bad gas mileage 1978 450SL - Mercedes-Benz Forum

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post #1 of 4 (permalink) Old 02-12-2013, 01:19 PM Thread Starter
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Vehicle: White 1985 190D (my baby with 700,000 miles) Gold 1978 450SL, 2004 C240
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bad gas mileage 1978 450SL

bought a 450SL last year...a Gold 1978 and it is gets HORRIBLE gas mileage...I was wondering if there is any way to improve that. My 190D uses about 1/3rd of a tank of fuel on our trip home from Cumberland, which is about a 4 and a half hour trip. Our Ford Sport track made it on a half tank...the Dodge Ram made it on a half tank and the 450SL made it in 1 and a half tanks of gas...that is ridiculous gas mileage...about 11mpg to be more exact. I was told that there is a switch or adjustment under the floor mat or something, which is not there anything else I can do or am I doomed to not be able to drive it because I cant afford gas?
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post #2 of 4 (permalink) Old 02-12-2013, 03:57 PM
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Originally Posted by viperious View Post
about 11mpg to be more exact.
That good? I'm surprised it's in the double digits.

You might get a few more mpg in the summer. How do you drive it?
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post #3 of 4 (permalink) Old 02-12-2013, 06:15 PM
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A switch under the floor mat? Not to my knowledge...

I'd start with a basic tuneup and setting the air fuel mixture to correct levels. My dad had the same issue and he found a gummed up warmup regulator. They're expensive to buy, if you can find them, but the innards are accessible. In his case, he opened the thing and cleaned a bunch of gunk out of the thing. I think the best he gets now is 15 mpg.

There's another forum on this site dedicated to your car - lots of activity and knowledge you can use. It's through them that I found the warm up regulator idea.

Something I learned, and that pop learned the hard way is that the air/fuel mixture adjust is EXTREMELY touchy. SMALL turns of the thing will have big effects. He made the mistake of turning the screw a couple times, thinking he'd see gradual changes. He had to take it to the local Benz mechanic to unscrew (pun intended) his work.
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post #4 of 4 (permalink) Old 02-13-2013, 07:39 AM
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adjust the ign timing a little more advanced [ 5 deg or so ] , then you need to set co , here you need a exhaust analyser , set it on the lean side , and see how car run . on freeway , driving at 65 , you should do 15 mpg .
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