I was away and did not get to the boat in time to turn the cabin heater up before our cold snap two nights ago. The low for the night was 16 degrees and I only had the heat on 500 watts
I got down yesterday and checked, the engine got down to 33. That was CLOSE, even if our water probably has to be about 29 to freeze. I just couldn't resist starting her up to make sure all was well, which it was.
Cold engine and about 2 minutes after starting shown.