Cleaning Yanmar 3YM30 Heat Exchangers

Two engines means two chances to get it right. Or to screw it up…

Clip the zip tie holding the coolant hose

Remove the alternator belt guard

Remove the lower bolt from the back side of the alternator

Loosen both the front and back bolt holding the alternator

Remove the alternator belt

Remove the alternator cables

Zip tie the alternator up to get access to the heat exchanger

Place a bucket under the rear coolant line, where it exits the heat exchanger

Unscrew the hose clamps and remove the rear hose letting the coolant drain

Close the raw water thru-hull (on the saildrive)

Remove Raw water hose clamp

Loosen the Raw water hose clamps and remove the raw water hose
Remove the three Allen head bolts that hold the cover on the heat exchanger

Remove the o-ring on the heat exchanger

Unbolt the Exhaust Mixing Elbow (four bolts)
Rest the Elbow out of the way
Remove the three Allen head bolts that hold the rear cover on the heat exchanger
Using a block of wood and a rubber mallet, gently tap the heat exchanger from the FRONT

Place the Heat Exchanger in a container and soak in CLR

The scrub the Heat Exchanger and use a brush to clean the tubes under clean water.
Soak hoses in CLR until they stop bubbling and rise with plenty of water.

Treat any corrosion – sandpaper down to bare metal, wipe with acetone, primer paint, and finally engine paint. Wait 24 hours between each step.

Primed and ready for engine paint

There are 4 o-rings for the heat exchanger. Best to use new o-rings and coat with Sil-Glyde lubricant.

Be sure to use a new exhaust mixing elbow gasket and use a razor blade to clear off the old gasket material on both the elbow and the heat exchanger.

Reassemble in the opposite order
Fill the coolant with AC Delco Cool Dex and distilled water (4.6L)

Check those hose clamps. Stainless or not they can fail.

I took my time, didn’t rush, and this job took about 6 hours start to finish per engine (excluding waiting for paint to dry…).

Now I have a nice clean engine, ready for many more hours of happy operation!


  • jim hanson February 17, 2017 at 1:27 pm

    was this preventative maintenance? or did you loss cooling?

    Jim Hanson
    s/v Imagine
    Seawind 1160, Hull #34

    ps. love this web site, just found it

    • Chris French February 18, 2017 at 9:44 am

      Jim, really appreciate the praise, thank you. It was more preventative maintenance. However, it seemed like there was a bit of steam in the exhaust so I was concerned. I did however notice a slightly increase amount of water after cleaning them.

  • Steve Gill March 9, 2018 at 11:26 am

    Hello Chris,
    I had a total blockage in my cooling system on my 3MY30 with only 200 hours on it over 4 years. I started with the heat exchanger. It was the first time for me doing this. Your step by step guide with fantastic photos was an invaluable help. As it turned out the heat exchanger was pretty clean (did clean it though) but I had to replace the exhaust elbow. For that, I took it to a shop as I do not have a torch and a vise to take it apart from the mount. . All is well now and I have more water than I have had for some time. I was fortunate as I just had finished motoring up to Ventura, CA from Ensenada Mexico with no issues. My 3My30 is in a 1980 Bristol 35.5 (fixed Keel). Thanks you did a great job on you article A+.

    • Chris French March 9, 2018 at 1:52 pm

      Steve, I’m very happy that my post was helpful! And that you made it to Ventura.


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