Diesel oil change question

[Sterling]

Frank,
Are you talking about seeing internal rust problems after a winter layup...like a few months, or are you talking a few years on blocks, multi seasons, etc for rust problems?

[seapower]

Both actually. If the life of the oil has run it's course, the additive's that are put in the oil are worn out or gone in some cases. After oil has been used for sometime it loses it's "newness" so to speak, that's why you'll see increased oil usage after the oil has run it's course. Old oil just doesn't coat and adhere to surfaces like new oil, it run's off quicker. The length of time an engine sit's up does matter. Think about this, every time you have condition's that create condensation, water droplet's form right? As those droplet's run down or hang's around some oil goes with it. Oil float's to the top does it not??? I have seen some brand's be affected more than other's.
On the same topic. If you have water in the oil, "boiling" it out using the oil as a heating agent isn't alway's a good idea either. Oil will generally run approx 20 degree's hotter (just a rule of thumb), than your coolant. Depending on how hot it actually get's will effect the way the water "disappear's". If it is hot enough (warm) to let the water evaporate that's one thing. If it run's hot enough to boil the water out, that is another situation all together. If the water boil's (from actual heat or from friction) on the bearing surfaces, guess what it takes bearing material with it. Boiling is a violent action, many have learned this the hard way.
Again no arguement here, not trying to push anything. Just reporting what I've seen in the few week's I've been doing this. Frank,SeaPower

[megabite]

Change your oil with Shell Rotilla or Mobile 1 synthetic oil every 150 hours.Start your motors twice a week.Keep your block heaters on to prevent moisture.Use a dehumidifier or a radiant heater in your engine room.You also need to treat your fuel tanks so bacteria wont grow in your fuel while the boat sits.Dirty oil kills Turbo chargers !!!!