Second the prior poster wrt using a lower radiator hose heater.
The best I've found and what we use (several around the place) is Kats by Five Star Manufacturing. Looks like a red 'T': you cut the lower hose and install it using supplied hose clamps; the leg of the 'T' is the heater element, much like a miniature home water heater.
Works like a charm. Had one unit fail and 5-Star sent a replacement no charge.
Bundle the cord and restrain to the machine with a cable tie so it doesn't drag the ground or snag something while the tractor is being used.
Others brands and models exist. O'Reilly's will cross a part number to come up with a silver aluminum clump looks like a softball with two ports. Poorly made and lower heat output than Kats.
We run ours at least 2-hrs in a closed shed (no wind sucking heat from the cast iron block) when planning a start under 40F. Can use a timer too. If planning to move early we just leave it plugged in overnight sometimes. We're conservative in how we treat our engine; others may argue no need to preheat even below freezing.
Your glowplugs cycle based on a sensor reading coolant temp. At -10F after heating our gp's cycle 'on-off' in about one second and the tractors will light fast and easy.
For cold weather also consider installing an onboard battery maintainer trickle charger, such as Schumacher. Avoid Harbor Freight as junk. Cold weather starts with warm engine and full battery are never a problem.
Pulled oil pan from old Ford PU and found where magnetic sticky heater had burned a ring of crusty oil inside the pan. Never had any luck with dipstick heaters as not enough heat output and heat didn't travel up into block before start, same as magnetic.
One thing: to make getting the heater out without damaging the hose (someday the heater may fail before the hose does, someday, any such heater) smear the hose ends of the Kats red 'T' with a dab of plumbers silicone waterproof grease--sometimes called stem grease. Just be sure it's silicone, not hydrocarbon-base 'grease'. I give a buck for a tablespoon full in little flip-top pillbox container and it's almost a lifetime supply. Also good for lightbulb bases especially in outdoor sockets.
Please post back how your proceed so we may all learn.
