(perhaps this test has already been posted - I didn't see it in looking at a couple of pages of this particular forum) So I'm reading the latest edition of "Action News" - an Amsoil pub. Given to me by my friend who is an Ams. rep. Amsoil has a full write-up of a test they did in garbage trucks used by a company in Minnesota - these particular trucks are very abusive of the oil in that the oil is tasked in the engine as well as the other machinations of the trucks including one requiring 3500 psi on the oil. Long story short - the trucks were run on Rotella 15w40 for around 240 hours, then run on Amsoil for close to 1000 hours. Rotella got slaughtered in the testing - viscosity plunged, TBN plunged, all in 240 hours. Amsoil, for the duration of the sub. 1000 hour, pretty much held steady in visc. and TBN. One of the engines was torn down and measured for tolerances after the Amsoil run. Results were excellent except for one ring they believed may have been defective from the start - since all others were within new tolerances. My broodings here are not so much on Amsoil's performance, as it is which product Amsoil chose to challenge. I'm not starting the argument on "they should've tested against Rotella T". I'm making the pt, that if Amsoil is going to run this test, then they are likely fairly confident before hand that they will spank the competition. Thus my pt is, what does this say about Rotella 15w40. Amsoil chose that product, and that product fell apart in visc. and TBN (and in short order). Not a confidence builder in Rotella 15w40 (imo).