(Pretty) Prius Prime first world problems! :)

Unless you can warm up the engine for long enough periods, condensation can build up in the crankcase.

 

I'm about to mow mine now. With my Toro electric mulching mower that is going on probably 15 years. Somehow, I have no idea how, with the original battery. It's some exercise. Not really a lawn, whatever comes up. But it all gets mowed to one level.

To the OP: just get the electric mower, if you plan to keep mowing. So much better, quieter, easier. Gas mowers go on forever.