I added Shell's new additive to my tank and my milage went down 3 miles per gallon. Next tank no additive milage was back to normal, so I tried it again and the same thing - 3 mpg .
Has anyone experienced this?
For Sale Rotella fuel additive hardly used cheap.

I've had similar results with the Power RS stuff but the car is much easier to start in the sub-zero weather we've had. Car seems to run a tad better too. I lost maybe 5 MPG but the cold causes a lot of that so I've been told.

would cold air reduce MPG.

I would have thought (all things equal) that cold air = more O2 per cubic meter as it is denser (a reason for an intercooler).

So with more explosive o2 in there MPG should be better.

Better MPG at sea level etc.

Am I missing something?

Normally cold air won't reduce MPG, although it can increase horsepower slightly. What does kill MPG is the winter blend fuel, usually 5-15% depending on how that particular batch was mixed. It's very odd that the Rotella DFA hurt MPG that much. I was using it here as anti-gel the last few months (even though it never got really cold), and didn't see any drop in MPG. For the record, Mercedes doesn't recommend using any additive on a regular basis, i.e. in every tank. It shouldn't hurt to use some every few thousand miles or so, maybe at every oil change, but otherwise it's not really necessary. Of course adding anti-gel for you people who live in COLD climates is a must, but don't bother once it starts warming up.


Regards,

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Dave
Boise, ID
Check out my website photos, documents, and movies!

I agree about the fuel mix change for winter. Me, I let the car idle up about 15 mins in the morning to have at least a little power. When bone cold the 300d (turbo) just plain won't get out of its own way. The Power RS stuff I'm adding says on the jug, 96 ozs per 300 gals of fuel, so I guess it's aimed at truckers. I put in a tad over a half a cup per tankful. Being as this is my first winter with a diesel, I can't say if it really making any diff, I'm doing it for the gelling problem mostly because I get my fuel where I can't actually say if they do a lot of diesel or not because it's such a small place. Today's tankful checked out to 27 MPG, mostly hi-speed hi-way.

I used to put in 1 qt of ATF, and one gallon of 91 octane with a full tank of diesel in my car, and it increased the mpg by 1, and it was a lot quicker off the line and it started better. My friend said in norway, they do half diesel half gasoline, but I dont know about that, im kinda worried.

Now my mpg sucks, its like 21, but I live at 7000 feet going to school, and I let my car idle for about half hour a day, and I drive quite a bit in town.

I switched from 76 to sinclair diesel and it has helped a little, now I am getting 22mpg, but 17 inch wheels with michelin pilot sports doesnt help much. Studded tires are evern worse.

I think that I am going to add some 44k next tank to clear out the injectors, and then put in new fuel filters at the next oil change, and purge and clean the injectors again.

I think its the altitude, and the engine tired of turning my wheels, and tired in general.

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Current Stable:
1994 S500 v140, 210k miles, white with grey.

Former Mercedes in the Stable:
1983 300CD Turbo diesel 515k mi sold (rumor has it, that it has 750k miles on it now)
1984 300CD Turbo Diesel 150 k mi sold
1982 300D Turbo Diesel 225 sold
1987 300D Turbo Diesel 255k mi sold
1988 300 CE AMG Hammer 15k mi sold
1986 "300E" Amg Hammer 88k mi sold (it was really a 200, not even an E (124.020)
1992 500E 156k mi sold
etc.