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Fresh Water Cooled vs Raw Water Cooled Mercruiser Engines

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Fresh Water Cooled vs Raw Water Cooled Mercruiser Engines

Old 01-04-2009, 10:00 AM
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Default Fresh Water Cooled vs Raw Water Cooled Mercruiser Engines

I am in the process of buying a 2006 Sea Ray Sundancer 260. There are two 2006 boats similar equipped except one has FWC no warranty "as is" and the other is RWC with a warranty until 2012. The issue is if both are of similar money which one would you recommend and why. The warranty was sold by Sea Ray at the point of purchase and it is their extended warranty. Thanks for your insight as I am perplexed.
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Old 01-04-2009, 10:05 AM
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Default Re: Fresh Water Cooled vs Raw Water Cooled Mercruiser Engines

I can't believe they still make raw water cooled inboards in 2006???? Read the details of the warranty closely..........Salt water rots thing pretty quickly.....that is not to say that your fresh water cooled motor doesn't have salt water in it...(It does)...I would be skeptical of a 2006 boat being sold "as is" unless it is like 50% under book value.............
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Old 01-04-2009, 10:34 AM
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Default Re: Fresh Water Cooled vs Raw Water Cooled Mercruiser Engines

I should qualify as is after I have the opportunity to have the boat surveyed. The as is part is I guess take it or leave it. The issue is the engines ....is the recommendation to just but the fwc or is rwc ok as well?
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Old 01-04-2009, 04:37 PM
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Default Re: Fresh Water Cooled vs Raw Water Cooled Mercruiser Engines

Are you in salt water?
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Old 01-04-2009, 05:26 PM
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Default Re: Fresh Water Cooled vs Raw Water Cooled Mercruiser Engines

One has a closed loop cooling system - like a car
The other uses the water you are floating in to cool the motor - in salt water applications this forces replacement of some components every 4 to 6 years.
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Old 01-04-2009, 06:40 PM
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Default Re: Fresh Water Cooled vs Raw Water Cooled Mercruiser Engines

If I remember correctly back to my Mercruiser days, the raw water still cools the manifolds/risers and the heat exchanger. Because of this, these parts are still susceptible to corrosion from the salt.

There are freshwater flushing kits available for Mercruiser engines that may help you if you go that route.

I would go with the warrantied motors, as long as the warranty covers the parts failure from being exposed to saltwater.
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Old 01-04-2009, 09:12 PM
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Default Re: Fresh Water Cooled vs Raw Water Cooled Mercruiser Engines

signmansez - 1/4/2009 6:40 PM

If I remember correctly back to my Mercruiser days, the raw water still cools the manifolds/risers and the heat exchanger. Because of this, these parts are still susceptible to corrosion from the salt.

There are freshwater flushing kits available for Mercruiser engines that may help you if you go that route.

I would go with the warrantied motors, as long as the warranty covers the parts failure from being exposed to saltwater.
WRONG! Mercruisers manifolds are not cooled by raw water.They are part of the ccw loop.There is a block plate inbetween the risers and manifolds.The heatexchangers are half & half,but are made out of copper,no problems there.


Now,if one reads the warranty on these engines,the normal wear is NOT covered.So,if for some reason saltwater eats thru a cyl or any other part,warranty will not cover it.Raw water cooled engines can last as long as a CCW engine,even in saltwater.One big factor is how hot one runs the engines or how cold.Salt will start to plate out into the metals at around 175 drg.Also,it will plate out below 125 drgs,but will blow out once the engine gets to true operating temp of 145F- 155F.

"As is" sale of boats are the same "as is" in cars.It is up to the buyer to find out if there are any problems.Of course a full survey is a must.If the boat with the CCW system checks out and hours on the engines are ok,that is something you could use to help drop the price due to no warranty.Now an aftermarket add on ccw system would cost you around $750 plus labor per engine to install.Do the math.One thing for sure is,if you go to sell the boat any time soon,a buyer would look at a boat with CCW system before a raw water system.
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Old 01-04-2009, 09:36 PM
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Default Re: Fresh Water Cooled vs Raw Water Cooled Mercruiser Engines

There are plenty of kits to install a closed cooling system on any raw water cooled mercruiser. If you got room in the engine compartment it can even be an easy conversion. Not familiar with the 260 Sundancer but I can't imagine it being too expensive to do and its worth it. Especially it being a newer boat if your going to run it in salt water.

