JethroAZ

Ok, here's a good one. Now I'm certain that everyone has been educated on this subject, but this guy hasn't so please lend your knowledge to the newbie.

My '08 ML350 owners manual states that I should use nothing but high octane (92) fuel in my car. Ok, I understand it's necessary as the factory documentation states, but is it absolutely required? Will my engine fall out or will it explode if I sneak in 89 octane once in a while? What would happen if I run 89 octane all the time?

QuadBenz

Your engine won't be running at its full potential.

Vernl

It also points out in the manual the ''allowable exceptions'' when the proper octane isnt available...running with out it causes engine sensors etc to run at less than optimal ranges and can cause problems with the cat system and O2 sensor etc in the long term....also would likely void your warranty when they determine why there was trouble

lkchris

The words "recommended" and "specified" have two different meanings.

For Mercedes, premium is specified.

https://mbworld.org/forums/attachmen...june06star.pdf

ninjajim4

i just don't understand why people buy these cars but then want to get away with saving 3 dollars at the gas pump.

aggst1

+1
And they ruin the motor and when they get stuck with a huge repair bill they blame the brand.

Folks! MB does not get a kickback from the oil companies to say Use Premium gas ONLY.

JethroAZ

Hey, Ninjajim, it's not a matter of saving 3 dollars at the pump since I drive that particular car only about 4 thousand miles per year. It's a matter of me having lent the car to a visiting vice president of my company who drove it around for 2 weeks then revealed to me during our ride to the airport that he only put in mid range gas since he's done the same from day one with both he and his wifes car without any issues. Both of which happen to be, you guessed it, Mercedes. I've been putting in 91 octane since driving it off the lot, but wanted to know if there was any wisdom hidden within his statement. For you to presume another motive was a waste of your time.

ninjajim4

at the risk of sound uncivil here.. WTF are you talking about??

you ask this:

and this:

first, what other motive could there POSSIBLY be to switch from premium to mid grade, when you clearly know your car is supposed to run premium? gee, how presumptuous of me

secondly, no there is no wisdom here, your VP is not only a cheap ***, but also an inconsiderate one and you shouldn't let him drive your car anymore.

aggst1

Owners manual states that if for some reason premium fuel is unavailable to use the highest grade possible. A while back I was out of town and was running out of fuel. The service station I found was put of premium so I bought two gallons of regular so I can make it to the next station where I filled up with premium. So, just try not to use low octane unless you have no choice and then try to limit the amount consumed. As a previous poster said there are sensors that adjust themselves for proper burning and the engine is not as efficient. Btw your boss IS cheap!!!

JethroAZ

There is no doubt that the guy's a cheap *******, and yes, I should not have loaned him the car, but what's done is done. I was thinking that by my posting what I did, I would be able to learn something and perhaps even get the facts about a topic that not only I, but perhaps other people were thinking of. To have someone state "I don't understand why people buy these cars but then want to get away with saving 3 dollars at the gas pump" didn't help me get any closer to obtaining the information that I was looking for, nor did it help anyone else.

aggst1

Let me put it another way. The car will function but not at its optimum performance. It's like someone smoking a cigarette. One won't do harm but over time...

JethroAZ

Perfect analogy. I'd like to send my boss this string to show him what he's actually doing, but he's the kind of guy that tends to only listen to himself. That and of course I called him a, well, you get the picture.

ohlord

boss is from Denver where 89 is equal to high test.
With your heat and 1000ft altitude 91min will always pay in performance and mpg gained v.s. the savings he tried to achieve with the odds being he is not living above 5000ft.
He will be working for you someday

ninjajim4

it sure does. if someone asked if they should put 93 in a car that requires 87, i would say don't waste your money. someone comes around asking if it's ok to put in 89 'once in awhile or all the time' in a $25k high compression german engine that demands 91+, i'm going to say don't be cheap.

if you can't read between the lines (a valuable life skill), that means put what you're supposed to put in your car. i guess i could have said it's going to retard your timing and pre-detonate under load, but the bottom line is exactly what i said. don't be cheap (the only reason you would do this, outside of exceptional circumstances). if there is some other motive, i'd like to know what it is.

