Zahn cup, or a homemade version of one. We used them in a printing plant to measure coating viscosity. It was round cylinder with a spherical bottom and a hole dead center to the bottom, held maybe 2 or three ounces. We would use a stopwatch and time the flow at a certain temperature to reach the required viscosity.
Take a 20 pop bottle drill a 1/8th hole in the lid, fill bottle with diesel, and time it to empty, be sure to poke a breather hole in the bottom of the bottle. I plan on doing the same thing so i can come up with a perfect winter and summer viscosity that I can shoot for. Be sure to find an easily obtainable temperature to make such measurements at. 75 degrees might be hard to get down to in hot summer, but is easily reachable with a little heat in winter. Or forget the temperature and shoot for the same drip time winter or summer and you'll know what will reliably flow at those temperatures which would be a better way to do it due to viscosity modifiers in lots of oil that make viscosity/temp react extremely non linear to temperature changes.
