I would like some ideas about why it is necessary to run premium gas in a 88 300SE. I have run a few tanks of 88 octane and not noticed any knocking or difference in performance. Has anyone had good or bad experiences using regular unleaded in this engine?

If it calls for premium, use premium. You will not save that much using regular. The owners manual says that damage to the catalytic converter could occur if you do not use premium.

I also have a 2003 Escalade that has a 10:1 compression ratio and calls for regular gas. It has been burning regular gas for 90k miles. The M103 has a lower compression ratio of 9.2:1 and requires premium. I have to wonder how a 10:1 engine can run fine on regular but a 9.2:1 needs premium. I know it is only about a 10% savings, but people will spend a lot of effort and money to try to increase their gas mileage by 10% (20 vs. 22). I don't mind buying the premium if it really makes a difference. However if it doesn't really matter why waste the money.

Sometimes I wonder if expensive car companies specify expensive maintenance or fluids because it seems more exclusive and the original owners probably didn't care about the costs. I would guess that none of the diesels specified veggie oil, but a lot of people are using it.

Sometimes I wonder about this too

The M103 in the US comes with a resistor to 'retard' engine timing (or something to that effect) to supposedly compensate for lower octane gas. I might try and run 87 for my next tank of gas and see what happens

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2008 BMW 335i Coupe

When the diesels were built diesel was so cheap no one needed veggie oil. I dont think one would want to put veggie in a new diesel today.

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual

I found a post in a previous thread where jgood12006 said:

"If you do get a gasoline 300, DON'T run in on anything but premium or it will destroy itself."

I don't know if this was based on a personal experience, but I would like to know more if he is still out there.

An engine with a high compression ratio has some advantages. It squeezes more power of the same-size engine. But, it requires you to spend more for every tank of gas, to get that extra power. In other words, instead of manufacturing a car with a larger, but lower-compression-ratio engine, manufacturers are using high compression engines, and foisting the additional cost back to you — by forcing you to buy premium gas to get that extra performance.

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TX76513, I agree with your statements, but I don't consider the M103's 9.2:1 to be a high compression ratio. A basic Ford F150 is running 9.4:1.

When I had my 300SEL, it seemed like premium is all I could run it on. I tried the 89 octane a couple times, and it would ping like crazy during hard acceleration. :[

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Current cars:
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it was designed for premium.. stick to it that is the final answer unless you want to go out and spend a few grand on a new set of pistons and con rods

I looked through my W126 CD set and several engines have lower compression ratios. Does the 500 SEL - 116.960 engine require premium as well? It has a 8.0:1 compression ratio. If they recommend premium in that, I think it is fair to say that MB recommends premium in everything needed or not.

Dare you question a Mercedes Benz Engineers decision...

some of the earlier cars, well older than the w126 call for regular but seeing as the cars were made to be ran hard the fuel of choice is premium

Are you sure it was a MB engineer? I think it might have been a marketing VP's decision. I too am an engineer and believe it or not our marketing department doesn't always use the recommendations that we give them .

I only use premium in my 1988 300SEL and 1991 LS400, so I could not tell you any different.

As cheap as gas is now (that sounds funny doesnt it?), I would just use premium, but I know what you are saying.....

I only use 87 octane regular, no pinging or anything bad.

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85 300 SD ~ 115K
82 500 SEC Euro ??K
78 450SL 164K