I'd like to get an official response on this. With the ridiculous gasoline prices lately I have been putting middle grade, 89 octane gasoline in my 87 300E. Previously I religiously used super in this car.

I have seen many posts on this topic and most agree that it is OK. On middle grade my car runs well with no knocking or hesitation.

So how safe is this? Am I damaging anything or wearing anything out faster?

Thanx

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1987 300E

If I remember my Chemistry correctly, the lower octane gas will not harm your car. My only suggestion is do not drive it hard on lower octane gas. The motor is designed for performance, thus the need for higher octane fuel. You will have no damage to the motor by using lower octane (within reason) fuels in the tank as long as you do not drive like you're on a NASCAR track or try to race the teen-agers at the red light.

89 octane should be fine for highway driving or leisure driving... If you are stop and go in town, and runnig the A/C you should consider staying with the higher octane fuel.

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William
76 240D - 550K miles
78 300D - 200K+ miles

Most cars like yours will run on lower octane fuel ie; 91 octane. As long as under acceleration you don't hear the dreaded knock then why spend money you don't need to. Of course every 2-3 tanks filling with premium would make the mix a little richer in octane.

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MERCEDES BENZ MASTER GUILD TECHNICIAN
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 ITS RACECAR
1986 190E 16V

Had a 300E which I just traded in with over 170K miles. With a few exceptions always used 89 octane

All the previous replies are right on. I have used mid-grade in my 300E for quite some time. The key words here are "spark knock". If you hear spark knock, go back to the higher octane.

Good luck,

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Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

The oil companies are scamming people with all their ads suggesting everybody would be better off buying premium. Just keep your ears tuned for spark knock or ping and buy the lowest grade that doesn't ping.

can someone describe to me what spark knock sounds like, i know what ping is as ive heard it before but ive not heard of spark knock prior to joining the forums here .thanks

__________________
1984
190e 2.3L
107000 miles

The sad thing is in California, 91 RON is considered premium. About two years ago, it was 92 RON, and I could even find 93 RON at Shell.

Not so today

Our C36 engine does much better with the higher octanes (less retard).

neil

I have a 500sel '85 and run only 87octane. Everything else is wasting money.
Newer cars usually have electronic ignation with knocking sensors to avoid engine damage. If the sensor signals knocking (premature ignition of fuel/air mixture) the computer will retard ignition. You can do this manually on engines without computer. Get a strobe light and retard ignation a few degrees. Try out until you get an acceptable setting. It'll make your car slower on take off. You may not even feel it.
boili

I have a 500sel '85 and run only 87octane. Everything else is wasting money.
Newer cars usually have electronic ignation with knocking sensors to avoid engine damage. If the sensor signals knocking (premature ignition of fuel/air mixture) the computer will retard ignition. You can do this manually on engines without computer. Get a strobe light and retard ignation a few degrees. Try out until you get an acceptable setting. It'll make your car slower on take off. You may not even feel it.
boili

What about the effect of lower octane fuel on the catalytic converter ?? I thought this 87 to 89 RON stuff would ruin the CAT ? to say nothing of having the car exhaust smell !

If you do not have any knock or ping you will gain nothing by using the premium. Newer cars have knock sensors and they will retard the timing and lower the power, otherwise use the lowest grade that does not produce ping. If you are not getting any ping, then you will not get any more power from the higher octane. The car will be faster because there will be less money in your pocket therefor lighter, but I do not think that will make much difference in a big car like this.

__________________
Currently
1991 Mazda Miata 174000
1991 Subaru 189,000 Winter beater

got rid of:
1984 VW Vanagon 195,000
1976 350SE Euro 185,000 KM
1973 280SE 4.5 (boy do I regret that)
1980 280SE European W126 4 speed manual (miss it)
1989 BMW 735iL 119000 (good riddance)

I've been running 87 octane exclusively since the gas prices went to $2.00 a gallon in 2000. I haven't looked back.

__________________
1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T

Why are you driving a Mercedes Benz if you can't afford to put decent fuel in it? The extra mileage will probably balance the few dollars it cost extra for decent performance. If the newer cars retard the timing you will lose something. Why not buy one of those tin cans like a Geo Metro that get fifty miles to a gallon? You could save even more money! Unbelievable!
Woody

There was some discussion in other threads regarding the removal of a resistor or something that disabled the spark retardation capacity built into north american mb's due to our low octane rates (unlike europe); if one removed this device, i assume one should religously run with higher octane gas.

also, is it not the case that higher octane gas improves emissions (ie environmentally friendly) and would give improved results on an emissions test?