Premium or regular? - Benzworld.org

elfkonig · 03-27-2003, 08:31 AM

I just came back from a trip to L.A. (from Phoenix, AZ, about 8 hours or so, including about three within L.A.) to visit a friend of mine who used to work for Mercedes.

We were talking about the energy crisis, etc., and the "need" to put premium on certain Mercedes vehicles, including the ML.

He told me that all MBs are designed, BY LAW, to use regular unleaded and that it is something of a gimmick that they are said to "require" premium gas. According to him, it is only in high-performance, race-designed cars that the Premium makes a difference.

With gas prices being what they are, I wouldn't mind saving a few bucks every time I fill the tank, but I will not do it at the engine's expense.

Any thoughts?

S4toML · 03-27-2003, 08:42 AM

Bruce · 03-27-2003, 01:09 PM

a search of this forum will show that this issue has been rolled out several times. take a look at some of the past threads and you'll get some interesting reading.

bottom line is that your engine can function with lower octane fuel, but it will adjust timing to do so. you will likely find an increase in fuel use, which will somewhat (perhaps more than) offset the savings in fuel cost.

little to no total dollar savings, and perhaps some noticeable unfavorable changes in performance makes many ml owners inclined to buy 91 or higher octane. (i can only get 93, so that is what i buy, not sure if that is a U.S. thing, or just local).

You can mix 93 and 89 octane in equal proportions (if the tank is mostly empty, but 10 gallons of 93 and fill the rest of the way with 89) and get 91 octane fuel (it really does work that way).

Ratso · 03-27-2003, 01:55 PM

But I run the cheap stuff an logged 19.7 mpg with mixed hiughway and city this week. I have primarily driven city @ 13-14 mpg +/-, but the stretch on the highway this week showed good results. I don't think the 93 is worth it.

rs · 03-27-2003, 02:00 PM

I get about 1 mpg better when I run 91 vs 87. 91 is $2.31 a gallon, 87 is $2.11. ($.20 for 1 more mile per gallon) However I usually gas up w/ 91 as I feel the performance is better.

randyman · 03-27-2003, 06:08 PM

i haven't tried using any octane rating lower than 91. for those who have used lower octane was there any engine knocking or pinging? i wouldn't mind using 87 if there is no knocking especially during WOT.

timf · 03-27-2003, 06:46 PM

In the past I have run my ML on 87, 89 & 91 octance. I have noticed no difference in performance or MPG, neither have I heard or detected any detonation (pinking) under heavy load or hard acceleration.

The engine control unit is doing it's thing and adjusting the timing as required for the various octanes etc.

For the past 20,000 miles or so the ML has been running on 89 octane with the very infrequent tankful of 91 as a 'treat'. So far so good....

Over in Europe high octane petrol is often considered a 'gimmick' and many people run on regular - so ignoring the 'recommendations' in the owners handbook.

I believe that high octane fuel is only really required for high performance turbo charged engines where the ECU 'may' not be able to re-act quick enough.

A lazy lumbering V8 as in an ML is more than catered for by means of the ECU.

FYI

I used to work for Ford Cosworth on F1 and Indy Car engine designing the ECU's for race purposes - so I figure I know when it's safe tp take an educated gamble. OK it's only a few bucks per tank full, but it's the principle ....

reboundman · 03-27-2003, 08:27 PM

I've been using 94 octane all the way since I took possession of my ML. I filled two tanks of 91 in the past couple of weeks (due to the gas price hike) and I noticed I needed to step on the pedal a lil more than usual just to accelerate the truck from 0. So now I decided to go back to 94 because I believe the lil $ is worth it...

Mac · 03-27-2003, 09:19 PM

I wonder what percentage of persons with leased luxury cars that are tuned to run on ethyl decide to disregard the manual because they are not in it for the long term and don't have the same stake or pride of ownership in the car. Probably a lot, and there does not seem to be a lot of engine problems experienced by subsequent owners because of it, so I'd guess the car has the ability to save itself from the potential hazards of lower octane fuels.

JGCs, for instance, are designed to run on regular, just like a Hondas: they have lower compressions and putting a higher octane in them actually is a waste and can result in poorer performance.

I'm not an automotive expert, but for towing, mountain driving or driving at altitudes, the results of flaunting the manual's recommendations probably will noticed much more than in easy driving situations. The ML is heavier than many cars and pushes a lot of wind and I'll probably own it for a while so the extra cost, to me, is part of the investment.

So far, at 65.5K, the engine doesn't burn a drop of synthetic between FSS intervals and I cannot take any credit for it other than giving the car an easy break in. It seems to me that using the proper fuel might also help keep the lubricants cleaner over time, which would be good for the life of the engine.

Darkmann · 03-27-2003, 10:25 PM

every car in the US is designed to perform satisfactorily with the lowest grade octane available. The engine management system will handle it just fine. You may see a drop in performance or mileage but your engine will be just fine. One of the main reasons the Mercedes requires premium gas is for proper emissions control. If you look at the compression ratio, I hardly believe that the ML320, for example needs premium fuel. Filling up with less than 93 octane will NOT damage the engine.