I don't think the viscosity has anything to do with performance unless it’s so thick it can’t be pumped. Sure, to reduce pumping loss, I can imagine in a lab of some sort you could measure the amount of difference it takes for a thicker vs. thinner fuel. But I don't think there is an optimum viscosity. Viscosity doesn’t make power, or reduce it to the point where it’s going to affect mileage.
In fuels, the things that are going to make a difference are the heat index (mentioned above) more specifically the amount of energy that fuel contains. WVO/Bio-diesel has a higher amount of BTU than straight diesel. The difference in the energy content and burn characteristics of the engine is what makes the difference in power and mileage, not the viscosity.
Ferroequinologist was pointing out how to measure the viscosity of your WVO (or whatever) so that you know how much to mix with diesel. I'll put it an easier way to look at it... think about it like making pudding or some other sort of food. Too much of one thing makes it runny, too little and it’s too thick. That’s what he was describing, how to measure your waste fuel and cut it with diesel. (BTW I used to test fuel in the navy too, small world)
In a modern diesel, it is going to be more important to maintain a thinner viscosity due to the sensitivity of those engines. In the deuce, it’s not so important.
(NOTE: For clarity, I've removed the portions of the above post regarding Veggie Oil).
I know that a given amount of a "fuel" will yield an (x) amount of BTU's or calories in an engine.
But, I made an observation with my truck recently that set me thinking and searching the threads about this:
My last tankful of Waste Motor Oil & Diesel was about 90% filtered WMO mixed with 10% diesel.
I noticed that the truck had dropped in power going up and down the hills and was smoking a bit more.
When the tank was about 1/2 full ... I stopped and pumped in TWO gallons of diesel.
The change was dramatic and almost instantaneous. All the power was restored and the smoke cleared up ...
OK ... so that set me to thinking ...
What had changed?
Its got to be that the 2 gallons of diesel I pumped in:
a) improved or added BTU or calories to the WMO in the tank
OR
b) it lowered the viscosity to the point where the fuel flowed through the system (pumps and filters) better.
OR c) something I'm not considering.
anyoldways ...
just for the sake of measuring ... I'm going to take a sample of the fuel in my tank, a sample from the batch of WMO I got in storage ... and a sample of fresh diesel ... and do a couple of measurements with a viscometer and a hydrometer ... for comparisons. It don't cost anything ... and I got a little time.
Also, because my driving cycle back and forth to school is so widely varied (I do almost exactly 100 miles per day. A pretty even mix of NoGa hills, 4 lane highway, and a bit of stop and go driving in Marietta) I get a real good MPG & Power test.
I've also become friendly with one of the Instructors in the diesel program where I go to school and see what he thinks.
all thoughts welcome
oddshot