Mercedes and Octane Requirements - PeachParts Mercedes-Benz Forum

MB-Dude · #1 09-13-2007, 11:21 AM

While doing a little research for my posts in the thread Mercedes & Gasoline (http://www.peachparts.com/shopforum/showthread.php?t=199694), I ran across this information as to octane requirements in MB gasoline engines. I pass it along so folks will know that not all pre-1986 MB gasoline engines *require* premium gasoline.

{From the Factory Approved Service Products September 2006 bulletin, pages 7&8}

Gasoline Engines
Reformulated gasolines (RFG) and/or unleaded gasoline containing oxygenates such as Ethanol, TAME, ETBE, IPA, IBA, and TBA can be used provided that the ratio of any one of these oxygenates to gasoline does not exceed 10%. MTBE may be added up to 15%. The ratio of Methanol to gasoline must not exceed 3% plus co-solvents.

Mixtures of Ethanol and Methanol must not be used. Gasohol, which contains 10% Ethanol and 90% unleaded gasoline, can also be used. These blends must also meet all other fuel requirements such as resistance to spark knock, boiling range, vapor pressure, etc.

Gasoline Additives
Of major concern among various engine manufacturers is the carbon build-up caused by gasoline. MERCEDES-BENZ recommends using only quality gasoline containing additives that prevent the build-up of carbon deposits.

After an extended period of using fuels without such additives, carbon deposits can build up, especially on the intake valves and in the combustion area, leading to engine performance problems such as:
• warm up hesitation,
• unstable idle,
• knocking /pinging,
• misfire, and
• power loss.

In areas where carbon deposits may be encountered because gasoline with additives are not available, Mercedes-Benz recommends the use of additives approved by us for use on Mercedes-Benz vehicles (page 15).

DO NOT blend other fuel additives with the fuel. These additional additives only result in unnecessary cost and may be harmful to engine operation.

Damage or malfunction resulting from poor fuel quality or from blending additional fuel additives other than those tested and approved by us for use on Mercedes-Benz vehicles (page 15) are not covered by the Mercedes-Benz Limited Warranty or by any pre-owned or Extended Limited warranties.

Premium Unleaded
Use only premium unleaded gasoline meeting ASTM standard D439. The octane number posted at the pump must be at least 91 min. In the U.S., this octane number is an average of the Research octane number (R) and the Motor octane number (M): (R + M) / 2. The octane number is also known as the Anti-Knock Index.

As of model year 1987
All gasoline engine models require premium unleaded gasoline.

Model year 1986
All gasoline engine models, except the 190E 2.3 require premium unleaded gasoline.

Model years 1975 - 1985 and model year 1986 190 E 2.3
Use unleaded regular gasoline meeting ASTM standard D439. The octane number posted at the pump must be at least 87 min.

Model years 1972 - 1974
Use leaded or unleaded gasoline meeting ASTM standard D439. The octane number posted at the pump must be at a minimum of 87. When only unleaded gasoline is being used, check the valve clearance on engines with mechanically adjustable valves at half the recommended interval.

Pre-model year 1972
Use premium unleaded gasoline meeting ASTM standard D439. The octane number posted at the pump must be at a minimum of 91. Check the valve clearance at half the recommended interval.

Flexible Fuel Vehicles
Flexible Fuel Vehicles - As of Model year 2003 - 2005
Use premium unleaded gasoline (see gasoline engines) or Ethanol (E85) fuel to operate Flexible Fuel Vehicles. Models capable of operating with E85 are identified by a label reading Premium gasoline or E85 only! on the fuel filler flap. For information on Flexible Fuel Vehicle operation, refer to the Operator’s Manual.

{End of bulletin excerpt}

With the except of MB’s stance on gasoline additives (2001-no, 2006-yes), this information is very consistent with the same section in Factory Approved Service Products November 2001 bulletin, suggesting there has not been a change in their view of octane requirements.

Cheers,
Jeff

CamelotShadow · #2 09-13-2007, 01:06 PM

Thanks,

Interesting read

I have a 83 500 SEC Euro so not sure of compression.
The 380 manual said 91 octane

Last tank I got Chevron Prem
There octane ratings are 87 89 91
They have no 93
It would appear only the premium has the techron additive.

Also confusing is the units of measure
so you can't just go by number alone

My car sat a few years so I'll give it the Chevron tech & pay the addtl cost just for the peace of mind.

Rockman59 · #3 09-14-2007, 11:52 AM

MB Dude's article said: Model year 1986. All gasoline engine models, except the 190E 2.3 require premium unleaded gasoline
_______________________________________________________________
I have a 1986 560 SEL with 156K miles. This car has had nothing but regular unleaded fuel and it runs fine, gets decent mileage and has had no engine problems. That being said, if you drive your MB hard and fast or pull a trailer or do things that put the engine under heavy load, premium fuel is the way to go. But for normal everyday driving you can use regular unleaded.

MB-Dude · #4 09-14-2007, 05:59 PM

Quote:

Originally Posted by Rockman59

MB Dude's article said: Model year 1986. All gasoline engine models, except the 190E 2.3 require premium unleaded gasoline
_______________________________________________________________
I have a 1986 560 SEL with 156K miles. This car has had nothing but regular unleaded fuel and it runs fine, gets decent mileage and has had no engine problems. That being said, if you drive your MB hard and fast or pull a trailer or do things that put the engine under heavy load, premium fuel is the way to go. But for normal everyday driving you can use regular unleaded.

Please be aware I am not making a statement as to the usability of regular unleaded. I simply wanted to post what the 'official' Mercedes stance was, so that folks can form their own opinions, based upon their particular circumstances. Some people are using premium, simply because somewhere along the line someone told them ‘Mercedes only take premium’.
Cheers,
Jeff

lkchris · #5 09-14-2007, 06:08 PM

Many Mercedes are 3.0 liter which means 180 cu in.

Many American V8s are 6.0 (5.7) liter which means 350-360 cu in.

For the Mercedes to make the same horsepower--and it often does--requires higher rpm and higher compression.

Higher compression requires premium fuel.

This is not an opinion and no one gets to "decide" for themself.

RConrad · #6 09-15-2007, 11:04 AM

Dude:

FYI-I have a 96 S-320 and have used REGULAR since new. Now at 92,000 miles with no Ill effects. Newer cars have computer controlled everything, including the spark control, etc. which will adjust for whatever. I would agree that if you drive it hard/tow etc, might be a good idea to use the premium then. FFT

Ron