I have gotten a few diff. answers from the MBZ folks I respect.

No it's not mandatory just cost effective. You can retard your timing and have less power and less mpg but run 87 octane fuel. Or you can premium fuel and get more power, more detergents to kept injectors clean and better gas mileage.

That's just what I have heard I have never tested it but others have. The way I look at it premium has never been cheaper in comparsion to 87 octane. Remember back when regular was a dollar and premium was a $1.20 that's was a 20% premium. Now regular is $3.37 and premium is 3.65 that's only a 7.7% premium a real bargain.

Good point

I don't put anything less than 89 in my TE. I once put 87 in by accident and it was not a happy puppy. Never again. 99% of the time I put 91. With 87 I get a little less MPG so the savings of .10c a gallon close to cancel each other out.

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What's the compression ratio? That's usually the determining factor. 9:1 and below engines seem to only need regular gas. 9-10:1 engines typically require 91-93 octane gas.

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what about filling up with 89 and adding octane boost? You could save $$$ and still get the required octane?
My brother suggested this to me, but i haven't tried it yet....

If it's a USA engine, premium is definitely not necessary.
If it's Euro - which I was recently told by "mbdoc" is 9:1 and not 10:1 as I had previously thought - premium-or-not would depend on timing. If it runs without pinging, use regular. If not, use premium.
I was also told by a chevron guy that the same amount of techron is in premium as in regular. Further, I have done the math and to buy cheaper gas and a can of techron is more expensive than buying spendy chevron gas w/techron already in it.

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MB's that require premium say it on the cluster and by the gas cap.

I bet they like premium better though, I knew someone with a 1985 280te, and she was mean to it (always ran regular, did terrible maintenance) and it ran OK, but the exhaust smelled cruddy and it got terrible mpg's...(12)....she's a car abuser....and it died when an oil line burst on the freeway and she drove it another 4 miles to a rest stop, where it made noises...and seized. The car was real rusty though, dead leveling system, etc...interior bad...178k on it. She paid 5k for it, then spent 2k on all new brake system, and later another 2.5k on a new tranny, then 1-2k on fuel pumps and random fixes. It stranded her 5 times over the two years she had it.

So she spent about $12k on a car that she drove for barely two years, and put less than 15k on. Thats like 83 cents a mile! Not including gas and towing and such. Yikes. She then bought a new mazda.

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