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Date: 15 May 2015. Marinizing the Cooling System of a Tractor.


Update. 21 May 2015. After speaking at length with the mechanic this morning, I went back and corrected (below) the drawings. I had the flow of water the opposite. Basically, water is pumped into the bottom of the box and exits to the heat exchanger out the diagonal. Also, the place where the raw water is injected in my drawing was too high. It is much lower. Pictures a-okay as of today.

Further on this will be upcoming. I am relieved. Still, I wanted to correct this article ASAP. J.

Transforming a tractor engine into a marine motor is not for sissies. Fortunately, I have back-up and progress is being made. My Kubota 18hp [from Yanmar Tractor Parts] is a gem. And it is many thousands of dollars less than the marine Yanmar motors so prevalent in boats today. For the budget minded, that has a great deal of appeal.

Specifically, you can buy an 18 hp Yanmar marine engine with transmission for in the neighborhood of $14,000. Plus installation of course.

Or, contact a place like Yanmar Tractor Parts for a different option.

A tractor motor adapted properly is a viable choice for those of us without deep pockets. And yes, Kubota motors are comparable with Yanmar.

Kubota isn't labeled marine therefore the price is far more to my liking. Their factory marinized line includes Beta and Universal.

Still, utilizing a tractor motor does add a level of complication. Cooling is an issue. In that regard, the men at Just Right Marine in Carrabelle along with a welding shop in Tallahassee created for me a wonderful manifold. Mine is 100% stainless (be still my heart!) and beautiful. It should outlast the boat.

The welding that is magnificent. And no, I do not use that word inappropriately. Check out the amazing work done by a Professional (capital "P") at Tallahassee Welding and Machine Shop [http://tallawelding.com/]

Any welder who can produce seams like this does not need a business card.
Simply a picture of work well done is more than sufficient.

(That's a temporary wrap of silver tape on the coolant pipe.)

Each person who has seen this manifold has commented on the welding. Around the Just Right Marine store, everyone has asked who did it, and how much. As for the who did it, contact Kenny Small at 850-576-9596. And the time? Eight hours. There was a CAD (computer drawing) involved too.

Daddy was a welder. Heck, he even built the steel 40'er I grew up aboard. Still, I will say without equivocation that the seams on this piece are as fine as I have seen. Impressive is not too strong a word.

If you need professional welding contact Kenny Small, the owner of
Tallahassee Welding and Machine Shop


Details on the design can be found in the Stainless Manifold Ordered (tractor motor adapted for boat) piece. That article goes into more detail. For your convenience, I have copied the following box from that article.

Manifold Design for Tractor Motor Used in a Boat



My sketch could be better, so let me clarify a bit. First of all, there's a heavy duty big stainless box that surrounds the pipes. Those pipes (RED ARROWS as seen above) carry the exhaust from the engine. Fluid, a combination of anti-freeze and fresh water, will fill said box. The solution will flow in from the bottom left corner and exit the top right. That water/anti-freeze concoction will go into (and come out of) a separate tank.

A sturdy stainless box encloses the Schedule 40 (heavy, thick walled stainless) 1.5" pipe. The STAINLESS PIPE carries hot exhaust air through the cooling manifold box. A NIPPLE at the top will deliver raw water into the pipe. That will further cool the exhaust.

The BLUE ARROWS AND STARS show water and antifreeze as they flow through the stainless box. There will be an external closed fresh water tank. That unit is a Heat Exchanger.


Addendum April 2015: My drawing is a bit off from the final result. The changes you will note are the box (aka manifold) is now U-shaped. That will allow better flow of the fluids through it.

Also, the coolant goes in at #1 and fills the box/manifold. That coolant, a combination of anti-freeze and water, exits at #2. There is an upward flow of cooling water being pumped through the unit. 

Photo updated 21 May 2015.



Photo updated 21 May 2015.



Here's how the Just Right designed manifold works: (the manifold is the U-shaped box)

As illustrated below, the red arrows shown are actually a schedule 40 pipe that the air flows through. I've tried in Paint to draw it and failed miserably.

Proof positive that Windows Paint and I do not always get along well:
Photo updated 21 May 2015.


