Yanmar repair

[ChrisA]

Can anyone recommend a competent Yanmar mechanic? I have a 3GM30F that is mysteriously loosing fresh water coolant.

[PrisSail]

Chris' post is old enough maybe his problem is solved by now ... but taking care of your heat exchanger is easy if you do it regularly, just like changing your oil and coolant.  You should remove the tube stack every two years and wash out the tubes using a little bottle brush.  Often you will find little bits stuck on the ends of the tube stack that impede the flow and can cause overheating - impeller bits, grass, and gawd only knows how some of the stuff I find makes it past the raw water strainer.

Chris: Since you said "mysteriously" I'm assuming you don't have white exhaust smoke, so your tube stack probably has a leak.  Yanmars are super easy to work on.

There are little drain valves (or cocks on old engines) here and there around your engine, probably six, each *should* have a short length of hose on it, half of them drain out the raw water from the cooling system and the other half drain the coolant.

Start with the one under your fresh water pump since it is so obvious, there won't be a hose since it is near the belt.  Put a cup under the valve and open it, you will need a wrench or pliers.  Only a few drops will come out.
When you have the valve working close it and open the coolant cap on the heat exchanger.
Put the cup under valve/cock and open the valve again, the coolant will drain quickly.  If not, your valve is clogged with crap, recap the heat exchanger, unscrew the valve "handle" and poke the gunk through the valve with a wire, toothpick....

If that valve is below the level of the heat exchanger then that's all you need to drain, if not find another valve and drain some more.  Or drain it all and renew the coolant.
Drain the raw water using the other set of valves.
Remove whatever hoses are in the way of the heat exchanger, then remove both caps from the ends of the heat exchanger.

Hey, it is so easy even a girl can do it!

Get a piece of wood that will cover as much of the end of the tube stack as possible and VERY GENTLY hammer on it, you will likely have to go back and forth on both sides.  Those copper tubes are soft, don't smash them!
If you get it out and can find the hole I don't know if they are repairable, there is a decent Yanmar parts place on Anders (past Boaters Resale) you can ask them and get a new one there.
If there is no hole clean it up and reassemble everything and call for help.  For your first time going slow it shouldn't take more than two hours.

If you can't get it out I think the entire heat exchanger needs to be removed and soaked in a mild acid solution ... probably worth paying someone to do that.

I do all my own boat work so I haven't used this guy but do like him as a person, and haven't heard anything bad about his work:
Capt. Buck Beasley
Pro Yacht, at Seabrook Shipyard
TexasProYacht.com
281-216-1619