Re: Drain locations on GM250 CID I6...
see attachment for location.
i use service manual #2. it basically states that i should drain all water for extended season use. ie. freezing night, nice daytime temps for boating. for winter layup, it says add anti freeze for extra corrosion protection.
i do the extended season thing. last year i gave up on the anti freeze for winter layup. i'd been emptying the water from the manifold, block, etc. and at very end of season removing the tstat and introducing pink anti freeze to the block and directly into the manifold via the ft. hose connection.
well, as far as i can tell. i get about the same amount of rust scale out of the manifold weather i use anti freeze or not. i always get some blockage, rust scale. so i guess i figured why bother with the anti freeze. it's just one more step, expense to do for winterizing. bondo's been stateing he uses air for winter lay up for years. no problems, no issues. i've become a believer. air just don't freeze. rust scale happens either way, why bother. waste of bread imho, + time.
fwiw. if ya got a raw water cooled engine. i don't believe you'll get any water out of the riser drain plug. i usually remove my big ft. hose to be sure the block is empty. i usually don't get any water out of it, but i wanna be sure. getting the water out of the cooling system is what's absolutely most important. after that it's your call..
edit. i use a folgers coffee can to catch the water when i drain my system. i get one full coffee can from the manifold. be sure to probe it with a wire probe of some kind. mine is always blocked by scale. the block i always get almost, but not quite three coffee cans of water and the block is drained. with the stupid petcock. ya can't probe it. this always worries me, but when i get my three coffee cans full, i believe i'm empty.
lastly, drain it with bow high. also drive full down. gravity will drain the drive.
