Originally Posted By: BigCahuna
Harley motors are considered a looser fit motor compared to other brands. Unlike water cooled motor which run at constant temps, Harley's cooling is dependant on air temp. And being looser, it allows it to expand as much as it needs to. The rear cylinder also tends to run hotter due to placement behind the front cylinder. I've had 2 Harley ultra classics, one was a '93 Evo motor and the other was a '03 twin cam motor. With the Evo,motor heat was something I never gave a thought to, but the twin cam had me checking to see if it was on fire several times. And the 20/50 wt Amsoil I ran in it, would drain faster then water. After seeing that first hand, the thought of running a 15/40 wt oil never entered my head. I actually was thinking about using a straight 60 wt like what hey recommend in the manual,But sold the bike before I got to that point.,,
Your entire statement is right on. I've noticed the same heat issues going from the EVO to Twin Cams. I personally refuse to use HArley's SYN3 as it is an overpriced and under performing oil compared to what else is on the market. I also stick with 20W/50 oils, however I did run 20W/60 Redline MC oil once. I used to use Mobil 1 V-Twin but now use Redline 20W/50 MC oil. NOthing wrong with M1 (still use it in my wifes lowrider) I just buy the Redline powerpack which has all the fluids for the bike in a kit.