Winterizing with antifreeze on block or not ?

[DOCDRS]

Marine antifreeze looses its protection dramatically if its diluted. Sucking it up into a non drained engine at idle will give you a false sense of security. Take a thermostat with a thermometer and put it into a pot of water on the stove. You will be surprised how little it opens at 160. Now you tell me how long its going to take to get all the water out of the block and diluted with the antifreeze? So if you use 5 gallons of antifreeze and you do manage to distribute it with all the water in the intake line, block, heater, exhaust manifold, muffler(yes , lots of water in the muffler-try draining it sometime)....you have diluted it in half or more.....your protection is greatly reduced and at idle pressures you are luck to have fully reached all the passageways in the block.....plus your spending 20 minutes of running the motor......why not just drain the block, and the intake lines then the antifreeze will go directly into your block and the dilution wont be as great.

Or you could run it for 20 plus minutes and check the specific gravity to determine the diluted burst protection......

A solution of -50 antifreeze diluted in half will only provide a burst protection of +15 deg F.