Closed loop cooling with a heat exchanger and antifreeze is always prefered to raw water open cooling on any engine.
The only downside to closed cooling is the initial expense. So you do want to weigh your options.
With direct raw water cooling, engine blocks will eventually rot out over time. Once the block is rotten, the only choice is to replace the block or scrap the PWC (depending on what is more cost effective for you).
But you also want to be realistic about that initial expense.
If you are only going to jetski in freshwater lakes, and the occasional trip to saltwater just a few times a year, the actual blocks will last near forever. Much longer than the rest of the jetski.
But if you jetski primarily in saltwater, and saltwater only. Even with flushing the engine every time you your looking at 8 to 10 years tops out of the engine block before it is rotten to the core, and requires replacement.
I am in SW Florida, on the gulf. Some of the saltiest water there is. If you never flush the engine after saltwater use you are looking at 4 or 5 years tops, and then the engine is rotted.
So you have to weigh out the initial expense of the closed cooling. If you only jetski in freshwater, that is kind of a no brainer, you do not really need it. But if you are jetsking in salt, it does make a difference.
Now in freshwater only, the block will still eventually rot out, but you are looking at 15 to 20 years of use. Something will more than likely break before the actual block rots out.
The only other benefit to closed cooling is that does allow the engines to run a bit hotter. And a hotter running engine will get a slight bit better fuel economy. But again, realistically when it comes to jetskis/PWC's. Economy usually is not the primary concern as they run at full throttle most of the time.
That about sums it up. I do work for tips so if there is something you need more clarifaction on, or have further questions about, by all means just ask. I do want to make sure you are 110% happy with me. If for some reason the website does not let you rate me, and get some kind of error. If you could let me know that would be great.
Not at all. Saltwater is the biggest killer of engine blocks. If the water is fresh, but even brackish or muddy, that will not change overall engine life. It is still a good idea to flush every engine on theclean freshwater garden hose after every run. But if you boat in freshwater, not doing that will not destroy the block from rot. But if you were to boat in saltwater, it would.