Freshwater vs raw water cooling

"My previous problem with my 5

"My previous problem with my 5.0l Mercruiser was solved with help from this board. I really appreciated the advice that I received.

After getting more involved with the engine of this boat than I had expected to, I have become concerned about the cooling and the life of the engine. When I got the boat new I did not consider cooling options for saltwater. My boat has a 3 year old 5.0l mercruiser with the Alpha 1 with raw water cooling. I use it exclusively for saltwater, and had assumed that the cooling system was designed to be able to handle exposure to saltwater. Apparently not the case.

I am now considering other options:

1. How can I best flush the motor while it is in the water; or can I? I currenly leave it in for about 2 weeks, pull it and run it for about 1/2 an hour flushing it with freswater,
2. Should I install a freshwater cooling conversion kit?
3. What conversion kits would you recommend for dependability and for ease of installation?
4. Is there any way that I can remove any crystalized salt in the system that may have developed over the last two years?

I am starting to undertsand that preventative maintenance is essential with a boat engine.

Thanks for your help,
Paul"

"Paul,
You know that five hun

"Paul,
You know that five hundred you saved on the ignition parts,take it and buy the heat exchangers and parts to hook them up.
Then you can leave anti freeze in the system year round except the fresh water side of the exchangers.
Try amarket.com for the exchangers and parts.
If you call these folks they will walk you right through the whole job. Nice people good products at great prices. If they can't help they know who can. Good luck. A.S."

"Paul, It is a bit late to ins

"Paul, It is a bit late to install the freshwater cooling system, the salt has had it's way with the block, risers and manifolds (intake and exhaust). In addition, Mercruiser recommends a through-hull raw water intake to adequately cool the heat exchanger on all V6 and V-8 motors. Realistically, the money spent on new exhaust manifolds and risers in comparison to the FWC system and it's installation, over the course of the boat's life is comparable. You will need new manifolds in 3-5 years from now, risers 1 year or so sooner. Start imspecting the risers annually, by removing the rubber sleeves, in a year or two. A year after they get holes (or nearly get holes) through to the exhaust passage, it will be time for manifolds. Make sure your thermostat is the 140 degree version, as that keeps the corrosion down. I keep my 4.3LX in salt water 6+months a year and got 10 years out of the manifolds."

"Chris,
Sounds kind of hopele

"Chris,
Sounds kind of hopeless. Are you saying that there is really nothing I can do to significantly reduce deterioriation in the motor from salt? Is there no chemical flush that I could use to stop or slow corrosion? The fresh water cooling wouldn't help?
Paul"

"I've been using a product

"I've been using a product called saltaway from west marine. I've been told by numerous mechanics that when they tear down an engine that's been maintained using this product, the damage from saltwater is greatly reduced. I operate my boat soley in saltwater also. At the end of the day, I put the boat on the lift and flush it. Takes about 5 minutes. The other reccomendation I would tell you is look at stainless steel manifolds and risers. The ones from Stainless Marine use a hose between the manifold and riser. This eliminates the possibility of water entering the engine through the gasket. They're not cheap, but they carry a 6 year warrenty."

"Thanks for the information. I

"Thanks for the information. I spoke to a mechanic up here about this and he indicated that adding a conversion kit now, after having been in salt for over two years, could actually cause problems. He said that it could cause hot spots in the engine and manifolds, causing them to fail earlier.
Sounds like I should set aside some money and just plan on replacing parts over the next few years?
Paul"

"There's alot of different

"There's alot of different theories flying around, but the bottom line is if you stop exposing the iron to seawater and put it in a corrosion resistant environment, you will significantly slow the corrision process. There are a few things to keep in mind:
- the type of corrision you're dealing with in salt water is Chloride Pitting. This tends to cause the metal to flake away in chunks. If the chunks are big enough to get stuck somewhere, they will lead to more problems. (ie hot spots, and more rapid corrosion. Corrsion is temperature dependant!)
- even with fresh water cooling, the risers/elbows are still cooled by raw water... therfore will need to be replaced routinely (3-5 years depending on the amount of use.)
So really, you need to consider the current condition of the engine block and manifolds and decide if there is enough there to salvage for long term use. The engine block, even though exposed to seawater for an extended period, is probably not your weakest link.
I would say it's feasable to replace the manifolds and risers, they're due anyway, take a good look inside the accessible water passages, and make an decision on whether the block is worth doing the fresh water conversion.
I installed a fresh water cooling kit (San Juan Engineering, bought through www.i-netmarine.com) on my 5.7L merc, which had roughly two seasons worth of exposure to salt water before hand.
There were some chunks in there, that flushed out pretty easily and it's been running great since.
After the first couple of months I flushed the cooling system again, and there was a good bit of fine particulates in the coolant. Two years later, it's still very clear.
Hope this helps."

"Paul, All is not lost. My &#

"Paul, All is not lost. My '88 4.3L Mercruiser motor is kept is saltwater. With the right (140 degree)thermostat, the block lasts long enough(20 years). The manifolds and risers are a bit pricy ($500/set) and last 6-8 years. Watch the rust on stuff like the timing cover and oil pan. Actually all the light steel parts are rust bait."