Actually, a 5% increase in fuel economy will save me almost $0.94 every time I fill the tank.

Calculations based on: 23.5 mpg base milage (average recorded milage over the last 3000 miles)

with a 5% increase = 1.175 mpg (or 24.675 mpg total)

average cost of D2 over the last 3000 miles = $2.91 per gallon

I averaged 332 miles between fill ups (over the last 3000).

When I use DK, I add 12 oz DK at every fill up at a cost of $1.25. (I bought a 96 oz jug of DK at Wal-Mart for 11.96).

So:

A 5% increase in milage saves me 0.673 gallons of D2 at each fill up (13.455 gal vs 14.128 gal), plus adding 12 oz of DK replaces 0.078 gallons of D2. That equals $2.18 worth of D2 saved for every $1.25 worth of DK spent.

Now, lets turn the calculation around. How much of a mpg increase do I need to see before using DK is no more expensive than not using it?

First 12 oz of DK, replaces $0.227 worth of D2.

Therefore, adding 12 oz of DK only increases the cost of a fill up by $1.023.

At 23.5 mpg, I use 14.1276 gallons of fuel at every fill up (332 miles).

To make up the added cost of DK, I need to use 0.3516 gallons less D2 over 332 miles.

This means I need to get 24.1 mpg, or a 2.6% increase in fuel economy.

Provided that the product does no harm, you have very little to lose (or gain) by using it.

If there is little gain, why bother buying something, pouring it out, hoping not to spill the bottle, storage in the vehicle without spilling, etc, etc? For a fleet, maybe it might translate to some savings.

I'm just pointing out that the cost savings (for a w123 300TD) is negligible, if any. But at the same time, expense is negligible. You aren't going to spend much on it, and you definitely aren't going to save much by using it. So, forget the financial cost/benefit argument.

However, if it helps to clean 20+ year old injectors or cylinders over a few tankfuls, or if it helps to increase lubricity, or reduce emissions at all, then its a good thing (and a small price to pay).

If you want better fuel economy, make sure your tire pressures are good and slow down on the highway.

1976 300d 23 ~ 25 Mpg
 

I was hoping other 300D (114/115) owners could chime in on what their 300D MPG figures are.
Same for 123 300Turbo Diesel.
I know these are heavy cars, but if driven conservatively, with gradual accelleration from stand still I was hoping to hit in the high 20's.
thanks,
Rich

Bingo!
 

The little stickers with numbers on the pumps do NOT indicate a percentage. They indicate an anti knock or 'compressability' index. "Better living through chemistry" tells us - here in America - R+M/2 = octane rating.
R = research number IE: content by molecular weights.
M = motor number - fuel is is burned in a test bench engine, if I recall, according to ASTM specs. and the point just below 'knock' is found. Tetra ethyl lead, benzene even kerosene can add octane rating to gasoline without adding octane molecules. In Germany (if not the whole EU) only the research number is used.

I did a paper on 'organics in consumer contexts' in college and if I recall, cetane index is proportional to potential energy content per fuel volume at a specified temperature (I forgot that temp but I'll surf for it.)

ANYWAY having driven a truck, and seeing that 5% gain -vs up to 5%- I thought that would be a MAJOR REVOLUTIONARY breakthrough in transport costs. Think about how much 5% would translate to for ONE coast to coast trip! Some O/O truckers I've met swear by different additives and some don't.

My 240D (W123) has been seeing about 15 mpg (AWFUL!) for some reason, I've been adding half a bottle of DK to each tank I get. I buy the "Treats 100 Gallons for 3 Cetane Numbers", and am treating ~25 gallons with it, and it seems to smoke a bit less and have a bit more power.

Adjusting my valves, and cleaning/replacing injectors might get me up to the high 20s-low 30s, I should hope, but in the mean time...DK it is.

well played. well played.