Raw-water to fresh-water cooling conversion

[Catamount]

The Yanmar 2QM15 engine in my 25-year-old boat apparently never came with a fresh-water cooling option, thus there are no aftermarket heat exchangers specifically designed as replacements. At one time, Sen-Dure offered a conversion kit, but not anymore.

So I'm looking for advice on how to determine what would be an appropriately sized heat exchanger. For the tubes-in-shell types, they're spec'd by shell diameter and tube-bundle length; for other types (spiral plates, etc...), they're generally spec'd by effective surface area. How can I determine the effective surface area of the tube-in-shell types? (I would need to know the number of tubes in the bundle, as well as their diameter, in addition to their length -- is that information ever available?).

Then, how do I decide how much surface area I need to cool my little diesel? I guess I would need to know the operating temperature of the engine, the temperature of the raw water, and the flow rates of the two pumps (circulating and raw water).

Any suggestions on how to proceed? And any thoughts about where to purchase an appropriate heat exchanger?

Thanks,

Tim

[Rick]

Having done that before (using the Sendure heat exchanger) I can mention some of the problems. What is most important is the salt water flow rate dictated by the belt ratio driving the added salt water pump and the pump size.

Strive to install the largest volume pump (within reason) that you can so that you can drive it as slow as possible in order to get the best pump life. You are on the right track if the pulley size on the pump is equal to or larger than the crank driving pulley diameter.

Try to get a heat exchanger with not too small tubes that will not clog. Try to get an exchanger made with a passive alloy like that used by Yanmar in their stock freshwater engines. They are more expensive.

Expect any anodes installed to protect non-passive alloy heat exchangers to disappear rapidly if you do not bond the engine, raw water intake, strainer, heat exchanger, pump, prop shaft, etc. Even then you must check them often because the volume and speed of the raw water passing protection anodes wears them away and you don't want the remainging "stub" of zinc to tear away and lodge in your exchanger tubes.

Change the thermostat in the engine to a higher temperature one. Yanmar uses colder thermostats in the raw water cooled engines and if you keep the original one you will not gain an improved efficiency that any engine gets by operating at a higher temperature (without causing problems). If you have to convert back don't forget to return to a colder thermostat else the salt water will make terrible deposits in your engine water jackets.

[Alan Wheeler]

Excellent Reply Rick.
Tim, Just to add. Although there is no 2QM heat exchanger avaliable, you can use the first one avalailable for the next size up Yanmar. It's not important how big an exchanger is, Just as long as it's not too small, it's just praticality and price. You can use as big as you like, it's the thermostate that controlls the heat of the engine it'self, not the exchanger.

[geohan]

Tim

We fabricated a heat exchanger for a 12- HP Universal Yacht Twin with two 16-foot lengths of 3/8" copper tubing which required the installation of a thermostat to get the temperature up to 180 deg f. and which performed flawlessly for the 15 -years before we sold the boat.

Details upon request.

George

[BC Mike]

There is always the Yanmar help site.
This motor is a real diesel not a downstream unit. If the zincs are in good condition it will run for a long time digesting salt water. So says my Yanmar dealer. The engine does not run hot enough for the salt to remove itself from the water. The after market heat exchangers are not the best for this motor. Again quoting my dealer. You could flush it with fresh water once in a while and try not to be too concerned. Probably a good idea to remove the cylinder liners once every twenty years and clean inside the block.
Michael

[Catamount]

Mike, I have been reading up on the issue at the Torresen's Marine Diesel Direct forums.

From what I can tell, the main issue with continuing to run the 2QM15 with salt water is corrosion of the exhaust manifold, which part is no longer manufactured by Yanmar -- so if it goes, there goes your whole engine. Perhaps one could have a replacment custom machined if necessary, but why not try to prolong the life of this manifold for as long as possible?

That's perhaps the main impetus for converting to FWC.

FWIW, Sen-Dure apparently still offers the 2827-1-5 heat exchanger that was part of their kit, but so far they haven't been able to tell me any of its specifications. They also offer an 10446-1-5 heat exchanger that is described as being a 2827 with 6" added. I sure would like to know more about these units, in terms of the technical details.

