To help on cold starts (my thermostart is dead):
1) Change to full synthetic oil in crankcase because thin oil lets engine crank faster
2) Block heater in lower radiator hose, plugged in for several hours before cranking, warm thin oil lets engine crank faster. The electric, oil-filled radiator under the tractor, under a tarp sounds like a good idea.
3) Trickle charge battery night before, charging warms the battery a little, higher voltage helps it crank faster. Clean terminals at both ends of positive and negative cables.
4) Use decompression lever, because it lets the engine crank faster. Read Yanmar owner's manual for procedure.
5) Use powerservice fuel additive with antigel. Set throttle to maximum to start, reduce to half as soon as engine catches.
6) Get a hair dryer (yard sale or Walmart. not your wife's). Remove entire air cleaner assembly. Run hot air into intake to warm intake and for engine to suck warm air when cranking. Hold hair dryer on intake while cranking and until engine catches, you need an assistant for this. Hair dryer running and starting fluid is explosive fire hazard.
8) Ether was an extreme solvent, starting fluid is too, but not as bad. Solvent is not what you want on your cylinder walls. WD40 might be a good substitute.
9) After cranking the engine (decompression with left hand)to get lube and fuel moving, I use ONE short squirt of starting fluid, sprayed at the intake with my left hand, WHILE the engine is cranking. You can hear the engine suddenly rev up from combustion of the start fluid (that is abusing a cold engine.) Do not ever spray start fluid into a engine , then crank it, that is how to break something.
10) On a cold morning, begin early on these procedures, be patient, there is no good, quick way to start a worn, older diesel engine. Hurrying or using shortcuts may cause you to damage your tractor.