I use 15w50 Mobil1. If I could get Mobil 1 5W50 I'd use that, but it's not available in my area. The reason for wanting the cold viscosity number to be as low as possible is that the oil has to get to where its needed on start-up, where most of engine damage occurs. Notice the little lines that run to the heads of your Vstar. The reason for the 50wt oil at operating temp is the amount of weight being transferred by the large pistons. In an engine the bearings are not supposed to touch surfaces. The oil provides the cushion that keeps these tight tolerances apart. As the engine gets hotter it gets easier to squeeze this cushion out. So an oil with a higher viscosity at operating temps works better. The reason its hard to find oil with these wide ranging viscosities is that for the most part it's done through additives (polymer chains) that shear away as the oil gets used.
2005 1100 Custom
ORKed 5/16" Lines
PODs K&N RU-600s W/PCV
PCS XXX/2 cams
Jetted & PMS Tweaked 20.0/152.5 3.0 turns
Wimmer Machine Custom Oil Cooler & Stash Tube
Dyna 3000 Step 5/ 6500 redline
6" Fwd Control Extension W/Boards F&R
Memphis Shades Bullet Fairing
Progressive 465 rear
Progressive Springs and GVE front
10,000 Monkeys throwing crap at the glass and this one thinks he's Picasso...
Last edited by Fulltilt1; 02-07-2011 at 08:39 PM.