R21-EC Fresh Water Flush - Please Help

[Boris the Tug]

I want to completely flush the fresh water on my 3YM30. I’ve read the manual and some posts on here already but still not entirely sure of the best way to go about it.

1 - The manual on page 53 (33R1) says to “Open the two cocks for fresh water and extract the fresh water“. I assume they mean the “drain plug for coolant” on the port side and the “drain cock for coolant” on the starboard side as shown in the illustrations on that same page. What’s the best way to drain from these two places and what tools should I use? That port side one has my stumped.

2- Once drained, I want to flush it out as best as possible. I’ve read on here to fill SLOWLY with water (soft, or distilled) or even antifreeze (the pink stuff), run the engine for a bit, and then drain out again. Do this a few times. Does that sound about right? If not how do you do it?

3- After done flushing, time to fill it up. It’s not clear to me how much water to add versus how much coolant. From the manual (which is very confusing sometimes) it sounds like only water (no coolant) up top in the filler cap until full. And then add coolant to the coolant recovery tank to the low or high level mark. Is that right?

I’d appreciate any help on this. I bought the boat used a couple years ago and have no idea how the previous owners treated it, so I’m doing my due diligence to keep it ship shape moving forward. Thank you.

 

[bob daily]

Boris
Sent you a text, if you have any questions let me know, good luck

 

[Capt’nKarl]

What exactly do you mean by “fresh water flush”? Are you trying to flush the coolant from the closed system with antifreeze or trying to flush the raw water system?
Karl

 

[bob daily]

Boris was flushing the antifreeze, closed system, hopefully he will post and let us know how it went.

 

[Boris the Tug]

Good question Karl. I meant the coolant, as Bob mentioned. Bobs been a big help!

That’s my point about the manual. They use the words “fresh water”, “coolant”, and “cooling water” interchangeably :roll:

I did figure out the port side drain plug, it comes out with a 3mm Allen wrench. No coolant or water came out of it though.

Im going to drain from the Starboard side drain cock (the one on the engine block) and then flush a few times with water. Then fill it with about 5 quarts of Prestone DexCool 50/50 (orange). I found a good list of coolants from the Yanmar Bulletin on page 4.

Any tips to add?

Its been raining here this weekend so haven’t gotten a chance to do anything. Heard it might even snow in the mountains here in Northern California!!

 

[Boris the Tug]

To close the loop here, the flush went great. I found out there is a bleeding port by the water pump, and if you remove it while filling, you will ensure no airlock. When the coolant starts coming out of the port, screw it back on and top off with coolant at the fill port.