Flushing Coolant

[SeaRenity]

Does anyone have experience with changing antifreeze ( or flushing) closed coolant.
Where do you drain coolant? Do you add any flushing chemicals?
350 Mag Horizons
Thanks
Rich

 

[northern]

Not a 350. I pull the hose off the bottom of water pump and let it drain. Fill engine with fresh water, warm engine, drain and repeat process until all anti freeze is gone then fill with 100% anti freeze to give me a 50/50 mix. Do not use any chemicals. Take waste anti freeze to local waste recycling place and they accept it in large anti freeze barrel. Make sure your bilge is clean and you do not pump any into the water.

 

[btyman11]

I just changed on my 8.1 yesterday. There were 2 plugs towards the rear of the motor. 18mm socket on mine. I let coolant drain right into the bilge. My boat is still on land so it drained out the drain plug hole into a pan. Sucked up excess with a wet vac. Replaced with pre mixed Merc coolant. Approx 5 gals in my 8.1s. Easy peasy. Hardest part was replacing plugs as they are hard to fine and not alot of room to work on my 02' 340.

 

[paulswagelock]

Use the block drains as mentioned. If it comes out relatively clean, no need to flush. If rusty or contaminated, fill with water, run the engine and drain.

 

[rondds]

I pulled the lowest hose I could find and caught the drainage in a large shop-vac. No need to make a mess out of the bilge. Also allows you to measure how much you got out (pour the drainage into empty containers of known capacity). I think the capacity on an 8.1 is 20 quarts (sorry, I forget exactly). But whatever it was I got 90% out. No flush. Just replaced with the same color new stuff (red/orange).