Before we can answer that, we need to know how the water got in there.
You drove into water too deep for the rig?
A flood in your neighborhood?
You accidentally put water in the oil cap when adding water to the windshield washer tank?
You have a blown head gasket?
Is water going to get into it again?
If you haven't exposed the engine to water, the most likely culprit is head gasket. Is your radiator low? Is the antifreeze the proper color? Is there foam in the radiator? As Rik stated, the more information you can give, the better we can help to diagnose the problem. As far as treatment, there is no treatment that I have heard of that can help. You must find the root of the problem and fix it.
If let's say it was a head gasket (that was repaired) or a swamped engine,....
If you really want to get it clean....
Drain all the oil and remove the oil filter. Let it sit for at least a day with the drain plug out.
Put the drain plug back in and replace the oil filter with a cheapy one.
Next pour one gallon of kerosene into the oil filler cap.Let sit for a few hours, then start the engine and let it run for about one to two minutes, no more.
Drain the engine again and let it sit for a few hours without the plug or the filter.
Put another cheapy filter on and replace the plug, put a detergent oil in like Mobil One and drive it for a few days. Change the oil again including the filter but this time use a good filter.
You should be fine after that.
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