Bob
Maybe rtsdad is correct BUT just because I asked for FACTS that the next lighter weight engine oil causes engine to start 60%-80% faster & he supplies no real facts BUT instead supplies a SMOKE SCREEN MAKES ME WONDER.
I can't give you "facts" per say but.
My Branson 8050 with the power shuttle trans would not start in below zero F temps.
The starter would crank the engine over about a half of a revolution and just stop, booster packs, jumpers all made no difference.
The only way that tractor would start on below0F days was to put the salamander heater right up behind it with a tarp on the hood going to the ground
as a tent. After an hour she would start fine.
I did two things at once so who is to say which was the most important.
I removed the factory hydraulic/transmission fluid and filled it with Cen-Pe-Co multi purpose fluid.
I drained the engine oil and replaced it with T6 5W-40. After these changes she started fine the oil pressure light goes out quicker.
This was 6 years ago and to this day she is running on those types and brands of fluids.
It cranks over much easier and faster and has done so since they were installed.
I also use the T6 5W-40 in my IH574, and Kubota F2000, and even in my small engines.
I also used it in my RAM Eco-Diesel PU.