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Raw Water Cooled VS. Closed Cooling Life Expectancy...-gctid350550

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    Raw Water Cooled VS. Closed Cooling Life Expectancy...-gctid350550

    In looking at boats I'm confronted with the idea of getting a raw water cooled engine. The few I've looked at have either 100 or 400 hours on them of fresh water use only. I'm going to be only on Salt Water and wondered how long I might expect these blocks to last. One is a big block and the other a 350.

    I guess I could add closed cooling if it was affordable, but let's leave that out of the equation for now.


    I'd remove the T-stat housing and have a look, and see what kind of corrosion you find in there.

    If it's been cared for it can be pretty clean in there and you can bolt on a closed system and go.

    I used to work for an exchanger place and got to see alot of engine parts......remains would be more correct....that were ran raw water cooled and it's amazing how fast cooling passages fill up with rust scale in salt water. Head bolts get rusted and break off, nothing good happens and often the castings aren't even salvagable for cores.

    I would never run a raw water cooled engine in the salt, even if it meant the boat sat out a season while I gathered money for the cooling system.


      What Ryan said. I would also add that since you are planning to use the boat exclusively in salt water, I would not even consider an open cooling system. I have seen what salt water does to blocks with open cooling; and you definitely don't want to go there.

      Since we are in a buyers market for boats, you have the option of being picky. There are tons of boats with closed cooling systems installed. Save yourself the headache and get one with a closed system in there. The system will run under a boat buck for a 5.7, but installing it is going to take some time..and you'll need to evaluate whether you want to put that time in yourself (and miss out on enjoying the boat) or pay a marine mechanic to do it.


        Unless you flush the engine after each use I would install a closed system.

        Well worth the $1,000 if you boat in salt water if ask me.
        Phil, Vicky, Ashleigh & Sydney
        1998 3055 Ciera
        (yes, a 1998)
        Previous boat: 1993 3055
        Dream boat: 70' Azimut or Astondoa 72
        Sea Doo XP
        Sea Doo GTI SE
        Life is short. Boats are cool.
        The family that plays together stays together.
        Vice Commodore: Bellevue Yacht Club


          The scary part is, the engine will run fine unloaded or on the trailer, and look fine..maybe even very clean on the outside. But the inside can be full of rust scale and the whole engine can be junk because of it.

          I looked at, and passed on, a boat I was considering buying that had done 8 years in the salt with an open system. After seeing what was in one of the risers, I offered the seller a low price which offended him, and I basically told him that's what it's worth because I have to figure the longblock and manifolds are all garbage and I'll need to R&R.

          He didn't take the offer of course, and probably sold the boat to some unsuspecting and less enlightened person who likely had an unhappy experience the first time they tried to use it...

          Now if you can come upon such a situation and get the seller to come down alot to compensate for a needed new engine and manifolds, I'd go for it. Some will do it, and then you have a known new engine and hopefully alot less problems.


            The difference in corrosion between fresh water and salt water is simply astounding to those of us who never see the ocean. On BOC posts, I notice it most when there are photos of engine compartments. Things that salt water boaters don't notice include corrosion not only on the engine block and manifolds, but also on simple hose clamps, wires, battery connections and so on.

            My best friend bought a salt water boat from Florida. To get to the outdrive gears, we cut the cases in half with a grinder because they were so badly corroded.
            2007 Discovery 246
            300mpi BIII
            Welcome island Lake Superior


              I think that Mike is after info regarding the life expectancy of a raw water cooled engine.... and then adding salt water to the equation.

              Raw Water Cooled VS. Closed Cooling Life Expectancy...

              I believe that he's looking at a few boats that are open system cooled, and he'll be running in brackish to full salt water.

              Rick E. (aka RicardoMarine) Gresham, Oregon
              2850 Bounty Sedan Flybridge model
              Twin 280 HP 5.7's w/ Closed Cooling
              Volvo Penta DuoProp Drives
              Kohler 4 CZ Gen Set

              Please, no PMs. Ask your questions on forum.


                With a used boat with raw water cooling, you will never know if the engine was flushed after every use, and unless you remove parts you will not know the amount of corrosion and rust inside. Removing the thermostat housing is one way to check, another is to run the engine if out of the water with a hose attackment and watch for rusty water exhausting.

                I have seen a few raw water cooled engines, rust-rust and more rust inside.
                Pat says: DO-IT-RIGHT THE FIRST TIME!

                Bayliner 3870 "ALASKA33)
                Twin 350 GM power
                Located in Seward, AK
                Retired marine surveyor


                  I have seen many boats out there that are raw water cooled that are 15 to 20 years old and run fine. They do need more maintenance on the manifolds though. My friend has a Parker with a 454 and raw water cooled. he bought it 3 years ago and it was from Florida. It has 1800 hours on the mill and has no issues. From what I read, the rule of thumb for longevity on raw water cooled is approx 2500 hours. to me, it would not be a deal breaker. I would continue with the raw water cooling until I was ready to repower. Sadly, when I did repower a few years ago, I did not go closed cooling. :livid: Still on the same set of manifolds, but i do wished I had converted when I repowered.
                  Tony, Cape Cod, MA
                  Vice Commodore Bourne Yacht Club
                  1994 Carver 390 Cockpit Motor Yacht
                  454 Merc Cruisers inboards
                  2014 10' hard bottomed Dink powered by 3.3HP Mariner 2 stroke


                    My '05, 305, was in Salt Water for almost 5 years (raw water cooled) before I sold it, about 250 hours on it in that time. Regular maintance included changing the impellers & thermostats twice. Pulled Port engine manifolds to inspect in '09 and they looked good. I would spray WD40 on things like carb linkage, shift cables, etc. Just hardware that made common sense to coat. Hose clamps all looked good. So from an engine standpoint, nothing really unexpected to see. Even when we pulled it yearly for lower unit oil changes, checking bottom paint, thru-hulls, etc. nothing unusual. Bottom paint would go 18 - 24 months. I have friends in the same Marina that have had their boats in at least 10 years or more. Still running strong with regular maintance. No engines replaced. Several have had their manifolds and risers replaced. No failures, just preventitive maintenance.

                    The only thing that drove me nuts, was having to replace the Zincs every 4 - 6 weeks. I had the bottom cleaned every 3 weeks, and it litterly seemed like every other time or so, the diver was replacing them. In our marina (Newport Beach), they place the old Zincs on your finger, so you can see their condition. I never did figure out if we were getting (what I thought was) too fast of wear from other boats around us or what. But it sure added up in the "monthly" expenses keeping it in the water full time.


                      something else to consider...If kept in the water, corosion in salt is worse because salt water conducts electricity better than fresh. On raw water systems, this electrolisis corrosion is inside the engine along witht the corrosion from the salt itself. I have seen trailered cruisers regularly used in salt, raw cooled, and flushed religiously last 20 years. The engine wore out before it coroded. then on the engine replacement, the manifolds were re-used because they were in pretty good shape.

                      Fresh water cooling with antifreeze is bar far the best, but if raw water cooled, flush, flush, flush...