Repowering with a Tractor Motor

[janice142]

I'm in the process of repowering, using an inexpensive 18hp Kubota tractor engine in my trawler. Marinizing the cooling system is the latest piece published in the series about the process. If this subject interests you, the article is here:

Janice142 article Marinizing the Cooling System of a Tractor

[DougR]

Hello janice142,

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.

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.

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 dissappear 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

[janice142]

Thank you Doug. There's a lot to understand about the system and I'm still learning. Yes, riser is another term. It will be supported too by more than the two bolts at the engine. Even empty it's heavy.

It's a boat, right? All was designed, built and arrived at the engine where we discovered with the engine back and on her motor mounts, the doggone thing didn't fit. Argh.

So, move engine forward, install a flex plate and voila: the extra ONE INCH we needed was found.

As you pointed out, it's too heavy, (even empty this is not a light unit) so will be supported by brackets.

The heat exchanger too is having it's own bracket built. Fortunately I've got tons of room in the engine room so the exchanger will go against the forward bulkhead. I'd thought about making it a heat source for in the winter but at this point just want the job done.

Heat can come later. I've seen heat exchangers used as heating sources in small boats. That's a Later (much later) item though. And I'm all too aware of job-creep. It's costly!

I'll check on the opening at the top of the riser too... The heat exchanger will be above but as you rightly point out, that riser needs to be filled with fluid to do it's job.

Lots of great information in your post. I appreciate that.