Hey bonjo, The reference is to both 10W40 and 15W50 vs 20w50. I ran 10W40 for about 1000 miles after I installed new pistons this past January. Granted, temps here in Colorado where I live and ride don't really get above 70° on a consistent basis until late May/earlyJune, but I had some rides where temps were in the 70's and no fan at low speeds and in traffic. But again the "cooler" temperatures could have contributed to that. Then fast forward to the past two weekends...
The past two weekends I have gone on rides where temperatures are in the mid-80s and stuck in stop and go traffic coming down out of the mountains on Highway 24 from Woodland Park into Colorado Springs. Stop and go at higher elevations is even tougher on engine cooling because of the thin air. Not as much relative air to flow over the radiator even at low speed. The fan did not come on with the 15W50 Mystic JT8. Last year even with temperatures in the low 80s, the fan was coming on fairly consistently with 20W50 in the same conditions.
The only caveat is in January I completely drained then refilled and bled the cooling system when I put in the new pistons. Potentially there could have been an air bubble in the system last year that I somehow did not get out when I bled it last spring when I put in new coolant. The ZRX is known to be sensitive to an air bubble getting trapped in the system and causing mysterious fan running. Since I didn't do anything different in bleeding the system last year vs this January, I doubt it was a bubble, but I felt I needed to share that.
The past two weekends I have gone on rides where temperatures are in the mid-80s and stuck in stop and go traffic coming down out of the mountains on Highway 24 from Woodland Park into Colorado Springs. Stop and go at higher elevations is even tougher on engine cooling because of the thin air. Not as much relative air to flow over the radiator even at low speed. The fan did not come on with the 15W50 Mystic JT8. Last year even with temperatures in the low 80s, the fan was coming on fairly consistently with 20W50 in the same conditions.
The only caveat is in January I completely drained then refilled and bled the cooling system when I put in the new pistons. Potentially there could have been an air bubble in the system last year that I somehow did not get out when I bled it last spring when I put in new coolant. The ZRX is known to be sensitive to an air bubble getting trapped in the system and causing mysterious fan running. Since I didn't do anything different in bleeding the system last year vs this January, I doubt it was a bubble, but I felt I needed to share that.
