this cool weather thing has me intrigued....

however, like I said...my faviorite station sells premium for 10 cents a gallon over regular.... 5 over midgrade...

so I will likely be back at premium next fill.... the car runs perfect on mid-grade right now in South Carolina.... I am also told we get "good" gas here...whatever that means...

Lee

My E320 (104) runs just fine on mid grade. 25 MPG on the highway, mostly highway driving. I know it offends the purists.

I also knew you'd catch hell for quoting our SC fuel prices. We have always been about the lowest in the country.

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Jeff

97 E320, ours 217,000miles
91 190E 2.6 daily driver 242,000miles
74 MGB,mine 120,000?
2006 BE350/Proline 21, 50 hours

I find it interesting that the price differential from regular to midgrade to premium is always 10¢ each step, no matter the price of regular. You'd think the differential would be a percentage. At these record prices, this makes filling with regular less attractive for engines designed to run on premium.

The Midwest has the highest prices in the continental US.

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95 E320 Cabriolet, 169K

well...I went through the tank with mid-grade....

at 300 miles 14.6 gallons.... did slightly better than I usually do with premium... I am fairly consistent at about 300 miles a week in mixed driving..

filled up with mid-grade again... gas is about 10 cents a gallon more than last week....

Lower octane fuel contains slightly more energy. With the manual tranny, I get 25-27 mpg, about the same as my lighter weight 2.2L Honda Accord.
Pretty amazing really.

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1986 300E 5-Speed 240k mi.

Although I agree with you on the energy issue, the experts here will not agree.

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2012 E350
2006 Callaway SC560

well, I am likely to stick with mid-grade until it gets hot or I detect any type of engine ping.

a co-worker has a 1991 300SpensivE. She has over 200k and uses nothing but mid-grade....

Larry,
Do you happen to have a chart of the different resistor values for the maps in the EZL? IIRC the installed resistor for U.S. is 200 ohms. I'm not so interestd in changing timing for lower grade fuel as I am in getting M103s to pass the ASM smog check. There is no way to retard timing on these as you well know. I've been using mid grade fuel in an 87 300E, 90 300E, 88 300SEL, 90 300SEL, and an 89 300CE without any problems, but I do use premium in the mountains.

Peter

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Auto Zentral Ltd.

I agree that lower octane gasoline MIGHT have greater energy. It will vary depending on the particular blend of gasoline required for each area/season, and at best it would only be about 1-2 percent, so measuring any decrease in fuel consumption would be difficult when you account for fill level and driving conditions variation.

Compounding the issue is the fact that oxygenated fuels have about 3 percent less energy than non-oxygenated fuels of the same octane number.

Duke

Switched from premium to mid-grade fuel two years ago. Mileage didn't change. Performance is slightly less but it is a 4700 lb truck with a v6. Never heard detonation and very familiar with the sound.

FR

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Fast Robert

Running 89 octane..
But when summer comes around, I run 91 because engine begins to knock.

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87' 300E champagne - Euro headlights and corners, 8-hole rims, 140,000miles/220,00km.

Read my post in this thread and also go to the link that I provided in this thread:

http://www.peachparts.com/shopforum/showthread.php?p=833484#post833484

Lower octane fuel in the moutains will probably create less detonation tendency than in the flatlands due to the lower air density at higher altitudes. The emission test numbers I reported are with regular unleaded and the test was done near sea level on a mid-sixties degree day. No detonation during the test. The only time I get detonation - and it's just transient - is if I load the engine at low revs from a short shift, but this only occurs at coolant temps above about 90C or ambient temps above about 75F. Where you live you could probably not use regular during the summer.

I actually need to remap the ignition advance curves. Since I did the work I read in the service information that the timing map is altered above 95C (It doesn't specifiy how, but one can argue that the timing is increased to cool the engine or it is reduced to limit detonation, and I suspect the latter.) and the coolant temp did exceed this value during some of the testing.

If you short the R16/1 connector and block the vacuum advance you will get very good emission test numbers due to the significantly reduced timing under the test load conditions. The NOx numbers really surprised me. I expected them to be lower since the reduced ignition advance will reduce peak flame temperature, but the 90 percent reduction really suprised me.

The car ran fine, except for being sluggish below about 2000 and VERY SLUGGISH below 1500. Above 2500 there was little SOTP difference. The low rev loss of torque will probably be less noticeable on a model with an automatic transmission since converter slippage will not allow a high load below about 2000.

Duke

I just put gas in my car and it was $2.85 a gallon from premium. Mid Grade was $2.75 and Regular was $2.65.

The way I see it, lets say I put in 10 gallons, thats $28.50, if I put in mid grade thats $27.50 and if I put in regular thats $26.50

It really only adds up to a small difference in price for me. I would rather pay way less, but since the car states premium unleaded only, thats what I use, and I pay the price unfortunately.

I know all those extra cents adds up over the course of a year to a decent amount, but I have used mid grade in my car before and regular, and my gas mileage suffered quite a bit.

Alon

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'92 300CE - Sold
2004 C240 - 744 - C7 Wheels - Android Radio
2002 C320 - 816 - Sport Wagon - Sold
2006 E350 Wagon - 368 - Dead
2015 GL350 Bluetec - 197U