Hopefully not a major mistake on my 450SL - Mercedes-Benz Forum

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post #1 of 9 (permalink) Old 12-01-2014, 08:52 PM Thread Starter
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Hopefully not a major mistake on my 450SL

So I have been working on my 73' 450sl and today took it for a test drive, ran great and far better than expected for how long it had been sitting, the thing that concerns me is I put 8 us dollars of 87 (regular) gas in it, when I was told I should use premium ONLY because of ethanol in lower octane gas, Should I drain the tank or will I be ok if I put in octane boost and at least 20 bucks of premium (91)? Thank you anyone who can help me out and (hopefully) put my fears to rest? This car means a lot to me and I would be very sad to have broken it already :P
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post #2 of 9 (permalink) Old 12-01-2014, 10:09 PM
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I can't see that such a small amount of 87 would make any difference. Just fill it up with premium and enjoy your car
Cheers John.
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post #3 of 9 (permalink) Old 12-01-2014, 10:39 PM
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If it doesn't knock, you don't need premium. The octane is to prevent pre-combustion (knock).
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post #4 of 9 (permalink) Old 12-02-2014, 04:04 AM
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I ran my 108 for years on the cheap stuff without issue.
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post #5 of 9 (permalink) Old 12-02-2014, 04:48 AM
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My 1972 280 SE 4.5 has been running on 87 octane with ethanol ever since that blend was introduced - no problems whatsoever.
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post #6 of 9 (permalink) Old 12-02-2014, 05:26 AM
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US Spec 450sl is very low compression, 8 or 8.8:1 I can't remember. It doesn't need premium. I only run regular in almost all of my Old MB cars. The manual states that you can run lower octane fuel but might need to retard the timing (if you hear knocks). The spec timing on a 1973 450sl (5 degrees atdc at 750rpm idle with vacuum, 5 btdc without vacuum) isn't going to create any knocks. Then pretty much all the failure modes result in retarded timing:
- mechanical advance doesn't work --> retarded timing.
- points wear out --> retarded timing

Ok... Here's one that results in some advance, but isn't a big deal:
- vacuum retard fails --> 10 degrees advance at idle (to 5 btdc).

Ethanol is a real bummer, but the only parts I think it would ruin on a 1973 450sl would be:
- rubber fuel hoses (which always need to be replaced with time anyway)
- uhmm ... I can't think of anything else that would be ruined by ethanol on these cars. I tore one down to the pistons in the last few months too.

Hopefully not a major mistake on my 450SL-imageuploadedbyautoguide1417526640.172008.jpg
Hopefully not a major mistake on my 450SL-imageuploadedbyautoguide1417526671.905663.jpg
Hopefully not a major mistake on my 450SL-imageuploadedbyautoguide1417526708.860732.jpg


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post #7 of 9 (permalink) Old 12-02-2014, 06:33 AM
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zero issue there , if you really worry , you could add some octane booster , but you really dont need to , keep on driving .
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post #8 of 9 (permalink) Old 12-02-2014, 07:16 AM
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Yeah, as others have mentioned regarding higher octane, it's only there to prevent pre-ignition... knocking. As far as the ethanol part of the equation, I know there are a lot of complaints about ethanol, but it shouldn't affect the engine any worse than it affects everyone else's engine. I'm not sure if it burns hotter than non-ethanol gas, but your valve guides, seats, pistons, etc shouldn't be any weaker than everyone driving. If anything, MB engines seem to be more tank-like!
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post #9 of 9 (permalink) Old 12-02-2014, 11:29 AM Thread Starter
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Thank you for the replies everyone! All good to know, my step dad made it sound like the end of the world (Although he may have been messing with me as his weird way of saying good job getting it going)
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