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Questions & Answers about Fresh Water Cooling

1. What is fresh water cooling?
2. What benefits will I get from fresh water cooling?
3. Are there different types of fresh water cooling?
4. Should I have FWC if I keep my boat in fresh water?
5. How long will my raw water cooled engine last?
6. How long will my engine last with FWC?
7. My engine is several years old. Does it make sense to convert to FWC?
8. I thought that FWC was primarily for larger boats?
9. Some boat dealers tell me that FWC is not necessary.
10. If fresh water cooling is any good, why isnít it standard from the engine manufacturer?
11. I will probably sell or trade my boat before I have any problems due to lack of FWC, why should I convert?
12. How can I get galley water heat and/or cabin heat through FWC?
13. Will FWC affect my basic engine warranty?



Q: What is fresh water cooling?

A: It is the marine version of the cooling system that you have in your car.

Most marine engines start out as a non-marine engine and were designed to have a clean non-corrosive antifreeze coolant circulating between the engine and a "radiator". In the marine version of this cooling system (fresh water cooling), the radiator is replaced with a "liquid to liquid" heat exchanger. Sea water, instead of air, passes through the heat exchanger and absorbs the heat from the engine coolant and is then discharged overboard.

Many marine engines, for cost reasons, utilize the initially less expensive, but in the long run much more expensive, raw water cooling system. In this case polluted corrosive sea water, pumped directly into the engine, eats at the very base of a marine engine causing irreparable damage.

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Q: What benefits will I get from fresh water cooling?

A: The important advantages: Longer engine life; Simplified winterizing; Easy galley water & cabin heat.

Longer engine life due to:

No Corrosion - Most marine engines "rust out" rather than "wear out". By replacing corrosive raw water with antifreeze solution, you will prevent corrosion damage.

No Scale - Complete elimination of scale build up inside the water passages of the engine. The salts that exist in sea water, as well as "hard" fresh water, create scale that will restrict proper coolant flow and heat transfer.

Proper engine temperature - For best engine life and performance your car operates at a temperature much higher than a raw water cooled marine engine. By converting to FWC you can bring the engine temperature up to proper level using a higher temperature thermostat. This, is turn, will give you improved fuel economy, less engine wear, no crankcase condensation, no oil dilution, and no sludge.

Simplified winterizing - By keeping an antifreeze solution all year round, winterizing is simplified.

Easy galley water & cabin heat - Galley water heaters and cabin heaters utilizing excess engine heat are easily added to the system.

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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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Q: Should I have FWC if I keep my boat in fresh water?

A: Yes, to simplify winterizing, eliminate all corrosion and debris damage.

Although lake and river water is not as harmful as sea water, it often contains scale forming salts, pollutants, mud, sand and other marine organisms which often can be quite damaging.

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Q: How long will my raw water cooled engine last?

A: Impossible to say.

Water conditions and, therefore, corrosion rates vary from one location to the next. The main problem id that since the damage is internal and completely hidden, there is no accurate way to measure the damage and predict when the engine is going to fail.

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Q: How long will my engine last with FWC?

A: It will wear out in a normal fashion.

Most marine engines "rust out" rather than "wear out". With an average of no more than 50 hours annually on pleasure boats the wearing out for an engine that is FWC and well maintained should be measured in decades rather than years.

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Q: My engine is several years old. Does it make sense to convert to FWC?

A: Definitely.

Ideally a conversion to FWC should be made when the engine is new. That way you can prevent any damage to your engine. But by installing FWC on an older engine, you will prevent further damage and you will enjoy all the other benefits from FWC.

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Q: I thought that FWC was primarily for larger boats?

A: It may have been, but should not be.

Factory fresh water cooled engines are usually installed in larger, more expensive boats. The additional cost is fairly low in proportion to the total cost of a larger boat. However, in smaller boats the engine represents a far larger proportion of the boats total value. The owner should, therefore, be more concerned with the condition and value of his engine, or he will pay for it in the long run in the form of premature re-powering or lack of resale value.

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Q: Some boat dealers tell me that FWC is not necessary.

A: It depends on what you mean by necessary.

FWC is not necessary in the sense that your engine will stop functioning tomorrow if you donít have it. Nor is changing your oil and filter and many of the other things that you do in order that your engine will give you maximum life and performance. The benefits of fresh water cooling are more of the long term type. In order to keep the cost of a new boat to an acceptable level, some dealers hesitate to recommend options that are not absolutely necessary when the boat is purchased.

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Q: If fresh water cooling is any good, why isnít it standard from the engine manufacturer?

A: It is simply a matter of cost.

The boat building business is very cost competitive. Most boat builders do not want to spend any more money than is absolutely necessary on the power package and, therefore, specify the less expensive raw water cooled engine. Improvements such as FWC are usually left to the ownerís option.

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Q: I will probably sell or trade my boat before I have any problems due to lack of FWC, why should I convert?

A: The trade-in value of a boat with FWC is much higher.

A FWC system on your marine engine is the best way to defuse the time-bomb that a raw water cooled engine represents to a potential buyer. A marine engine is not like the tires on a car, where it is possible to judge how much life is left. Corrosion damage is completely hidden and impossible to measure. A FWC system shows that there are no unpleasant surprises waiting. It also shows that the previous owner was knowledgeable and probably in every other respect took good care of the engine.

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Q: How can I get galley water heat and/or cabin heat through FWC?

A: It is a simple addition.

Your marine engine can provide this heat in the same way as your car engine provides car heat. A full range of galley water heaters and cabin air heaters are available. Installation is an easy do it yourself plumbing job.

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Q: Will FWC affect my basic engine warranty?

A: There is no reason why it should.

There is nothing in a Monitor, San Juan, or Sea Kamp Fresh Water Cooling system that can do harm to the engine as long as the system is functioning normally. Because of their high performance design their systems have a very high safety margin due to normal cooling performance.

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Last modified: October 27, 2007