Go with the warrantied boat and spend the couple grand to convert it to closed cooling. Plus you can negotiate a good price since it is raw cooled and all. In any case if this boat is going to spend time sitting in saltwater I wouldn't go with an I/O. If you got it on a dry lift then I would consider it. Just my opinion.
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Old 01-05-2009, 06:22 AM
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Default Re: Fresh Water Cooled vs Raw Water Cooled Mercruiser Engines

I was thinking the same, buy the warrantied engine then add a fully closed FWC system. Make sure this addition would not void the warranty though!

I don't have personal experience installing FWC systems, but it was my understanding even on a full FWC system there are still components cooled by salt water. I found the following description helpful:

>>Q: Are there different types of fresh water cooling?
A: There are two basic systems.
Block and manifold, full system.

In these systems not only the engine block, but the exhaust manifolds as well, are included in the antifreeze system. The exhaust elbows, where the raw water enters the exhaust system, always remain on the raw water side. Full systems may not be possible on all engines due to lack of proper water connections on the exhaust manifolds and a lack of raw water pump capacity. This is often a problem with sterndrive engines. These problems can sometimes be solved but will get expensive. Typically, full systems are more expensive in terms of hardware and, especially, installation.

Block only, half system.

In "block only" systems, the most expensive part of the system, the engine block itself is on the antifreeze system. Exhaust manifolds remain on the raw water side. Half systems are less expensive to buy and much easier to install. When replacement exhaust manifolds are available at a reasonable cost, this half system is often the most cost effective. Carefully make an overall cost comparison between full and half systems before making a decision. <<
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Old 09-13-2016, 01:24 PM
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Regarding your options its a very simple matter, RWC engines are compromised by the salinity as salt is a corrosive. FWC engines never are compromised with the acidic action of salt water. As your cooling system, as far as the engine is concerned, the heat exchange is the reservoir for pure coolant, therefore salinity and silt do not pass through the engine block and cooling jackets. The best advice I can give you, as a marine technician for almost 40 years, hands down, is the FWC engine. Run a compression test, make sure you have at least 40 psi oil pressure after warming to normal operating temp which should not exceed 180 degrees. Additionally, I would suggest that you employ a marine engine surveyor prior to your purchase. In the end, you cannot loose.
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Old 09-13-2016, 01:47 PM
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Half cooled is a waste . The manifold failure is what kills engines . Full closed with a stainless riser is the best method to date , except for keel cooling . Just look at diesel systems to get the picture .
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Old 09-13-2016, 01:49 PM
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http://www.monitorpro.com/
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Old 09-13-2016, 01:52 PM
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6 plus year old thread, I am sure OP has already made his decision.
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Old 09-13-2016, 02:00 PM
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Originally Posted by AllisonMarine View Post
Regarding your options its a very simple matter, RWC engines are compromised by the salinity as salt is a corrosive. FWC engines never are compromised with the acidic action of salt water. As your cooling system, as far as the engine is concerned, the heat exchange is the reservoir for pure coolant, therefore salinity and silt do not pass through the engine block and cooling jackets. The best advice I can give you, as a marine technician for almost 40 years, hands down, is the FWC engine. Run a compression test, make sure you have at least 40 psi oil pressure after warming to normal operating temp which should not exceed 180 degrees. Additionally, I would suggest that you employ a marine engine surveyor prior to your purchase. In the end, you cannot loose.
You see the date of this thread
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Old 09-13-2016, 02:30 PM
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Originally Posted by highflier1 View Post
6 plus year old thread.
Newbieitis.....digging up threads that are years old to comment on.
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Old 09-23-2016, 03:30 PM
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Still has some value. I am considering a 340 DB with fresh water cooling but want closed cooling so response was very helpful.
thanks
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Old 03-10-2017, 12:47 PM
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Originally Posted by prockvoan View Post
WRONG! Mercruisers manifolds are not cooled by raw water.They are part of the ccw loop.There is a block plate inbetween the risers and manifolds.
That is correct for some Mercruiser engines, but the 454 Magnum Horizon engines on my 2000 380DA were designed and built w/ raw water cooled manifolds, risers and elbows.

After several years these expensive parts suffer from severe corrosion and must be discarded / replaced.

There was no provision for flushing or draining. I got tired of changing these parts so I redesigned the exhaust system from sitting 24/7/365 full of salt water, to permitting a manual flush after operation.

When I'm putting the boat away, I drain the salt water from the exhaust and from the raw water strainer, then use my custom-designed adapter to flush with fresh water, soapy water then salt away. When I'm all done I drain the parts bone dry.

My hope is this will all greatly extend the service life of my exhaust parts.

One big plus is the side exhausts would always be rust-stained gel coat after operation, now they are always shiny w/o ever having rust stains.
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Old 03-10-2017, 12:49 PM
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Thread from the dead!
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