New to Salt Water - cooling systems

[tuffr2]

I am looking at a lot of boats with an open cooling system. My 1st thought is these are bad...but I see alot of them on the ICW and a lot around inlets.

Do closed cooling systems just add complexities without huge benefit?

I see lots of outboard powered boats. That is an open cooling system...correct?

So, should I even look at open cooling systems or not? What is the big plus of a closed system?

[Kristoff21]

IMO, and as a sailor and powerboat owner of many years, my experience has been that any benefits of closed cooling are negated by the added complexity of the additional closed loop hardware to such an extent that there is little to chose between them. I've had all types, and the maintenance bills haven't varied due to the type of cooling system over the mid to long term.

What really does damage, is boats with open cooling that are used in salt water and then left sitting idle for a long time in between uses, say on a mooring. Most people who have smaller powerboats and who use them infrequently lift them out regularly to flush with freshwater, so that's no problem, and those that are used as liveaboards are in constant use so that's fine too.

Even if you have closed loop cooling you have a drive leg that is raw water cooled anyway.

The one design that is probably worth having in terms of anti-corrosion is closed loop with shaft drive. But if you don't want a shaft drive boat (their are drawbacks) I wouldn't worry too much about the type of cooling as long as you are either a) using the boat regulary, or b) flushing regularly.

And yes, outboards are open cooled, but most can now be flushed with the engine off and in the tilted position making it a doddle to flush after use if you have freshwater on hand. It's hard to flush a sterndrive (I/O for you Americans ) boat when in the water. Hard, but not impossible.

[Pizzazz]

Fresh water cooled engines are better and more efficient mostly because they get warm faster and run hotter than single loop cooled engines. The corrosion resistance is a secondary benefit.

On a sailboat, the engine typically gets used for 5-15 minutes at a time (get out, raise sail and the reverse when coming in). It takes 1-2 min for a fresh water cooled engine to get to operating temp vs. 15-20 min for salt water cooled. Now calculate the impact on efficiency, carbon deposits and engine rebuild frequency.

[Kristoff21]

I've heard that theory often quoted, but don't most yachts have a thermostat that restricts flow during warm up?

So the sea is just acting like a big (saltwater) radiator?

That's a genuine question, I don't know if they have or not, but I've always assumed they must have as it seems so logical.

[Cadence]

My humble opinion is don't have anything in salt water without a heat exchanger unless you can haul it out and flush it after every use.

[carlheintz]

Cadence is absolutely, 100% correct. Warm salt water is as corrosive as acid. Salt water is our enemy. You must have a heat exchanger.... you don't want acid surging through your engine. Yes, closed systems are a hassle. More hoses, more stuff to break, etc. etc. But they save your engine.

[Lancerbye]

There are probably thousands of raw water cooled Yanmar 3HMs out there. They have thermostats and zincs that are in the blocks to prevent corrosion.

[ranger58sb]

Originally Posted by Lancerbye

There are probably thousands of raw water cooled Yanmar 3HMs out there. They have thermostats and zincs that are in the blocks to prevent corrosion.

How do thermostats or zinc anodes prevent saltwater corrosion?

-Chris

[Shrew]

Are you sure you're seeing as many 'open cooling systems'? Even if an engine is rigged with a closed system (e.g. engine coolant being circulated through block) the heat exchanger, and in many cases the exhaust manifolds & risers are running an open cooling system. The water being discharge with the exhaust is not being run through the block.

[rwidman]

If you are boating in salt or brackish water, a closed cooling system (coolant in the engine and a heat exchanger to cool the coolant with sea water) will prolong the life of the engine. The engine will be designed to run at a higher temperature and will be more efficient.

Higher quality (and higher priced) boats will have closed cooling systems. If you want a serious boat, you will want a closed cooling system.

[patprice]

Originally Posted by rwidman

If you are boating in salt or brackish water, a closed cooling system (coolant in the engine and a heat exchanger to cool the coolant with sea water) will prolong the life of the engine. The engine will be designed to run at a higher temperature and will be more efficient.

Higher quality (and higher priced) boats will have closed cooling systems. If you want a serious boat, you will want a closed cooling system.

Hot water at the shower and kitchen sink from a closed system.

[Nicholson58]

Direct cooling is great for all engines run strictly in fresh water. Better reliability and better cooling. The only other consideration might be growth of Zebra muscles or other fresh water critters that can be isolated from the engine with a glycol loop and heat exchanger. Zincs last almost forever in fresh water.

If in sea water, you must have a glycol loop and heat exchanger. I replace the heat exchanger zinc every four weeks. I carry a spare exchanger and a spare sea water pump as well as a few impellers. My Westerbeke 115 HP six is 1984 and no issues.

Outboards are prone to corrosion of the lower housings and must have regular attention, rinsing and draining if possible. They won't last as long as a glycol cooled inboard.

[Cheechako]

Nothing about a seawater cooled engine should NECESSARILY make you run away. But age and use can be a problem. It could be full of corrosion and debris, or could be fine for your use.
I have not found freshwater cooled engines to be much trouble, but there is more "stuff" involved.

[rwidman]

Originally Posted by Nicholson58

Direct cooling is great for all engines run strictly in fresh water. Better reliability and better cooling. .........

Not really. The proper dilution of engine coolant and water is more efficient than water alone. It doesn't matter though as long as your cooling system keeps the engine within the proper temperature range. As long as it does that, there's no "better".

If in sea water, you must have a glycol loop and heat exchanger.

"Must" is a pretty strong word. Too strong in this context "Recommended" would be more appropriate.

Outboards are prone to corrosion of the lower housings and must have regular attention, rinsing and draining if possible. They won't last as long as a glycol cooled inboard.

Outboards are self draining in the vertical position but are ideally rinsed after being run in salt water. I agree an outboard is not likely to last as long as a diesel engine with a closed cooling system. Compared to a gasoline inboard, this may or may not be true.

[Sunsetrider]

My open system is a 40-year-old engine, run (at least currently) in fresh water. I plan on taking it "to sea", and it strikes me as somewhat foolish to worry at this point about "prolonging engine life" by retrofitting a heat exchanger etc. My sort-of plan would be to run it up into freshwater inlets from time to time, when possible.