Yesterday I started my JD D140 lawn tractor at 28 degrees F with RT6 15w-40 in the sump. It turned over very slowly, but fired up on the third try. Our overnight tempertature was 16 F, so I will venture a guess that the oil was actually cooler than 28 F. In any event, the machine started and ran at a temperature where I would never expect to use it. 15w-40 Rotella T6 will remain as my go to OPE oil for machines that run at or above freezing. That is everything except the snow blower. I may go off the reservation next spring and start putting the same oil in the Honda powered machines that currently run on 10w-30 M1 HM.
I have two machines that take some muscle to start. One is a Billy Goat leaf vacuum with a Honda GSV190. The other is a Predator chipper / shreader with the Predator 212 cc engine. In both cases it is the heavy rotating parts that make them hard to pull start. If any of you have gone to thicker oils on machines such as these I would sure like to hear about it.