BTW, i think if you framed this question differently we'd have been having a different conversation. obviously as is, there's no way i could've known, but nonetheless i apologize for presuming your boss' cheapness was your own

559EVO

It should be fine, my dad did that to my car once and when I asked him why he told me thats what they put on all the cars. He works for Mercedes at the shipping facility near long beach. I still always use 91.

waikoloa 320

I have read in the owners manuel using lower grade fuel doesn't burn up all the fuel. unburned fuel ends up in the caytalic converter which eventually clogs it up resulting in lost power and having to replace it.

craiger13

Well I am wondering about 93 because thats what I put in mines is that ok?

rescue48

Here's a little twist to this. We bought my wife a C300 and have been putting in the top stuff ever since bringing it home. I even educated myself on the "Top Tier" designation and only buy the 93 from the listed companies.


This past Monday we picked up a ML350 for me. So in talking to the sales rep... the SALES REP no less. He says something like "Oh that's no big deal. I get a new one every year or so, on lease and never put the good stuff in it. I only put the cheapest stuff in it." So I'm thinking, well you lease it buddy. What do you care? I keep my vehicles for a very long time, and don't want to take a chance at hurting the performance of the engine, sensors, or possible repairs.


To take a little angle on the "save $3.00" comment, I do look at it this way; If the cheap stuff costs $1.75, and the premium 93 top tier costs $1.95 and I get ten gallons, then it really is only $2.00 more to buy the good stuff and keep my beloved Benzes running at their designed peak performance. That's the way I look at it. It's not very scientific, but rather practical to me.


We buy the premium synthetic oil for the engines, so we should buy the premium fuel too the way I look at it.


http://www.toptiergas.com/

marc hanna

Use the grade of fuel your engine is designed for. It's a no brainer: higher compression engines require more refined fuel.

Fuel should be ron+mon/2 = 91

Some retailers only post ron, others mon; most ron+mon/2.

Higher octanes than what the engine is designed for offer no benefit because there is actually less stored energy.

Fortunately, modern engines are smart enough to detect knock and can adjust accordingly, but you do run the risk of going into limp mode.

Elchins

Did you ever check octane rating with octane checker before fueling premium unleaded 95 ? Probably not & this does not mean that every time you must check this. But, i do not trust for most stations stating premium octane.

pjw1967

The compression ratio in our '14 ML350 is 12:1. The compression ratio in my 1967 Pontiac GTO is 10.75:1. While I have never tried to run gas at less than 93 octane in the Goat, the timing has gone out sometimes and the knocking sounds like someone was dumping ball bearings into the cylinders. As stated above, your engine will adjust to the lower octane. You won't hear the knocking because the knock sensors adjust the timing to prevent it, but you'll lose a certain amount of power, which won't be really noticeable either. Proof of that is you didn't mention feeling it. I have never seen any published about the long term effects of running less that prescribed octane in a newer car. I would like to know who decides whether 91 as recommenced on my gas tank filler cap is available vs 93. In Texas where I buy gas the highest octane is 93. We went to the Winstar Casino in OK last year, and the gas station on premises had 91 as the highest. You would think that might be less expensive than 93, all else being equal. Who decides what's available, 91 or 93? I buy 93 at the local Costco. This past Sat 93 was $2.75. On the way to golf on Monday, a local station had 87 for $2.49 and 93 for $3.39. For those of you who deride someone for looking to save money, we are targets for ripoff artists. 20 gallons would be a $13.00 diff between Costco and the local. I'd cheerfully put 2 gals of regular in my car to avoid getting my pocket picked.

lkchris

It's a matter of altitude ... here in 5000 ft asl New Mexico, best we get is 91. It's just fine.