Red hot air exits the engine. That flange at the far left bolts to the engine. There is a bracket under the middle of the unit to support the weight.

Photo updated 21 May 2015.

Air flows through the Schedule 40 (thick walled) stainless pipe. (red and white arrows, beginning on left) toward the exit of the manifold on the right.

Green coolant enters the manifold at the bottom right and exits through the diagonal on the left side. It's fed by a pump. This will be a mixture of antifreeze and fresh water. The coolant will fill the box. The red pipe (see above) will be surrounded by that mixture of anti-freeze and water.

Blue raw water* enters the red pipe to add cooling water to the hot air. The water and air will mix just prior to the exit of the manifold on the right via a hose. The raw water's sole job is to cool the pipe so the hose won't deform from the heat.


From there the Air and Water will flow through a water muffler (to quiet the sound) and then out the side of Seaweed. For those interested, it is a Vernier Lift Muffler. There will be no *raw water in my engine. That should keep the components in good shape for a long time.

*Raw water is the water found outside the boat (river water, ocean water, lake water, etc.)

This is my water muffler:

The water muffler (aka water-lift) is part of the cooling system. It helps quiet the sound too. Water and air will flow through the chambers in it, then exit out the starboard side of Seaweed.

Size is difficult to determine from this angle of the photo. The Vernier lift is a bit smaller than a five gallon bucket. Small engine equals small water muffler. The obverse is true as well, i.e. a larger engine requires a much larger water muffler.


According to Brian on LCV (Low Cost Voyaging on Yahoogroups), "As far as water-lift sizing, the larger engine does not always have the larger muffler. The inlet and outlet size is larger on the larger engine but the volume is determined by the hose run after the muffler and how much water will run back upon shutdown."

This is a nifty design. Just Right Marine figured it out. And Tallahassee Welding and Machine Shop created the magnificent manifold.

Being able to utilize a tractor motor in a boat means I'm saving money. The quirks to marinize her do add to the final tab. Of course, I'm still way ahead of the $14,000 price tag for a new Yanmar 18hp diesel marine engine even with the complications. That's $14,000 plus installation!

Photo updated 21 May 2015.

The coolant (green) side required a water tank. The water and antifreeze will circulate through a heat exchanger aka external water tank. It's a closed system* and will eliminate the difficulties that can occur when raw water runs through a motor.

*Closed system: The same fluid flows through and returns to the tank aka heat exchanger. There is no overboard discharge for this portion of the cooling system.

Here is a picture of my oversized black heat exchanger and the stainless manifold:

That heat exchanger is far larger than necessary for my little Kubota from Yanmar Tractor Parts. It was free and therefore is perfect. This coming week it will be bolted to the forward bulkhead in my engine room.

Hoses will be attached and soon, really soon, my Seaweed should be mobile. I am excited and look forward to swimming off the boat in green water again. I have missed that.

Life is good afloat. And progress is being made.

I am entirely grateful for the feedback regarding my cooling system. THANK YOU does not even begin to express my sincere appreciation for the education. J.

PLEASE NOTE: I posted links to this article on several sites and received feedback. Below are some pertinent points to consider should you opt to power your boat with a tractor motor. My responses are in italics.

Update 21 May 2015. Please bear in mind these comments were prior to the updated pictures. Originally I had the flow of water backwards. That is fixed now. Also the entrance of the raw water was just after to top elbow. The water enters exhaust pipe just prior to pipe extension on the far right. A hose attaches to that pipe, and from there the raw water and hot air flows to the water lift muffler and out.

With apologies. I am woman, and having been married can attest to making mistakes. For proof positive of that, contact my former husband.

Comment from DougR on CruisersForum: Your project looks like a lot of fun. As you mention, repowering a trawler with a tractor engine isn't for everyone, and there are lots of things which must be considered. Seeing as you threw the project out there, I thought I might make a few comments that might save some grief down the road.

The piece of stainless steel art that you refer to as an exhaust manifold might more properly be called an exhaust elbow or riser. From the photos, I see that it is probably designed to bolt onto the factory dry manifold at the two bolt flange. What I can't see are any other brackets to provide additional support. This is a rather long heavy part to support only with the two bolt flange, and when it gets full of water it will be even heavier. Without substantial additional support it will almost surely crack or cause the dry manifold to crack.

