1989 560SL - What Octane MUST I Use
 

I have a new to me, 1989 560SL with 52k miles. Filling the tank with 93 octane takes a bite out of my wallet.

Has any one used 89 octane with this car? Is this safe or foolish to do?

The concensus is pretty much "foolish".

If you want to use regular fuel, trade for a 380SL...:)

93 Octane, Wow. The best we get in Los Angeles is 91.
So maybe a mixing down would work.
My 86 560 runs fine on 91. For 91 we pay about $3.30 per gallon.
What the rate in Texas?

At about $4 difference per gallon and lets say 4 tanks a month. $12 to $16 (since gas prices vary) does not seem to be much per month to prevent an engine from detonating. Then again, I do not know the compression ratio of that engine or what it requires. Just say that its not like there is a 50 cents or more gap between grades. Usually its about 15 cents in my area.

Today: 87 octane: $2.49, 89 octane: $2.59, 93 octane: $2.79 (supermarket brand), add $0.02/gallon for Exxon or other majors.

23 gallons = $53.27 / $59.57 /$64.17

At 23 gallons, no clue on capacity, then your hitting a spread of about $10 per full tank.

Weird that premium is a 20 cent jump. Here is usually 10 cent between grades with many stations actually selling premium at mid-grade pricing.

There's a resistor that retards the timing by 6 degrees in the ignition system. It is located on the driver's side, under the hood. It was put there to allow it to run the lower grade without pinging.

I don't recommend doing it often, but occasionally wouldn't hurt.

I pulled the resistor and mix my own fuel with toluene (methyl benzine), which increases the octane of the fuel.

Here in Utah, 91 is the highest I can get without going to the local airpark and using it as a mixer.

I mix toluene at a 10% mix with gasoline. A 10% mix increases octane to roughly 95.

I had to start mixing my own out here, as our state only checks the ratings once every 5 years, and you can't be guaranteed what you're getting out of the pumps.

On one of my other cars, which is boosted, I run a 20% mix, giving me 99.1 octane.

Ahhhhh!!!:D:D

Now I know why the Euro versions run with so much power!

In the UK we can only get:

"ordinary/regular" 95 octane

and

"Premium" 98 octane

Seriously though - as jplinville says - the US versions are fitted with the resistor to retard the ignition 6% so you CAN run on poor grade fuel/gas/petrol as that was/is all that was available in some states when the 107's were sold new.

In the UK I use 95 RON most of the time but give mine a treat with some 98 RON occasionally - especially if I'm going on a longish trip - it does more MPG on the better fuel though not quite enough to compensate for the extra cost.

Just to make you all feel better "over there" 95 octane is around £1.13 ($1.75) depending where you buy it at the moment and 98 octane is around £1.21 ($1.88) - THAT'S PER LITRE!! 4.45litres to the UK gallon!!!!!

Happy motoring:)

6 degrees? Wow. That with all the cats, I can see why these are dogs when compared. I think I will pull mine and see what happens. We have 93 octane at many stations up here.

From the wikipedia.....You can look it up for more info. But essentially US octane rating is lower than European for exactly the same gas.

In most countries, including all of those of Australia and Europe the "headline" octane rating shown on the pump is the RON, but in Canada, the United States and some other countries, like Brazil[4], the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI, and often written on pumps as (R+M)/2). It may also sometimes be called the Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2.

Difference between RON and AKI
Because of the 8 to 10 point difference noted above, the octane rating shown in the United States is 4 to 5 points lower than the rating shown elsewhere in the world for the same fuel.

use as high as you can find, tune to those specs and you will be happy and not worry about the $$

I believe octane recommendations have to do mostly with the compression ratio of the engine. The higher the ratio, the higher the required octane. That's the same engine my SEC has in it, I believe. I think it's the M117, which is a higher compression engine.

yes but there are no cat's in the Euro models:)

I have pictures somewhere showing it's exact location and what it looks like, but I'm unable to locate it right now.

EDIT: Read post 4 in this thread for location and what it looks like... http://www.peachparts.com/shopforum/mercedes-benz-sl-discussion-forum/254366-juice-up-ignition.html?highlight=timing+resistor

Ya. I found it this morning. Took two seconds to pull. Just posted a blurb in tech. It really feels like another car. The throttle response alone is amazing. But I am going to go for 2 degrees to play it safe.