Understanding marine diesel engines: Yanmar coolant exchange

This video is a detailed demonstration of the fresh water cooling system of a salt water Yanmar diesel marine engine, including a description of repair principles and anticorrosion features to control galvanic reactions. The engine shown is a Yanmar 3GMFC engine with the SB20 sail drive. I show details of how to drain and refill/replace the antifreeze/coolant, and describe the layout of engine zincs present in some models.

This is an amateur presentation offered for free and in good faith, but with no guarantees as to accuracy or safety. Engine repair comes with inherent risks. Any misadventure you encounter if you decide to accept the risk of DIY repair is your responsibility.

[captnsquid]

Hi I was in Vancouver for 30 years from 1975 to 2005 I worked the distributors for Volvo Penta and Yanmar. Parts and Service and Warranties. I flew a desk and spare time rebuilt pumps and injectors. We use to run local service school on a weekends for our customers. Enjoyed the work and the companies were good to me. I enjoyed your explanations and service tips. Excellent and good job. Clean boat and well kept. Thanks for this video. I enjoyed it.

[martinandersson]

Nigel Calder's books on boat systems and maintenance are a great source, but your videos digest the same topics in such a nice format. I hope to see more videos in the future.

[lolosharko]

Thank you so much! 🙏 This video taught me so much more than the original manual did. I think you indirectly saved my 30 yo 3GM30F and potentially much more!

[ChrisThompson-dhmv]

Great video. You've got a great relaxed manner and you make sure that you don't use jargon or expect too much knowledge. I've read a fair bit about my Yanmar but you've given me a lot of valuable information I've missed. Many thanks.

[mpaul]

This is great info. I just bought a boat that is set up the same. My first month of ownership saw a $1, 800 maintenance bill for cleaning sludge from lack of proper preventative maintenance in the fresh water coolant side of my Yanmar. I won’t let that happen thanks to you

[jackdodsworth]

I've been a dinghy sailor my whole life, but I finally decided to buy my first big boat earlier this summer. I got in way over my head trying to understand and take care of the engine, but as a visual learner, your videos have been a godsend to get me up to speed on the basics. Thanks!

[billk]

Very well explained video Dave! Another reason for good maintenance on marine cooling systems is that it's all uphill for a boat engine. It never gets to just coast along.
Take care and thanks,
Bill

[juliogeorgiou]

Great video, thanks! On my yanmar, the overflow tank can easily slide up and off once you remove the cap, and you can empty it in the sink as well as rinse it out.

[namanjain]

This was very helpful. I"m rebuilding my 3HMF and at the end of connecting the hoses back but had no idea which is for what. I tried to follow the service manual and the parts manual for a while and just scratched my head. I watched your video and it was really to the point and perfectly explained. I went ahead and labeled all the hoses and what they are for. Thank you for making this video.

[jakesvharbourlights]

Thanks for the instruction and video. We've got 2 Yanmar 3YM30AE engines in our catamaran and I'm watching everything I can find on Yanmar marine maintenance. Thanks.

[patrickjames]

Great Video, excellent camera work and commentary, goes in-depth and covers crucial items glossed over by others.

[shayansartipi]

Thank you so much ! I have the same engine and your videos have really helped me get a better understanding of this type of system. I replaced the coolant, oil, oil filters and fuel filters based on your videos without any issues. However, most importantly, I am able to troubleshoot easier knowing how the whole system works. You are a good teacher ! Hope you continue to make videos like this.

[jeffmacmillan]

This explains a number of things that have taken me years to understand by trial and error. Keep posting !

[apackwestbound]

Great video, you are obviously knowledgeable and experienced. Thank you for putting together these instructional videos. I found your initial review tracing the raw and fresh water side passages through the engine helpful. It’s also great when you actually explain the various pieces we are looking at. For example I came across exactly the same two valve thermostat diagram in one of Nigel Calder’s books, but could not really “visualize” what was happening until you EXPLAINED the diagram. There is NOTHING I can say to improve your video-outstanding really and thank you again!

[garryn]

excellent descriptions. And the pauses to ask questions really makes me think and reinforces my understanding of what you are teaching me. Keep up the good works!

[goldenacres]

Thanks for this video. I had a Yanmar raw water cooled engine, so zincs were important and there was no heat exchanger. Now I am looking at a used boat with a fresh water cooled block and the associated heat exchanger. This video was a help in anticipating the differences,

[markturner]

Picked up a great tip on “the feel” test of the inlet and outlet pipes to/from the heat exchanger to confirm that the thermostat has opened. Thanks

[mickbanks]

These marine engine vids you have created are fantastic & so well appreciated as I move into dealing with a Yanmar 4JH

[SailingPivo]

Thanks for sharing! This is all new to us. I can't wait until we can do these things without any stress. Cheers

[thisradguy]

I am about to pull my very tired and underpowered SB8 for a solid running 2gm20f and this video definitely helped me understand the cooling systems and make me far less nervous. Thanks so much from a fellow Vancouverite 😊