Cooling system maintenance is crucial to longevity of your diesel engine. Aside from changing the water pump impeller and coolant as recommended by Yanmar, cleaning of marine growth, mud, and mineral scaling build up in the raw water components of the cooling system is necessary on a periodic basis. Many owners will opt for running some descaler through the system and hope that all is well. Depending on what agent is used as a descaler, varied results are achieved and possible damage to components from corrosive solutions is possible. The best way to confirm the cooling system is up to the task, is to disassemble it and thoroughly inspect all components. This way in addition to visual inspection of the various parts, hoses and seals can be replaced as a preventative measure.


There are five major parts that should be removed and inspected:

  • Heat Exchanger
  • Transmission Cooler
  • Oil Cooler
  • Turbo Intercooler
  • Exhaust Elbow


In addition to those items, the exhaust manifold should also be inspected. There is a service bulletin on the effects of cavitation of the aluminum exhaust manifold, which should be considered at this time while everything else is apart. If there is a weak spot in the design of this engine, it is the use of aluminum in the exhaust manifold.


Stella Blue had about a thousand hours and eleven years of service when I decided to perform this service. I noticed this past season, when I would do a periodic WOT run to check WOT RPM's, the engine coolant temperature would climb about 10 degrees higher than was normal. I figured a good cleaning was in order. What follows are the basic steps I took. On this page I will discuss the overall process and links to individual component cleaning and inspection. By doing this PM now, I hope to enjoy another ten years of trouble free cruising.


First thing I notice when removing the parts is none of the engine side of the parts are painted. I guess they paint the engine and coolers after everything is assembled, which leaves bare copper surfaces to turn green (formation of basic copper carbonate) when exposed to oxygen (mainly dissolved in water.) This makes a mess as the powdery residue falls on other engine parts. I plan to finish painting the components before reinstalling. Spray cans of Yanmar Grey are available from Toad Marine supply: manufacturer: MBP, part number : MBP317, description : Yanmar Grey Engine Paint - 12 oz can.


Heat exchanger with seepage at end cap seal causing copper carbonate residue.  



All the coolers used on this engine are built by Monitor Products, Inc. 15400 Flight Path Drive, Brooksville, FL 34604.

Below is the engine side of the oil cooler showing bare copper surfaces as well.

The intercooler below was a little oily on the inlet side. That will clean easily in solvent degreaser.


The exhaust elbow looked to be in very good shape inside and out.

It really isn't very difficult to disassemble these components from the engine except for the hoses that tend to stick on the barbs or fittings. The parts are relatively easy to clean. I will discuss the cleaning and inspection of each component in its own article.