How to Change the Coolant in a Yanmar Marine Diesel

Updated April 17, 2017

Yanmar Marine manufactures marine diesel engines for sailboats and powerboats. Under normal operation, the engine's heat is removed by seawater pumped through a heat exchanger filled with antifreeze coolant. Yanmar recommends the coolant be changed every 500 hours of use. 6LP series engines should have their coolant serviced every 250 hours or every year, whichever occurs first. Yanmar also recommends that only purified or distilled water be mixed with the coolant

Access the engine by removing necessary panels and hatches.

Locate the engine coolant petcock drains. One drain is located on the bottom of the heat exchanger, while two drains sit on the engine block. Consult your engine owner's manual for the exact drain locations.

Place containers under each of the engine petcock drains. Use disposable aluminium baking pans, as you can bend and shape these containers to achieve the best fit.

Open the petcock drains. Capture the draining coolant in the aluminium pans. Adjust the position of the pans, if necessary.

Drain the overflow reservoir tank. The reservoir is plumbed to the heat exchanger tank. Use an old turkey baster to empty the reservoir tank.

Close all the petcock drains.

Service the engine with coolant. Pour the coolant into the heat exchanger until full. Fill the overflow reservoir tank to the level marked "cold."

Reinstall the heat exchanger's radiator cap.

Collect the old coolant from the aluminium catch pans. Recycle the coolant at your local recycling centre, or ask your vehicle mechanic to recycle the fluid for you.

Start the engine. Ensure that you have no fluid leaks. Add coolant to the overflow reservoir as needed.

Reinstall engine hatches and access panels.

Things You'll Need

  • 3 disposable aluminium baking pans
  • Turkey baster
  • Coolant
  • Distilled or purified water
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About the Author

Robert Osborne has written professionally since 2010. He writes for eHow, specializing in aircraft and boat maintenance, home renovation and electrical engineering. Osborne earned his Bachelor of Science in electrical engineering from George Washington University.