rockit31

Hello everyone. New owner of a 2012 GL450. Loving this beast of a car! First question, manual says only 91 octane or better, but fellow Mercedes smaller suv owner says you don't have to and it will run just fine. Thoughts?

chassis

Welcome! Please post a photo of the GL.

German vehicles are developed in a land where 95 Euro octane / 91 US octane is the norm. Using the manufacturer's recommended fuel helps achieve manufacturer's warranted performance. Using lower octane fuel is the choice of the operator. I suggest following M-B's recommendations.

BlownV8

Will run fine on regular. Been running regular for over 150k miles.

Max Blast

Have you had this change accommodated using an MB STAR/DAS tool?

There's a largely unadvertised option for running 87 octane within the engine management menu for those customers living in areas where premium is not available - it just sets a max conservative ignition map for use with lower than 91 octane fuel; lowering the risk of detonation.

Pre-detonation is very bad for our all-aluminium engines.

Max

lkchris

Mpg is reduced as ignition is retarded. So is power.

one should be proud to own a super efficient engine, that is an engine with high compression that maximizes simultaneously both power and efficiency.

TINSTAAFL

DennisG01

Took me right back to my 12th grade Economics class in 1990!

I've been using 87 octane in my BMW (same basic recommendations as MB) for the last 10 fillups. I have noticed zero effects on power and mpg - and I keep very accurate, recorded data on my mpg. I was skeptical, at first, but now I don't even hesitate and all my fillups are 87. Personally, I wouldn't do this with a low mileage car, but I think it's a safe bet that as the cars get older, the compression drops a bit. Can't say for sure as my BMW still seems to have the same get up and go - according to my 0-60 times vs published 0-60 times - but I'm satisfied with the 87.

TX07GL450

In March 2019, I drove from Houston to Sacramento, CA and drove back. I used 87 while going there and 91 on my way back. It was about 1930 miles each way
My GL had 91K miles at that time.
I calculated the mileage and it dropped about 4 mpg with 87. It was 22mpg on 91 and 18mpg on 87. I didn't notice much difference in power or handling.
so my personal result- 87 gives low mileage than 91.

BlownV8

I've suffered no noticeable difference in MPG's and that's an average over many tens of thousands of miles. Just started using 87 around the time gas was spiking above $4/gallon and never went back. Now, if you tow or drive very aggressively, I recommend you stick with premium.

Miguk_Saram

For a bit of perspective:

Based on current fuel prices in the Washington, DC suburbs, the fuel cost difference for both one-way trips is approximately US$3.83. It would seem that, by going with the lower octane, the cost savings are negligible.

The math (numbers rounded off):

• High octane, $3.29/gallon (less fuel, higher price per gallon)
  • 1930 / 22 mpg = 88 gallons of fuel consumed
  • 88 * $3.29 = $289.52 in fuel charges
• Low octane, $2.67/gallon (more fuel, lower price per gallon)
  • 1930 / 18 mpg = 107 gallons of fuel consumed
  • 107 * $2.67 = $285.69 in fuel charges

Difference: $289.52 - $ 285.69 = $3.83 saved.
And an extra stop to refuel (107 - 88 = 19 ==> one more tank of fuel).

Personally, I'd stick to the manufacturer specification. Not sure how this would work out for city driving, but I'd suspect it's not that far off.

Just sayin'....

CharlzO

Not discounting any math or other experiences. However, the cost savings are only negligible if you're experiencing a drop in MPG between them. I don't compare octanes unless I know I'm taking the same exact routes and road conditions. Sometimes, just different directions can affect MPG. I have a 3 hour drive that I make each weekend for example, and there's a 2 mpg difference between direction, even at the same speeds via cruise control. And when I went west and south this summer, it was a noticeable difference in mileage going down than coming back up home. In my experience, I've had virtually no difference in MPG between 87 and 91/93 octane fuels. And in some stations around here, there can be up to an 80 cent difference from regular to premium. Couple that with a 25 gallon fill-up, and you're at a $20 dollar difference per tank. Using your figures above, rounding to 4 tanks of gas per trip, and now it's closer to a $100 difference, not $4. I'm not arguing real world numbers from other people, but not everyone's experiences are the same either.

I think the biggest takeaway is that mechanically, the chances of it being catastrophic to the vehicle to use regular, is very slim. As for the mileage, run through a couple tanks of each, and see how you fare and go from there.

eric_in_sd

I got sick of arguing why the octane difference ought to be a problem, why it ought to be negligible, etc etc etc.

I did my own 1,000 mile test. I accumulated the miles and fuel cost (and price, therefore quantity). I paid attention to whether long trips were involved (there weren't any), and also whether there were significant differences in weather, and tried to make the gasoline source consistent. This was in summer in San Diego, when the weather is very consistent.

Results? Mileage with 89 octane was slightly higher than with 93. This implies the knock sensors were not retarding the ignition timing - so there was no knocking on 89 octane gas.

I've now gone about 130k miles on 89 octane. That would be a fuel cost savings of about $1,300.

(Math: 130k / 20 mpg = 6500 gallons; x$0.20 / gal = $1,300)

That's $130 a year, which buys a lot of coke and hookers. Not really.

eric_in_sd

Kudos to you for doing the experiment, but you neglected an important point: Prevailing winds are from west to east. You had a headwind going there, and a tailwind going back.

I think it's out on I-10 there are massive wind farms. Ugly as sin, but that's not the point. The windmills are all facing west.