Mid-grade gas
 

Well, I wasn't in the neighborhood of my usual gas station where premium sells for 10 cents a gallon over regular.

So for the first time ever in a MB owned car, I opted for mid-grade.

Even though we have some of the cheapest prices in the country for gas, I just couldn't pay $2.17 a gallon for premium.

We'll see how it goes. Typically I get between 19 and 20 mpg in my mixed driving week.

1989 300e 151k miles.

Depends on the engine. My 260E with 9.0 CR runs just fine on regular. Has for years. With higher CR or maybe super/turbocharged, it might matter. then again, most of theose engines have knock sensors. you'll never notice a difference.

KE-equipped engines of that era don't have knock sensors. Most will run on regular unleaded without detonation, especially in cool weather and coolant temperatures below 90C. In warmer temperatures or at higher coolant temperatures there may be some transient detonation at low revs/high load.

The specified CR of M103s in US models is 9.2:1.

Duke

$2.17 for premium would look good here in Oregon. That's about what we pay for regular and premium is up around $2.39. :eek: I'm also thinking about using a lower octane fuel around town.

I run midgrade in the winter. No troubles.

$2.17 for premium is a real good price! :D I think it is in the $2.30 range up hear.

Not to hijack this thread, but..... premium here is over $2.50 a gallon. Marathon's refinery is here - not 4 miles from my house.

You're more likely to get detonation "around town" than at highway speed including passing, since "around town" is when the engine is most likely to see the low rev/high load condition and higher coolant temperatures, which are the most likely conditions for detonation.

Duke

And we have it good here in the U.S. I've been in the UK on business a couple of times this year. On the way to a customer visit we stopped to fill up my coworker's car - a BMW 320D. Diesel was 95 pence per liter - the tab came to 14 Pounds for 15 liters. Thats about $28 for 4 gallons of fuel! A full tank costs almost $100.

On the plus side, a 3-series with a modern common rail diesel has surprisingly good performance and delivers better than 40MPG on the motorway.

- JimY

i have been paying around 2.59/gallon of premium lately.

last tank cost me close to 60 bucks. i think it was ~57 and change.

$0.10 per GALLON difference? We pay 12 cents per LITRE more for premium, which is about 45 cents per gallon.

Is this false economy? How much money are you going to save? Gasoline is not a major cost of operating a car. Depreciation is king!

Okay, suppose you drive 15,000 miles per year and get 20mpg. You burn 750 gallons of gas per year. That 10 cents difference adds up to a total of $75.00 PER YEAR or about $6.25 per month.

SIX BUCKS a month you're trying to save. Don't stop at StarBucks tomorrow.

Hey man...... I change my own oil, do all of my own repairs...... I am just seeing how the car runs on mid-grade.....

BTW, I make my own coffee in the morning as well.

That said, 50 weeks of the year I should be able to pass by my usual place and put premium in.

My car is probably darn near fully depreciated anyway.

Lee
Greenville, SC

Actually I think the manual says 91 octane and over is the recommended fuel.
Since most premium around here is 93 octane, I suppose one could mix a few gallons of 89 octane or even 87 octane with, say 3/4 tank of premium and still be over 91 octane, if it all mixed, totally evenly.
Not that I would ever do it with one of my Mercedes that has that "Premium Unleaded Gasoline Only" in black and white right under the fuel guage.
I paid 2.199 for the cheapest Hess premium in the area tonight, and regular was 2.039. That's 16 cents a gallon more than regular. Some stations are 21 cents more for premium; wow. I could save two bucks a tankful if it took regular, but I'd rather splurge a bit and not worry about pinging, knock, preignition, fouling plugs with those little metal droplets, etc.
Personally I'd rather save two bucks a week by using a coupon or two for lunch or something....

If you do get detonation and you are happy with a little less power, you can change the resistor that is located near the master cylinder to allow for burning lower octane fuel.

The euro cars have a dial that selects a different resistor to adjust for different fuel grades. US cars have a fixed resistance there. If you pull out the resistor it gives max advance and max power, but you have to burn premium fuel. By putting in resistance you can retard timing and allow cheap fuel to be used without detonation.

That said, remember that if you do that so you can run cheap fuel, that fuel will not take you as far down the road as advanced timing and premium fuel.

Good luck,

I'm currently running 87 octane and no resistor, which is the most aggressive timing map, and I'm not getting any detonation, but the weather is still cool.

Duke