Agreed Hohn, the variations in some areas can be extreme but if each driver follows their normal routine we should be able to see if the product makes enough difference to produce a statistically significant result.
Rationale: If you keep track of your mileage under similar conditions, many of the items mentioned will be 2nd order effects, the really critical ones for mpg are similar driving conditions and technique (speed, amount of hotrodding, etc). For instance, air entrapment in the fuel is an evil that is present regardless of additives, yet those who track their fuel usage can observe remarkably consistent results from these very efficient diesel engines - without air entrapment it might be a couple of gallons better, but the foaming action at the various pumps and its impact on mpg must be reasonably consistent or we would see some significant variations in mpg from fillup to fillup.
As far as cleaning the additive out between measurements, we could always do 2 fillups of plain diesel with tank down to a couple of gallons at fillup, although I suspect one fillup is actually "good enough". The dilution is pretty rapid, for instance if you had a 32 gallon tank of diesel with 16 oz Stanadyne, and filled up with only 4 gallons left in the tank, you would have 2 oz of Stanadyne distributed through 32 gallons of diesel fuel. Repeating this on a 2nd clean tank, you would have 1/4 oz Stanadyne in 32 gallons. If Stanadyne effects the readings at such low concentrations in a statistically signficant manner, I will buy a case of it right now because I haven't seen much effect so far at the recommended dosages
One of the interesting things about the Cummins engine is its efficiency and consistency in these trucks. Going back and forth to work and driving around unloaded, my truck will return about 20 mpg day in, day out with a standard deviation of only 0. 8 mpg. I track our other vehicles the same way, my wife's Honda Odyssey has an SD of 5 mpg, the mileage can vary significantly. Our old Suburban and my previous truck had results not much better. The CTD on the other hand, is very consistent. That's why I think we would see if any of these products provide a statistically significant improvement in mpg.
Flatly put, if the products don't provide a statistically significant improvement, they aren't worth buying on the basis of improved power / mpg, only the anti-gel and lubricity properties would be of importance to the average driver. It would be interesting to test those as well. Anybody up for the "jug of diesel in the deep freeze" routine?
