From my 82 year old dad who farmed his entire life and had 3100, 3600, and 3800's back when they were new....he used it for all 3 reasons. Helping to keep a cold engine running on start up, PTO drive off the tranny, and yes..the high tech cruise control! He was also a mechanic his entire life on the 'outside world' to supplement the farm income. He has been a huge help in my restoration of my 49' 3600. Helps to have first hand working knowledge! Mine was missing parts and pieces and he remembers where everything goes and can describe in detail what used to be here or there and how it hooked up.
