with 87
My 2007 X3 doesn’t seem to care. Lots of other shit breaking but nothing related to fuel or pistons after 100000 km.
I think you can use 87 and put in octane booster into the tank, at least that’s what Scotty says anyway
stop thinking and listening to scotty
Don’t worry it’s just the engine…
Nothing really just you will be down on power.
The Computer scales back the timing (Can’t use the proper “R” word) when it detects detonation & you lose some performance.
According to the guys on the TV show Engine Masters it makes almost no difference these days with computer controlled ignition systems. They dyno tested regular, premium, high test, Sunoco racing fuel which is 116 octane. There was very very minor changes in torque and HP. Overall HP gain was about 10 on Sunoco racing fuel but it’s prohibitively expensive. The conclusion was if it doesn’t ping regular is fine.
Depends on the car… My 92 buick that’s supercharger with an ancient obd1 computer system with no knock sensor? I’ll mix 93/89 to get 91 but I wouldn’t risk anything lower since I don’t wanna crack a piston. Modern cars? High comp turbo engines can run 87 no issue.