As a new owner of a 450 sl (1973) I am shocked at my gas mileage about (8) mpg. I should have known, living through the 70"s oil embargo. Does anyone know of a way to increase the mpg's. Thanks

My 4.5 was getting 6-8 MPG too when I first got it. Then while watching the odometer closely, one day I noticed it would stop registering miles after awhile. Since I was driving over known distances I kept a mental log of miles driven and guestimated my mileage. Started breaking 10 MPG.

Then I changed air filter, oil & filter, plugs and adjusted the valves. New fuel filter also, plus started it on a diet of Redline's Total Fuel System treatment. Plus had the speedo head rebuilt, and now log true mileage. Currently average 12.5-13 MPG city, and 15.5-15.9 MPG highway. You're not gonna get much better than that.

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Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

I concur with Mike's assessment on typical 4.5 mileage. I remember that the EPA city rating for a 1974 Oldsmobile Omega (Chevy Nova clone) with a 350 V8 was 9.9 MPG. This was an era when manufacturers were just getting their feet wet in terms of designing emission control systems for low-compression engines. Fuel economy suffered as a result.

Take comfort in the fact that the 450SL is built like a tank with real metal and realize that the price for all that extra weight and crashworthiness is just a few more gallons of gas.

And I cried when I got but 14 to 15 MPG during intercommunity driving and but 15.5 MPG on the freeway.

My 78 450sl gets about 8 mpg city/10 mpg highway. I've done a lot of things to try to get better mileage. I've replaced both the front and rear shocks, got new tires, replaced a badly busted connector pipe in the muffler (connects the left and right exhaust pipes coming out of each side of the manifolds...I had to fix it just because of the noise, but I also figured a more efficient exhaust would yield better use of power), but there is really not much improvement.

I also adjusted the mixture to run very lean, but because my car has an overheating problem, at the leaner mixture, the car was getting too hot too quick and hence dieing out at idle because of the hot engine; so I richened the mixture slightly to lengthen the time before overheat...although the overheating might also be causing lower gas mileage...theoretically speaking, I figure power is being converted to heat instead of engine torque...something like this.

I have a k&n air filter, fairly new 1.5k, but I really thought that replacing the shocks would do a good bit, considering the body is now evenly balanced on the chassis. I'm pretty sure I replaced original equipment shocks, so that had to be done anyway.

As you guys say, there's not much really more to do, but I'd be happier with the 12mpg that Mike is getting.

Next on the list is the fix the overheat problem, and also I'm gonna use some Seafoam in both the oil and the gas. Once I let the Seafoam work in the oil and supposedly clean up the crankcase, I'll change the oil again.