I'm finishing up replacing my head and was curious as to a way to flush the coolant passages out. I used a Scotchbrite pad to clean the deck surface and while I did block off the oil passages, I didn't with the coolant. I want to flush out as many of the micro-particles as possible, along with any gasket material.

Tell me if this would work:

Put on the head, torque it down, then with the t-stat housing off, pour water from a hose through that port, let it run through the head and block and out the waterpump port on the block.

 

The old-school method is to drain the radiator, then fill the system with cold water and run the engine just until it boils. Let it cool and repeat 2-3 times. Then do one last drain. Find out how much antifreeze the engine block itself holds. Add and equivalent amount of pure antifreeze to the radiator, then top it off with 50/50 mix. I definitely recommend only using BMW's brand, which has that dark turquoise color. It's $20/gallon, but remember one makes two when mixed 50/50.

 

The thing is I want to flush out the head and block before attaching the radiator/water pump/etc. I don't want to grit from the Scotchbrite to touch those and cause potential wear.

 

That's a tough one. You would have to look for some kind of drain plug on the block itself and open it up. Then pour water through each of the jacket holes from top so it flushes downward.

 

I ended up plugging the water pump port with a piece from a toilet and used a hose to fill the block with hot water through one of the jackets. I then used a shop-vac to suck it all out. Did that process a few times. I also sprayed the headbolt holes with brake cleaner and sucked it all up. Worked very well.

 

effective and cheap. It sucks that there is no good drain for the block.

Matt