I've run my B2650 for hours at a time in -25 to -30°F actual outdoor temps. But that's after I first bought the tractor and found out it couldn't even warm itself up in those temps without some help in the form of winterfront covers. That led to my making the winterfront kits that fit a few different Kubota tractors.
The cardboard insert in the radiator did help a little, but that still leaves the hydraulic oil cooler out front in the cold. In those same cold temps, it also didn't keep the engine compartment itself warm. When it was -25°F with just a radiator insert in the screen location, my hydraulic oil started to thicken enough that I couldn't maintain rated PTO rpm for the snow blower (standing still with no snow loading).
The full winterfront kit solved all those problems....quick warm ups, nice normal engine temps, warm hydraulic oil/transmission, warm engine compartment and fuel, and no snow ingestion into the front air intake nozzle.
Here's a link to the
B2601 Winterfront Kit with some pics and info.
If interested or have any questions.....just ask....or start a conversation.
We may not be in Alberta, but we're not too far from it.....or it's cold temps at times!
David