You're correct DougR, and yes a mounting system for the stainless manifold, or riser, is in the works. Even empty, it's a heavy piece.

As I understand your drawings, the freshwater coolant will enter close to the exhaust pipe entrance, and exit on the bottom on the other end of the unit. The problem I see here is that there will be a large amount of air trapped at the top of the rise, with no way to purge the air out. This air will cause expansion problems within the freshwater coolant system. I suggest you add a bleeder valve at the highest point of the water jacket to get rid of the air when the system is filled.

Interesting point. I'll take that up with the mechanic tomorrow. Thanks.

This system will probably last for many years, but welded stainless exhaust systems in contact with salt water have a history of pitting in and around the welds. When pitting occurs the engine coolant will disappear out the exhaust without a trace.

I think the heat exchanger you have chosen will have enough heat rejection capacity for the engine, as well as the heat that will come from the exhaust elbow, but just be sure the plumbing on the freshwater side of the system is as direct as can be, and has low pressure drop. You want to be sure the circulation pump has the ability to push an adequate volume of water.

Good luck with the project DougR.

And the following day Doug wrote: I did a bit more thinking about the bleeder valve, and while I think it is necessary to bleed air from this high spot, I think I would do it slightly differently.

As you might know, engines frequently manage to put "air" into their freshwater cooling systems. This can come from minute compression leaks, suction leaks at the circ pump seal, etc. and most engines have some sort of bleed system to get this air out of the engine and into the expansion tank. It is not unusual to see bleed hoses running from high spots on the engine, such as turbochargers, after coolers, etc. to the expansion tank on the top of the heat exchanger.

In the case of a tractor engine like yours, the normal path this air would take is up the top radiator hose and into the expansion area at the top of the radiator. Because you will have a built in air trap in the riser I would suggest a small hose fitting on the high spot and a hose that runs to another fitting in the expansion tank section of your heat exchanger.

This will constantly bleed a little bit of coolant and any trapped air out of the system. The hose can be as small as 1/4 inch, but it needs to have a constant rise from the engine to the expansion tank to avoid an air lock.


Bob England on TrawlerForum offered this: You are correct, those welds are magnificent. However, I would not have designed the raw water injection point inside the manifold. I know, stainless is very corrosion resistant, but seawater injected into a HOT exhaust stream is even more corrosive at the point of injection than the best stainless can handle.

That's why everyone else makes the "mixer" removable/replaceable. Also being inside the manifold, a leak will put saltwater into your cooling system.

I would build an external mixing elbow, preferably as high as the engine room allows. Insulate "lag" the dry up going side and water cool the down going side. Gerr's fine book has all the info.

Lagging is a "boaty" term for insulation, usually some type of fiberglass. Car hotrod guys call it "header wrap", just a heat resistant material that comes in rolls of various width. You wrap the dry parts with it then coat it with Childers insulation and lagging adhesive (looks like milk). Most NAPA stores near saltwater carry all this stuff, or can get it for you.


Eric on Willy (Willard Nomad 30) from TrawlerForum said: Well she's got the engine and if see'in is still beliv'in she's got the jacketed riser/cooler.

Janice I'd just use it as I think it will stabilize the temps of numerous things. Obviously you've got room for it.

But the mounting flange must be changed .. will-na work. A wire mesh type flexible exhaust coupling insert of probably 3" w flanges on both ends and then warped w heat resistant "blankets" would probably work but not exactly cheap. But not expensive either. Cheap would be just 4 90 degree elbows and longer vertical pipes.

I personally like the water jacket idea and perhaps a "V" shaped strut (or pair of same) could be fabricated super easy and attached to the transmission. That may keep the riser/cooler from parting company w the exhaust manifold. Vertical support will be easy but lateral could be iffy. That's why I mention the pair of struts as in a "V". What is the exhaust manifold made of?

My reply: The exhaust manifold is copper.

