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

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 :mad:

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.:D :D

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

If you can't afford premium...
 

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?

When I lived in CA the trick to getting a marginal older car through the emissions test was to put in Chevron's best with the engine real hot.
Woody

Nobody likes to pay high prices
 

What is the cost of a gallon of Starbucks coffee?

If you think our U.S. Congress is rotten, wait till you read this!

Do you know that there are 91 DIFFERENT FORMULAS of gasoline on the market in the U.S.A?
There are different formulas depending on the the EPA regulations in a given area. A case in point is the MANDATED Alcohol content in the farm belt. This mandate is to support the farmers and to be politically correct to get the enviromental vote!
g/f

a word to the wise - mid grade gas is their biggest rip off. it is cheaper to do half and half regular and premium that to buy this 89 Octane concoction that they sell...

89 is the same price as 87 here in MN. I run 89 in my new 2.6 190 no problems yet!

Kyle

In an answer to your question, I had a 94 Jeep that ran a little lean from the factory, and when going up a hill under load, if I rolled the window down while driving in the left lane which was also right against the hershey barrier, I could hear slight pinging.

Try to find a route that has the above, and you might be able to duplicate the results.

With your window down and even over 1 lane, you wont be able to hear it.

If you can duplicate it, take it even further, and experiment with different throttle positions, load pressures on the pedal, and different gears. Keep an eye on the r.p.m., gauge if equipped, you will learn a lot more about your vehicle this way, and hopefully get closer to your engine at the same time.

Kind of like Zen like...

Question fo Woody: Do you wash your car with surgical grade distilled water???,
After all, you're driving a Mercedes, so you should only use the highest grade available, Right?
JackD

Wow. Some bad advice in here. Its all about compression ratio, not performance. You may not hear it, but the engine can still have detonation, aka "pinging". Run what your engine calls for and go to Starbucks a couple less times per month to make up the "expense" difference. :) On a Ford 4.6L VTech ANY pinging will quickly destroy the oil pump. It practically disintegrates! I am not sure if an MB engine has any issue like that though.

If one spends $150/month in fuel. Premium is less than $30 more a month. Not a bank breaking difference.

As for gas companies telling people to buy premium. Never happened. Again, octane requirement is related to engine compression ratio. Thats all. I am sure gas companies call it "premium" for a reason, because they sure make a huge premium on it. But I really recommend you use what you should for any vehicle.

Side note: Some people like to "treat" their car with an occasional tank of premium. Bad idea if it calls for low-octane. The higher octane needs more compression to start a flame front properly. So the car adjusts. Then when you switch back, it has to adjust again. The entire time economy is impacted adversely.

Another side note: Did you know E85 is 94-98 octane? :)

Not a fan of Wiki, but this is a good read on knock/pinging/etc.

http://en.wikipedia.org/wiki/Engine_knocking

My opinions: we all have one - Ha.

The argument that if you drive a Mercedes you can afford an additional $300a year in preminum fuel does not hold water with me. An '87 300E is a $2000 car at best. I doubt anyone would consider running one of these very hard, and expecting it to live long, no matter what fuel it had.

Mercedes indeed goes a bit overboard in their maintenance and fuel recommendations. It's to their benefit; these cars are driven in horrendous conditions all over the world, and MB wants to push owners to the very best maintenance, to help them retain their reputation for reliability.

The resistor chip in US models retards the overall timing quite a bit, obviously don't mess with it if you are going to run less than preminum.

The '87 103 has no electronic knock sensor, and the timing advance is only adjustable by changing the timing resistor. And the US resistor is pretty retardant already.

The 103 has aluminum heads with 9/1 compression. That's pretty low.

You can definitely hear knock and ping in the 103. I heard it once in over 10 years of running 87 octane fuel. I wound it to 5000 rpm at full throttle on a 100-degree day, and picked up just a bit of ping as it went past 5000.
Otherwise, zero indication of any issues running 87 octane in hot Dallas summers with the AC runining wide open.
Continued ping and knock will show up quite obviously in most engines by checking the spark plugs. I can't knowledgably say this is true of the 103 because I check the plugs at least every 10k miles, and have seen no evidence of spark knock damage for the last 125k miles.
Maybe I have incipient knock and don't know it, but......

For me, running 87 octane has seemed to pay off. over 8000 gallons used, at an approximate 30 cents savings = $2400 saved. Enough to overhaul a 103 engine if it's getting damaged and falls apart at a mere quarter-million miles.

Just my 2 cents.

DG

we run mid grade in all of ours with no problems. Probably 250k in various cars over the years.

Just use 87 with stock timing. 91 octane when the temp gets above 90f aka summer.