How often to start the engines?

Under load is a very different thing then idle. Sitting winterized or just sitting after an oil/filter change is a very different thing than sitting with used oil (acids in it) .
Was told for engine life (natural aspiration or common) change oil/filters before long periods of non use. Periodically run at at least 80% load for awhile to make sure everything is in order. With N/A more important to burn off carbon. Told not an issue with common rail which may do better if sitting for a long time.
Had a Cape Dory 25 on a mooring. I could sail off/on the mooring so one season didn’t run the engine the whole season. When in the fall it came it was time to use the diesel engine to get to the hydraulic trawler to get to my yard. It over heated. I could run it briefly then stop to cool and then had it pulled in to get it on the trailer. Taking a look see there was hard growth including shell fish in the cooling system. No active growth inside ( no light or oxygen.)
Same reason when ever I’m on the current boat while tied up I run my thrusters. Just getting them to spin helps get growth off them to my logic. Water does puddle in spots internally when a boat isn’t run for a long time. Maybe less if you close intake and exhaust through hulls. To my thinking running it briefly under load to run water through the cooling system may help the anodes do their job. Never heard of confirmation of my thinking but several old salts told me. Change oil before letting it sit. Run it hard occasionally if sitting in the water for long times. Good to spin the shaft, prop and tranny as well for growth and prevention of oxygen starvation.

Guess no one here has engine oil analysis from before docking and after sitting at the dock and starting the engines once in a while

I wonder how the fuel in the oil results change

Hippocampus said:

Sitting winterized or just sitting after an oil/filter change is a very different thing than sitting with used oil (acids in it) .

Click to expand...

I continue to be amazed at how often I see this reasoning.
Lube additives include a base that neutralizes acids. Lube analysis includes measuring the level of TBN ( Total Base Number) which indicates how close the additive is to no longer being effective at neutralizing acids.

Also... for the how often to run question...
even if the oil is slightly acidic is it better to run it frequently and distribute through the engine or leave it sit and have it drain down leaving little in the engine and more in the pan??? Short runs and runs w/o load run more risk of building up moisture and products of combustion in oil IMO

I believe that if sampling & reliable analysis is good enough for managing oil changes on OTR truck fleets... its good enough for me & my diesel maintenance. These guys are generally shooting for 1 million miles between rebuilds.