'74 450SL fuel

[bobmage]

Does anybody know offhand if the 450SL can run on non=leaded gasoline or must I add lead additives? Also what grade should I use in either case?
I just bought the vehicle and it has no owner's manual. Neither repair manual has that info either.

Thanks

[Catrinus]

The good news: yes, you can use unleaded fuel.
The bad news: you HAVE to use PREMIUM (unleaded) because MBs of this vintage simply don't run on anything less. Gets expensive, what with their pretty lousy gas mileage.

Catrinus
73 280C

[psfred]

All aluminum head and diesel (cast iron head) MB engines have hardened valve seat. Use of unleaded gas is no problem.

I'd also advise premium. You can try some midgrade (89 octane), but if you hear the slightest hint of spark knock, use premium -- there is a good chance that midgrade on the highway will fry the pistons. Not good.....

The D-Jet tends to run lean at speed from the high vac in the intake. This is good, as highway milage goes up to 17 or so (at least on my 280 SE anyway -- 16 in mixed driving), but if you are even slightly lean at off idle speed, this will mean over-lean on the highway. Bye-bye spark plug insulators and melted pistons.....

Peter

[erubin]

I have only used regular gas (87 octane) in my 450SL. It's the lowest cost gas available here in Los Angeles. The engine has 200K on it and valves have never been replaced. the car doesn't ping even on steep hills and accelerating. Timing is set to factory specs. I would put higher octane if it needed it but my advise is to only go as high as you have to to avoid pinging. using higher octane has no advantage except reducing detonation problems. I'm amazed at how many people use premium gas simply because they think it's better even though their engine was designed to operate well with lower octane gas.

[bobboyer5]

Peter:

Out of paranoid curiosity, how does one know if his pistons are fried?

What signs?

[brickyard]

My 1974 450SL is the only car in the family that runs on regular unleaded gas. Had it four years now and no problems. Researched this when I got it.

[bobmage]

Thanks for the info. I kinda thought when I noticed the compression ratio at 8:1 that it would run on regular, which is what I will put in the next tank.

[brickyard]

bobmage, one more thing. I've found that setting the timing at 5 degrees before TDC, instead of the MB spec of 5 degrees after results in much better performance, especially for in town driving.

[bobmage]

Thanks, I'll try it. Advancing the timing usually helps at this altitude andyway (avout 4500 ft)

[kip Foss]

I run my 1977 450slc on regular gas and I can go from zero to a speeding ticket as fast as anyone.