I completed flushing
the unknown green coolant from my Yanmar 3GM30F and replacing with Dexcool (pink). I used a radiator flush product and repeated with water until the flush was clear. This took an additional 4 cycles. What I did was (1) open filler cap on top of the heat exchanger
, (2) open two coolant drains, one on port side behind the alternator
and the other on the starboard side by the oil
dipstick, (3) let coolant drain (takes about 5 minutes), (4) remove water heater hose, blow coolant out of hose/heater, (5) close drains, (6) fill the heater hose with water and reconnect hose, (7) fill heat exchanger with a little over 1 gallon water, (8) run engine
till reaches temperature (180 degrees F), monitor
temperature gauge, run additional 10 minutes, verify water flow through heater by feeling temperature of hoses, (9) shut off engine
, let cool, (10) repeat. Along the way, I cleaned out the overflow bottle.
Although this process is not difficult, it is time consuming. Each cycle took about 3/4 hour, running the engine 10-15 minutes, letting cool 10-20 minutes, drain and refill. The challenging part was filling the water heater hoses to avoid an air blockage and so there'd be circulation.
To complete this will be motoring at high RPM, monitoring temperature and coolant levels. Now to consider changing fuel
filters and changing the oil!