Which gas octane number suits?

[gwuisman]

Reading posts on this site I sometimes notice that several US members tell that they use gas with octane 93. Here in Holland you can get octane 95 and 98. I’m always advised to use 98. 95 is the most popular gas and the cheapest. As our cars use a lot of gas, driving 95 would be welcome.  So I would like to be informed how the engines behave which are driven with octane 95 or even 93. My car is a US one with a not rebuilt engine and a euro ignition. Are specific modifications necessary? Can I use 95 without problems, will that result in fewer miles/km per gallon/liter or will I face engine problems/dammage now or in the future?

Gerard Wuisman
1970 280sl manual

[knirk]

My old MB mechanic contact here in Norway has always told me to use 98 octane and to use lead substitute additive. From previous posts I have read that you may use unleaded gasoline because the valve seats are hardened. Can anybody confirm this?
Even on my previous sl, a 1971 R107 350sl, I was told not to use unleaded.

Per G. Birkeland
69 280 sl aut 834
Norway

[n/a]

my statement is to always use the best available.  In the US, we have a different rating system, and 93 is typically the best available.  My question is "how many tanks do you use in a year?"....our car typically gets 2000-3000 miles a year which is maybe 10 tanks, which ends up being just a few dollars extra for the best gas each year...a no-brainer as they say.

-Lewis

66 230 sl 113042-10-016238
67 saab sonett II #43 of 258
00 saab 9-3 viggen conv
02 saab 9-5 aero

[Cees Klumper]

The W113 engines are (and always have been) fit for unleaded fuel. No need to add lead substitutes - apparently this has been confirmed by the factory and has been confirmed by experts repeatedly.

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[Ben]

I've used 95 for over 30,000 miles with no problems. I had the head off last year and there is no sign of valve seat damage/reccesion and the machine shop guy said "keep doin' what you're doin' "

I've heard conficting stories about the 350SL, maybe they were made of softer stuff !!

Regards,
Ben in Ireland.
'64 230SL 4sp.
'03 CLK Kompressor

[ja17]

Hello Gerard,
Here in America, most of us must use 93 or 94 octane fuel. The manual states that timing should be retarded a bit for every octane point lowered from the recomended 98 octane with 6 degrees being the maximum retarded. These US cars still can be set up to run very nicely.

The problem is that when you retard the timing you also will increase fuel consumption. What you save on fuel you may loose on mileage! So you may not save much and may loose a bit of power as a result.

All Mercedes engines have hardened valve seats and alloy valves after 1955 and will do just fine on no lead fuels. All US and Euro M130 engines had 9.5 to 1 compression unless specially ordered with a low compresson head. These 9.5 compression engines are designed to run on high octane fuel.

Joe Alexander
Blacklick, Ohio

[George Davis]

Octane ratings can be a little confusing, because there are three ratings: RON, MON and "anti-knock index" (AKI) which equals (RON + MON)/2.  One last semi-useful piece of information is that *typically*, RON is 10 points higher than MON, at least in the US.

I think the factory octane specification for the W 113's is 97 RON.

In the US, the best we can usually get is fuel rated 92-94 AKI.  But, since that is the average of RON and MON, and RON is typically 10 points higher than MON, then a 92 AKI fuel would have a RON of 97 (and MON of 87)... and thus would meet the factory spec.

So it's necessary to know the octane rating method in your country.  If it's RON (ROZ in Germany), then 97 or higher would be preferred.  If it's the (RON + MON)/2 rating, then 'probably' 93 or higher would be preferred.  It would help if you could get the RON number, but that doesn't seem to be easily available in the US.

In Oregon, where we reputedly have low quality gasoline (and one of the highest prices in the US, too), the best I can get is 92 AKI, and the car runs very well with no pinging at the factory timing specs.

Hope that's useful.  Do an internet search on "gasoline FAQ" for more info than you'd ever want on gasoline.

George Davis
'69 280 SL Euro manual

[Shvegel]

I keep my engine tuned to a fairly high level of performance and am unwilling to "detune" for poor fuel. I have been able to run Sunoco 94 consistently until this year.
  Judging by the high number of fuel related problems at the dealership I work at there have been some alterations to the fuel this summer that seem to have lowered the knock resistance to the fuel. This summer I am using 94 octane fuel with an added octane booster made by Nitros Oxide Systems.

[Joe]

I use 85 octane regular unleaded, and have no knocking or pinging. I've never tried a higher octane. Should I?
The car is tuned to BBB specs.
Joe
Colorado Springs
6035 feet above sea level

[George Davis]

Joe,

as I understand it, engines need less octane at high altitude.  If you have no pinging or knocking on 85, I'd say stick with it.  If you ever drive the car down to low altitude it would probably be best to use premium.

George Davis
'69 280 SL Euro manual