Are you done boating for the year? If so, you need to winterize it, or have someone do it for you. If you are still using it, drain the block after use.
If an outboard, open the thermostat housing, tilt the engine and pour recreational antifreeze through the engine until it comes out the exhaust. Rotate engine back up and let drain (into bucket hopefully). Next, if possible, spray fogging oil into carbs while rotating engine. Spray bare metal with WD40 or LPS and cover.
This has worked for me for many years and I never cracked a block. At the end of the season, I used to run my carbs dry on the engines that weren't F/I.
Sorry...meant to post more info but got busy. It is an i/o Volvo Penta 5.0. I plan on fishing probably until the end of the month so no I'm not done using it.
I've never worried about it until after Thanksgiving (I/O,outboard etc.) since the chances of it staying below freezing 24/7 for more than a day or 2 are slim.
A guy at one of my accounts says he puts a drop light down there on the cold nights until he is ready to winterize. I wouldn't think it would put out that much heat but he says it works for him.
In the water or on the trailer? If on the trailer/lift and you want the best temporary protection: put a hose bib on a 2 gallon bucket or jug and mix up a 20% solution of propylene glycol. Buy one of the $5 short hoses from the depot. Connect your glycol jug to a set of flush muffs and run the engine for a few minutes after each use. This will fill everything with enough antifreeze to keep the system good until the next use. Up the ratio for winter storage.
I had an IO for 8 years
Mine was a mercruiser and it had a pump attachment that blew most of the water out of the engine. I was told I could use that to run all year. See if you have it.
Make sure you are careful about powering anything in the bilge you don’t want any leaks with fumes causing a fire