An older 80s anything running on propane is likely to run poorly at temperatures close to 0 F degrees. In fact, a lot of newer propane fueled stuff does not always enjoy good operation at those temps until the engine is warmed up well.
And on that note, it would be a good idea to know that the engine thermostat was functioning properly.
Just last week one of our older Komatsu Dash 12s (Impco J reg and VFF30 lockoff) would not run satisfactorily.
Noticed the temp gauge showed cold.
Checked gauge and it was working. Found thermostat was staying open about 1/16" and that was enough to keep the coolant chilled in the 10 F degree weather we had then.