Yanmar coolant replacement 3GM30F YEU query

[jrevkin]

I recently acquired an old Shannon 28 with a Yanmar 3GM30F YEU. The only access to refill the fresh water coolant is through the reservoir (see pic). There is a fitting where the pressure cap should be, that connects to the overflow reservoir.

Questions are as follows.

1) for this engine, are there 3 coolant drains, one on each side of the engine for fresh water and a third drain on port starboard side, for raw water coolant?

2) I have a bypass fresh water coolant loop to a 6 L Raritan hot water heater. The tubing from the heater to the fresh water pump has no drains or purge valves. How do I refill this enginge and purge air from the system and the loop to the water heater?

My thought would be to unscrew the fitting where the fresh water fill cap should be, to refill directly, though there is not much access to the top of the enginge, after draining out the coolant from the system and probably detaching the hoses to the hot water heater to empty the coolant from the water heater loop.

3) how do I refill the system and purge any air from it, given the absence of purge valves?

[Alan Mighty]

Originally Posted by jrevkin

3) how do I refill the system and purge any air from it, given the absence of purge valves?

Carefully and in stages.

Look on top of the heat exchanger (starboard side of the engine). Do you see a square section bronze bolt (most bolts have hex heads, this one is square)? Its bronze nature may be well disguised by paint.

So refill coolant (I like an Extended Life Coolant) in three or more steps.

First unscrew and remove that square section bronze bolt so it can act as an air vent.

Second refill slowly with that square-headed bolt removed, until coolant pushes its way out of that air vent. If you flip the compression levers, you can turn the engine over manually to help ensure that all air is out.

Third screw the square-headed plug bolt back in, and continue refilling.

Fourth run the engine a time or two to check that all air is out of the coolant ways.

Al