Pete the Cat
Member III
It's no secret that the primary challenge of maintaining marine engines is the raw cooling systems. Since many, maybe most, recreational diesels are engines adapted from tractors and land-based usage, the cooling systems are often cobbled together with a collection of aftermarket pumps, fittings, heat exchangers, and exhaust elbows by folks like Westerbeke/Universal, Beta, and others. These systems combine heat, salt water, dissimilar metals, and high pressure to create a hostile environment for all the components. I thought it might save some grief to lay out some basic observations based on my experience with these systems. So FWIW, here we go:
1. Sea strainer?? Do I need one?? I think you will find that on the big diesels of fishing boats and trawlers with large engines, a sea strainer is always part of the system. When you get below 40 hp the designers seem to think a screen on the outside of the hull will keep out the big stuff (remember to antifoul the inside of that screen) and that the pump will grind up the goo that gets beyond the exterior screen. I have Vetus strainers on my boats for years and would mostly agree that going "strainerless" is probably OK unless your boat lives in a particularly gunky area--my strainers have never picked up a lot of gunk that could not be chopped fine and sent through the system. I still think a sea strainer is a good idea, however and can prevent future problems if you do not regularly take your system apart for inspection and maintenance. That ground up gunk will eventually foul your heat exchanger or exhaust elbow injection site after some hundreds or maybe thousand hours. It does not take much gunk to compromise the flow of the 3/8" ID raw water hoses on most small diesels. So do you need a strainer? Probably not if you monitor everything closely. But if you want to avoid surprises, I think they are a good idea.
2. My raw pump is leaking, what do I do?-- There are a lot of Youtube videos about fixing raw pumps, but not about diagnosing system failures. If your raw pump is leaking it could be from a variety of issues: could be the bearings or seals are shot, but it also could be that something is blocking the flow in the hoses, heat exchanger or exhaust elbow and creating more pressure inside the pump than the seals can retain. Most raw pumps like the Oberdorfers or Sherwood pumps can be rebuilt easily by anyone with a few hand tools and a repair kit. The seals need to be installed in a particular orientation, but it is simple task (there are Youtube videos, but Oberdorfer has taken down their very good repair videos for some reason). But a leaking pump may not be solved by rebuilding the pump if the problem is back pressure in the system--see below.
3. Hoses and heat exchanger problems, oh my!--I think it is good practice to take the entire raw water system apart periodically to inspect it for broken impeller blades (find them!), clogged heat exchangers (you can clean them yourself) and exhaust elbows (check the water injection sites as well as carbon buildup) as this is where crud can clog and create back up pressure and inadequate flow in the system. Back pressure can lead to pumps and heat exchangers leaking, when they are fine.
I am not a youtuber nor a competent videographer, but I do have photos of the various maintenance processes (rebuilding pumps, cleaning heat exchangers) if anyone is interested. My point here is that many (most?) problems with small yacht engines seem to start with the raw cooling systems, their general poor design (Yanmar, Volvo and some others are integrated systems and work better than cobbled tractor systems IMHO), and lack of maintenance. It is a PIA to take them apart, but I think most cruisers would benefit from going through their systems periodically while at the dock and near parts resources to avoid having something unpleasant occur when in an anchorage. I carry a replacement raw and fresh pump with me at all times and have had to change them out more than once while on a cruise in my decades of cruising.
Just some ideas collected from some years of trying to live with small marine engines. FWIW.
1. Sea strainer?? Do I need one?? I think you will find that on the big diesels of fishing boats and trawlers with large engines, a sea strainer is always part of the system. When you get below 40 hp the designers seem to think a screen on the outside of the hull will keep out the big stuff (remember to antifoul the inside of that screen) and that the pump will grind up the goo that gets beyond the exterior screen. I have Vetus strainers on my boats for years and would mostly agree that going "strainerless" is probably OK unless your boat lives in a particularly gunky area--my strainers have never picked up a lot of gunk that could not be chopped fine and sent through the system. I still think a sea strainer is a good idea, however and can prevent future problems if you do not regularly take your system apart for inspection and maintenance. That ground up gunk will eventually foul your heat exchanger or exhaust elbow injection site after some hundreds or maybe thousand hours. It does not take much gunk to compromise the flow of the 3/8" ID raw water hoses on most small diesels. So do you need a strainer? Probably not if you monitor everything closely. But if you want to avoid surprises, I think they are a good idea.
2. My raw pump is leaking, what do I do?-- There are a lot of Youtube videos about fixing raw pumps, but not about diagnosing system failures. If your raw pump is leaking it could be from a variety of issues: could be the bearings or seals are shot, but it also could be that something is blocking the flow in the hoses, heat exchanger or exhaust elbow and creating more pressure inside the pump than the seals can retain. Most raw pumps like the Oberdorfers or Sherwood pumps can be rebuilt easily by anyone with a few hand tools and a repair kit. The seals need to be installed in a particular orientation, but it is simple task (there are Youtube videos, but Oberdorfer has taken down their very good repair videos for some reason). But a leaking pump may not be solved by rebuilding the pump if the problem is back pressure in the system--see below.
3. Hoses and heat exchanger problems, oh my!--I think it is good practice to take the entire raw water system apart periodically to inspect it for broken impeller blades (find them!), clogged heat exchangers (you can clean them yourself) and exhaust elbows (check the water injection sites as well as carbon buildup) as this is where crud can clog and create back up pressure and inadequate flow in the system. Back pressure can lead to pumps and heat exchangers leaking, when they are fine.
I am not a youtuber nor a competent videographer, but I do have photos of the various maintenance processes (rebuilding pumps, cleaning heat exchangers) if anyone is interested. My point here is that many (most?) problems with small yacht engines seem to start with the raw cooling systems, their general poor design (Yanmar, Volvo and some others are integrated systems and work better than cobbled tractor systems IMHO), and lack of maintenance. It is a PIA to take them apart, but I think most cruisers would benefit from going through their systems periodically while at the dock and near parts resources to avoid having something unpleasant occur when in an anchorage. I carry a replacement raw and fresh pump with me at all times and have had to change them out more than once while on a cruise in my decades of cruising.
Just some ideas collected from some years of trying to live with small marine engines. FWIW.