I would be interested in the results with 15ppm diesel
There's a couple of things wrong with your assumptions. You get 20MPG with raw fuel. That's great, but I get 16MPG. Let's do the math here.
Cost of Stanadyne per gallon treated is $0. 08, so to treat 30 gallons (a tank full) the cost is $2. 40
If my truck gives me 16MPG untreated, then a 30 gal tank allows me to drive 480 miles.
If fuel costs $4. 80/gallon, then a tank (480miles) costs me $144. 00 or
---> To drive 1 mile it costs me $0. 30 [untreated]
Now, let's add the Stanadyne. $144. 00 + $2. 40 = $146. 40 (this is what it costs me to fill up and add the Stanadyne)
Now I get a mileage of 16. 63MPG which allows me to drive 498. 9 miles (18. 9 more miles on a tank)
A gallon of treated fuel costs me $4. 88
498. 9 divided by the cost of a treated tank $146. 40 = $0. 2934
---> To drive 1 mile it costs me $0. 2934 [treated]
Or in other words I can go 18. 9 miles more on a treated tank of fuel. To drive that 18. 9 miles on untreated fuel it would cost me $5. 67. So there in lies the savings.
Not a big deal, but if you drive 12,000 miles in a year (at today's prices) the cost of untreated fuel would be $3,600.
On treated fuel the cost to go that same 12,000 miles would be $3520. 80, a $79. 20 savings.
And this says nothing about the added benefits of the lubricity and longevity of the fuel system.
I have doubled up on the additive and I did get better mileage than at the normal rate, but that does not necessarily mean that adding more is infinite. You can't add a full tank of stanadyne alone and get phenomenal mileage. It just doesn't not work that way. I feel that it is safe to add up to 2 times the recommended dose, but I wouldn't add more than that.
BTW, most of our customers report better mileage gains than what I get with the stanadyne. I'd like to hear some reports on what you all are getting. My test was back when fuel cost 1. 79/gal. About 5 years ago. I haven't done a test lately for an up to date comparison.