Raw water cooled mercruiser moored in salt water

[Walker600]

Hey, Quick question, Looking for some non-biased non-salesman advise.
I have just bought a boat with a 5yr old raw water cooled mercruiser 3.0.
Up untill last year I belive it was always run in fresh water, But now it is running in salt water and I have no choice but to moor it at sea.
I have just ordered a replacement anode kit (drive, trim tab, trim choke, transom and propellor)
And now I am considering a fresh water cooling conversion (block only)
Do you guys think there is a big advanage to this or a properly maintained anode kit will be sufficent? I've seen a bit of conflicting advise but I can only think that it would not hurt to have it, but it's not cheap.

May thanks for any advise

 

[Aloysius]

Re: Raw water cooled mercruiser moored in salt water

Salt water oxidation and electrolysis are separate and unrelated. The anodes protect the sacrificial metals..the saltwater rusts the iron even with anodes.

 

[wire2]

Re: Raw water cooled mercruiser moored in salt water

It's my understanding that converting to closed cooling is most effective when it's done with a new (or almost new) engine.
Your block will rust with any raw cooling but there's lots of thickness.

The exhaust manifolds & risers are far more susceptable to failure from corrosion.

As mentioned, sacrificial anodes protect less noble metals in the water, a different process.
You might also want to look into a Mercathode system.

 

[JoLin]

Re: Raw water cooled mercruiser moored in salt water

Your motor is old to convert to FWC- the cooling system will clog with whatever rust and junk is already in there. Also, an aftermarket kit will typically FWC only the block- manifolds and risers will still be RWC and must still be replaced on a regular basis (5-8 years based on local mechanic advice).

In my area, few people seem to have FWC. There's a lot of plant life and critters (barnacles)to clog exchangers and coolers. It's something to consider.

Most of my friends are running boats with their original blocks, that are 20 years old and older.

There are 'flush' kits that you can buy or build, that'll let you flush the salt out of the motor after use, if you have access to fresh water at the dock (or will you be tied to a mooring buoy?). That would help and might ease your mind.

My .02

 

[Brentathon]

Re: Raw water cooled mercruiser moored in salt water

My first raw-water cooled 5.7 Merc lasted 16 years, without ever being flushed-out (between uses)....and the thing that killed it was seaweed clogging the drive intakes.
Blocks/heads can last 20+ years on saltwater.

 

[sasto]

Re: Raw water cooled mercruiser moored in salt water

You are doing the right thing by protecting your boat with anodes due to your location. Keep an eye on them and monitor them for awhile. Not much grows on you hull in those parts but a good ablative bottom paint is a must. Like the other guys said...I wouldn't worry too much about the saltwater and your cooling system....put your money elsewhere....like a good internal seastrainer. Enjoy the river cruises, Walker, I sure did. How long to you plan on keeping her at moor?

 

[Lou C]

Re: Raw water cooled mercruiser moored in salt water

Mine's 22 years old, at least half of that in salt, I do fill up the engine and manifolds with -100 when I winterize to cut down on corrosion...
If I ever re-power this boat (most likely will since it meets our needs without costing too much to run or store) it would be hard for me to run salt water through a nice new engine...So I think starting new I would put closed cooling on it...but as noted marine life can cause problems in heat exchangers and anywhere salt water sits...I even get barnacles in the water intakes in the drive and I break em up with a small screwdriver and then flush em out with a hose...
But I asked my mechanics about this once, and I thought they would be all for closed cooling, but they said you can have the engine 20 years and not have it rust through, especially if you fill it with the good AF in winter, and there is more to go wrong with closed cooling as well...

I would not put it on a used engine though. Flush it good at the end of the season, drain it and then manually fill with AF with corrosion inhibitors....that's the best you can do...

 

[Aloysius]

Re: Raw water cooled mercruiser moored in salt water

ford cast iron seems to hold up better in salt water than Chevy. I converted a 20 year old Ford to closed cooling, flushed the system with salt-away, and a few years later (last year) rebuilt the motors. tons of rust settled in the bottom of the water jackets, which I cleaned out. Old school trick, I put some oil in the coolant to seal the pores of the iron.

I've seen Chevys rust through in 10 years, especially the new lightweight castings.

 

[Walker600]

Re: Raw water cooled mercruiser moored in salt water

Thanks for the comments guys.
Im fairly sure its only had very ligt use in salt water for the past year, However now its facing the toughest time of is life....
Where I live doesn't have a winter, its hot all year round, so there won't be any winterising and leaving her stood on a hard gounding for 6 months of the year, and I guess short of me changing my boat she is destined to remain moored at sea for the rest of her life..... would this influence any of your decisions?

 

[Lou C]

Re: Raw water cooled mercruiser moored in salt water

I've never had an engine with closed cooling or installed a system on an engine already run for some time so it's hard to say, but I might pull off the thermo housing and the water pump on the front of the engine and take a look inside, if I saw a fair amount of rust then I would not put the closed cooling on, because the rust in the engine would clog the heat exchanger and then you'd overheat. But if there is no rust inside, it might be worth a try. These kits are not cheap though. At any rate, if you just run it and keep in mind you might get 10 more years out of it, you may not have major issues. With raw water cooling in salt the main problems people have is exhaust system related, the risers and manifolds will rust sooner than the block and cause water to get into the engine which will ruin it. So after about 5 seasons in salt (sooner if your exhaust system starts overheating, which is a sign the riser is getting clogged with rust) take them off and check them, they may need to be replaced that often. If you keep the boat long enough to have to repower it with a new engine, then put closed cooling on it. As others said above plenty of people do it, it's not the optimal set up but it can give long service anyway. The only other issue I have had related to salt is the thermostats get sticky and stick open a bit then the engine runs too cool. I usually put on a new one each season, they are cheap, its and easy job....

 

[Aloysius]

Re: Raw water cooled mercruiser moored in salt water

I'm in the salt water at my dock 12 months a year.

 

[JoLin]

Re: Raw water cooled mercruiser moored in salt water

I've seen Chevys rust through in 10 years, especially the new lightweight castings.

Sorry to disagree, but the 'friends' I referred to in my previous post (all with 20-year old original blocks) are all running GM (in one case, Chrysler). No Fords.

I can't imagine why anyone would want to buy a boat with a Ford or Chrysler engine it. Thay've been out of the marine market for way too long.

My .02

 

[sasto]

Re: Raw water cooled mercruiser moored in salt water

I can't imagine why anyone would want to buy a boat with a Ford or Chrysler engine it. Thay've been out of the marine market for way too long.

My .02

Why not? We have a 1974 Chrysler Marine engine, a '68 Harley Davidson golf cart, an '80 Cadillac Eldorado, and me. Out of the market for years.

 

[Aloysius]

Re: Raw water cooled mercruiser moored in salt water

We're in the water longer, and maybe water temp has some affect, but see many 10-15 year old engines with block rust through. Oxidation does increase with temperature.