Rick, can you tell me the basic dimensions of your SenDure heat exchanger? (or anything else about it, for that matter)

George, indeed I have contemplated building my own heat exchanger. They're really not that complicated a device, after all. I would be interested in the details of yours (you can e-mail: catamount@nh.acadia.net).

Alan, yes I could use a heat exchanger intended for another engine -- I guess my main concern is making sure that I get one that will be sufficiently large to do the job, but no so big that I start dragging my transom around! Thus my interest in figuring out how to size the thing.

Rick again, your information about the pitfalls of the conversion is very helpful. A fellow who goes by "capnjim" has posted complementary information over on the Torresen's Marine Diesel Direct forum, so between the two of you guys, you've covered the issues pretty well.

Take a look at: http://www.spirec.com/index.htm -- what do you guys think of these spiral cylindrical plate heat exchangers? Might be hard to clean out salt deposits, but being constructed of 316 stainless they should stand up to a mild acid soak every now and then. Here's a cross section from their site:


And here's another option: http://www.kineticengineering.com/encoil.html I gather these are made of 304 stainless. Here's a cross section:


Do these spiral plate types have any disadvantages over the tube-in-shell types? I hear that the tube types could be cleaned out by pushing the built-up gunk through the tubes with brass rods or blunt dowells, but a lot of folks advise against this because of the potential for doing serious damage to the tubes.

Thanks for all your input. Keep it coming!

Regards,

Tim

[BC Mike]

I can agree with your logic about the exhaust mainfold, but I would like to study the fresh water unit to determine where the salt water goes, after it goes through the heat exchanger. If it exits through the exhaust manifold the same problem exists, but we have protected the engine. If the manifold runs dry it will run hot and I do not know if it can take the heat.
One way of cooling the engine is to run cooling tubes down in to the skeg, or along the hull. This cools the engine with an anti freeze mix and the exhaust runs hot like your car.
Nigel Warren wrote a book about cooling motors in boats. I do not have it but would like to. Could you get it and read it and then sell it to me cheap?
I have a 2.5 litre Nissan diesel that I was going to put in my aluminium fishing boat using cooling tubes and a dry exhaust. It is on my to do list, which is a bit on hold as I wait for the farm to sell. We could always just run the 2QM15s the way they are and spend the $$ when they finally quit. But that does seem a bit silly as they are built to last forever, and are rebuildable.
My experience with heat exchangers is that they need service on a regular basis, and the folks that use them on boats in fresh water, manage to freeze them.
Michael

[Catamount]

Mike,

I would dump the sea water from the heat exchanger into the exhaust at the mixing elbow which follows the exhaust manifold. The manifold itself would be cooled by the freshwater circuit.

Regards,

Tim

[BC Mike]

Yes , that makes sense. I would still like to study the system, but the designers must have figured it out. Please keep me posted.
I have a 1979 2QM15 that runs great and has never seen salt water, but all that could change when I take it to the ocean next year.
Michael

[Rick]

Tim,
I no longer have that boat (loved it and the engine). Best that I can recall is that the exchanger was only about 18 inches long and less than 2 inches in diameter. Like Wheels said, it doesn't take much of one to do the job. In addition, I was surprised to note that, although I had installed a conversion "kit" that the water pump quickly wore out. I slowed it down by a factor of THREE and there was never any indication of running too hot at any rpm and the pump didn't give any problem after that. It seems that at idle as long as there is sufficient water mixing with the exhaust elbow to keep the hose cool and the water life working well that there always will be sufficient water at all higher rpms to cool the engine under load (assuming that you are not over propped).

My experience with stainless, and 316 is not the best in this application, is that other than a prop shaft that can be repeatedly imspected I don't like using it below the water line or in constant immersion with salt water, especially warm engine water. Note that Yanmar uses a copper nickle alloy, expensive yet very passive and known to be good in this application. At one time I noticed that there was a manufacturer producing such a product yet don't recall the name. One big problem with 316 is passivating the welds properly and, from the looks of the photo, I doubt that they did that. Others may have good comments in this regard.

[windthief]

Here is some food for thought, and what i usually tell my customers who want to put on a fresh water cooling system after long time salt water use, the salt has impregnated itself in the casting of your engine and will never be completely removed. so you will be enclosing this salt in your block and manifold.