As for supporting that stainless riser/manifold, in addition to the two bolts at the engine, another bracket was mocked up that will support the middle portion of the unit. Next to me is a welder (steel shrimp boat) so he will torch cut the metal needed.

The stainless will be mounted to the engine so it will move in synch with the motor. Hoses will run between the heat exchanger and the unit, adding flexibility there.

And thanks for your advice and input. This is all new to me so having outside eyes is more helpful than you can imagine. Thank you Sir.


Another fellow from TrawlerForum states: It is the water jacketed exhaust manifold that dooms many DIY marinizers. It is a complex casting that just can't be duplicated in a one-off situation. The water jacketed manifold is the one item that makes a new Beta Marine engine cost twice as much as a new tractor Kubota.

The design of that stainless steel cooler is a disaster. All you need is a water injection elbow to do what that stainless cooler claims to do. The injection elbow was perfected many, many years ago for marine engines. It does need to be designed properly, installed with enough elevation and oriented so that the water flows downhill. There are many OEM and aftermarket injection elbows that can be bought relatively cheaply. The small Yanmar elbow costs about $500.

I would much rather see Janice use a keel cooler and a dry stack exhaust than that stainless contraption. But the lack of a jacketed exhaust manifold is the real killer.


More from Eric on M/V Willy: Here is my riser setup. Built by National Marine Exhaust in Marysville, WA for $750 in 2005. All SS and not water jacketed ... just water injected.

The green hose carries the spent seawater to the near top of the riser (fairly high) and the "T" at the bottom of the green hose is for water injection to the PSS shaft seal. 

The riser is mounted w 4 studs on the exhaust manifold. One of the studs can be seen and they are further apart that it looks. Re Vibration and mechanical security the outlet rubber hose to the lift muffler is quite stiff and my plastic (Poly Flex) engine mounts don't allow much engine movement even at idle. But not much engine vibration is felt on the boat.

I've never seen underneath the heat shield blanket so don't even really know what it looks like but it's very effective shielding the engine compartment and stray human parts from getting burned on the exhaust parts. The insulation on that red wire is completely intact and not damaged by the exhaust.

I was in Alaska when this was installed on Willy. I had no input re the design short of telling MM Exhaust about my boat. Everything was what they thought it should be. Don't know how I could improve on it after almost 10 years and 800 hrs of use. I had fairly constant trouble w the cast iron that was on my Yanmar (previous boat) and sought out a more trouble free riser. The typical cast iron risers are fine but require replacement close to once a year. They don't take much trouble to replace and clearly are the cheapest riser solution. Things get more complicated as the riser is built higher. 

So I submit the standard hardware usually employed for this mission is simple, direct, economical and effective. Any variations takes one into the world of experimentation. A place I'm fairly comfortable in to an extent few here would follow my trail. 

As I've said I kinda like your "riser/manifold" but re what some of the other more conservative guys have said there is definitely room for troublesome events or "miss-functions". Loosing your coolant or even catching fire probably won't happen and if anything resembling that happens you have good experience and seamanship to deal w whatever. 


Eric continues: At this point I see two very big problems. My suggestion of cross mounting and "V" struts will require very stout hardware and excellent mounting points. Success? Probably but maybe not. The other problem is metal expansion and contraction. The outside of the box will always be relatively cool but the internal pipes and 45s will be very much hotter. The box will want to grow in all directions but the pipe will grow lengthwise much more so. It will want to bust out at one end. Also the cool water injection pipe will be attached to the outer mass of metal (box) and the internal heavy and very hot pipe. Makes me wonder if there are any other weldments inside attaching the internal pipe to the outer box. If so there will be a great tug-o-war going on between the box and internal pipe. If not a lot of forces will be acting on the one thing holding (or trying to hold) the internal water injection pipe to the box.

Janice, Doug R's input seems very good to me. Read it again and see if anything comes to mind.

The subject of this article and more details on decisions, options and choices when transforming a tractor motor into an engine suitable for a boat are found in the next article. It is online now, and I solicit your opinions on this process. Thanks. J. 

The new article is:
Project Second Opinions

Is there anyone else who has put a tractor engine in a boat?
Are there any specific surprises I should be looking for, besides great fuel economy?!?

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