Well, first an update on my 300SE saga. I got a second MB mechanic out to see the '90 SE ,charcoal/grey,and all seems fine. It may need a tune up in the next 10,000 or so the fellow said. But, before the MB mechanic got there guess what happened? the seller called to tell me that the first mechanic that looked at the car (the guy who said I need to change valves every 40k) called and made the seller an offer! The seller was surprised and called me to see what was going on. To his credit, he said he would not sell to the mechanic until I made my decision.

Anyway, my question is, is there a website for me to check to see the features of the 300SE in 1990 or an on-line owners' manual? I've been checking cars.com but their site is out of service for a while this AM.

Thank you all for your help. Hopefully I'll be an S class owner shortly.

Ron Brooks

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Thanks,
Ron Brooks

What exactly is it you want to know? I own a '91 300SEL - 1 yr. older than yours and 6 in. more leg room in the back seat - other than that - same car.

Change valves every 40,000 miles? Huh???

Maybe the guy was trying to scare you off so he could buy it and it seems he's now trying to do that.

My first question can be answered simply enough if anyone has an owners' manual. I have no problem using premium gas but I'm wondering if there is confusion over the octane requirements.

My last car was an '83 944. The owner's manual stated it required premium fuel with the minumim octane rating of 91. But, it did not use the R+M/2 method of calculating octane. It used the old method of calculating octane. The old method resulted in numbers 4 points higher than the research method used today as an industry standard. The end result is that the 944 required 87 minimum octane from today's pumps (which was the old 91). Now, the later 944 models raised compression and did require 'real' 91 octane from today's pumps. My '83 944 has a compression ratio of 9.5:1 The MB 1990 3 liter engine has a 9.2:1 ratio so I find it hard to believe that 9.2:1 requires a higher octane rating than a 9.5:1 engine.

SO, does the give the octane requirements for the 3 liter engine and the method used to calculate it? The manuals usually list minimum requirements and the method used for calculation as common info.

My second question is, do you know a website that lists the features in the SE or SEL?

OK, two more: how have you found ownership so far? and How many miles have you put on?

Thanks,

Ron B.

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Thanks,
Ron Brooks

'91 300-SEL owners manual specifies 91 octane gas. I live in an area where premium is rated at 93. I use it. Some here claim they have used the mid-grade successfully. I would not worry myself sick about the method used to drive the final number. MB said 91 and that's close enough for me.

If you want to asks questions about MBs, this is as good a site as I've ever found. Don't know about a website that describes vehicle features.

Does the owners' manual state whether it's 91 octane using the research method?

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Thanks,
Ron Brooks

I agree with Mike, don't fret too much over the specified requirements. Use what works for your car. If the engine starts pinging under low rpm/heavy throttle, switch to a higher octane. Unless your engine has a knock sensor, there is no benefit to running high octane except to avoid engine pinging.

Technically, octane requirement depends on a number requirements....compression ratio, ignition timing, and how badly the combustion chamber has deposits (resulting in hot spots and increase in compression ratio).

My manual specifes 91 octane. Locally I have available the 87, 89, ad 93 octanes. I use 89 without any problem.

I have a question to others....Is it possible my engine is pinging but the engine has so well built to suppress sound that I can't hear it?

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95 E320 Cabriolet, 159K