If your really determined to do this conversion you will want to call some one like San Juan engineering 360-734-2788 or Sea Kamp 360-734-2788. Be sure to get the cupro-nickel blended heat exchanger.

best of luck.

[Alan Wheeler]

Wow? isn't there some opinions to this topic. Don't get me wrong, I am not saying anyone is wrong, just a lot of approaches.
Windtheif, a good fresh water flush and then chemical flush will remove any worry of Salt.
Rick is right about SST heatexchangers. Although they are used, there are also inherent design problems with them. The best material is copper and it isn't hard to build an exchanger, just fiddly. The hard part is a cooled exhaust manifold. But you can use the regular manifold and just lagg it. The riser will need to be lagged anyway. Oh and Riser....
Important point if dumping cooling to exhaust, ensure you have a Riser directly after the manifold. On the downside of the riser, fit the water injector. This is so no water can come back up the riser and down into the exhaust and thus engine.
There is NO ONE perfect way of cooling an engine. Every design has advantages and disadvantages.

[Jentine]

Why do you want to change the cooling system after 25 years. If the system has functioned all this time without blowing the engine, what is the point? Do you have too much time on your hands or too much money that you need a hole to throw it into? If the reason is that you are having trouble with the raw water cooled and manifold and riser and they need to be replaced, there are easier solutions to your problem.
I would investigate ceramic lined manifold and riser as an alternative. I have owned power boats with raw water cooled engines and aside from the manifold rusting to the point of being useless or corroding through the internal jacket, the system is bulletproof. A ceramic lined manifold makes it more so. The cost of the ceramic manifold is only slightly more than the standard cast iron manifold.

[Catamount]

Jim,

Thanks for asking the question. The boat (and engine) is new to me -- so it's not like I'm deciding to do this all of a sudden after 25 years of experience with the raw water cooling.

Although it is not much to look at, as far as I can tell so far, the engine is still running fine. But there is significant corrosion on the exterior of the exhaust manifold, and my surveyor recommended that I "arrest the rust and monitor the conditon of the exhaust manifold and replace as necessary."

So at the least, it seems that I need to pull the manifold and clean out the cooling conduits of any and all accumulated crud, corrosion, and scale (boiling it in radiator cleaning fluid, poking and prodding with stiff wires, and maybe flushing with acidic and alkali washes).

Once I get that done, I suppose my options are to: (1) keep going with the raw-water cooling and just hope for the best, or (2) convert to FWC in hopes of extending the life of exhaust manifold (and the engine). Whether I convert to FWC or not, when (if?) the exhaust manifold finally fails, I could (A) re-power with another engine, or (B) have a new exhaust manifold custom made (the orginal replacement part is no longer available).

I assume that having a new manifold made would be a less expensive than re-powering with a new engine, but I suspect that converting to FWC now will be less expensive (probably less than $500 in parts) than having a new manifold made, and maybe has the potential to extend the life of the engine for a long time to come.

The ceramic-lined manifold and riser sounds like a great idea, if (when?) it comes time to replace the existing part. Do you have any suggestions as to where I could get one of these made, in the event it became necessary?

Wheels, what does it mean to "lagg" the manifold or riser?

Windthief, I'm not sure I understand how the engine could be permanently "contaminated" with salts. Are you suggesting that the salts have diffused into the solid cast iron, and will be diffusing back out of the iron indefinitely after the conversion? Or do you mean that cooling conduits throughout the engine will always have some degree of corrosion or accumulation of crud and scale left over from the raw water cooling that we'll never be able to get all out?

Again, thank you all for your continued input.

Regards,

Tim

[Alan Wheeler]

There is one hot area with the a manifold. It is directly after the cooled exhaust maifold, up the riser to the point of where the cold water is introduced intot he exhuast stream. Lagging, (maybe a different term to you, or maybe I have spelt it incorrectly) is where you wrap a heat resistant fabric around the exhaust to stop heat radiating out inot the engine room. Years ago, Asbestos was used for this, but no longer of course. I have used a High temp rated fibreglass rope. Then covered it in a special aluminium foil to protect the rope and increase the heat retention. It is cold to the touch.