Draining Residual Cooling Water from Yanmar 1GM

[MHBsailor]

I visually located the circular knurled knob (serrated) at the top of the small metal drain pipe the drain hose attaches to, but it is too tight to loosen by hand. I am reluctant to apply pliers to the knurled knob as I don't want to damage the serrations. There seems to be a notch for a flathead screwdriver within the inner circumference of the knob, but I can't get far enough into the engine compartment in to see what size of screwdriver blade it takes and I don't want to strip it. Does anyone with a 1GM have any tricks for loosening this knob so that the remaining cooling water can be drained from the cylinder head? Thanks! JD

[Frenchy]

Sorry, I can't help with info about draining the 1GM. When I owned one, I removed the thermostat, replaced the cover
and put the water intake hose into a bucket of fresh water, then pink antifreeze. After about 5 gallons of antifreeze went
through the engine, I would shut it down and change the oil.
I've heard that draining the water jackets actually increases rust formation. The antifreeze has anti-rust properties.
Good luck - Jean

[MHBsailor]

Thanks Jean. I agree about the anti-corrosion benefits of proper marine antifreeze for winterization of the diesel engine. However, in this case this is only a temporary action before professional winterization. I went back to the boat today and was able to loosen the plug by getting a better angle on it with pliers. Turned out the whole thing was plastic.