Cleaning water passages?

I'm throwing a 350 in my '55 while I take my time with rebuilding the 265. The 350 is in great condition. I'm pulling it out of a '72 C-10 that ran when parked almost a decade ago. Oil pressure shot right up with my primer and all the cylinders were very close in cranking compression. I'm only swapping the short block. My only concern is that the cooling passages may be pretty dirty. When I pulled the rad hoses a ton of red dust poured out of them. More than a handful. I doubt that much rust settled in the cooling system, I think it's probably the dried remains of Bar's Leaks or somthing similar. My radiator will be fresh out of the shop and I would hate to clog it up because of a temporary donor motor swap. Besides cramming my block brushes as deep as possible and flowing some water through the passages, is there any magic chemical that will help loosen up some crap in the block? Freeze plugs are cheap but can be a pain. If pulling them will make things a lot easier it's fine but I would hate to break the seal unless I have to.

 

Get a power washer and stick it in every water orfice you can find. Might want to remove the water pump (gaskets are cheap) and do the same there.

 

Quote: Freeze plugs are cheap but can be a pain. If pulling them will make things a lot easier it's fine but I would hate to break the seal unless I have to.


The freeze plugs are probably about rusted out anyway! Remove them and really get in there and really flush the block. It is amazing how much cooler the engine will run with clean water passages! <!-- / message --><!-- sig -->

 

Maybe some sort of acid would help? I pulled the plugs today and its pretty clogged in there.

 

Even after a thourough acid dip for both the block & heads I always still find dry rusty particles/silt in the water passages. Grab an air nozzle and keep rotating what your cleaning out. Never had a problem yet.

 

Prestone makes a chemical flush. You can find it at most parts houses. Follow the directions to the T. It has worked good for me in the past.

 

Get a welding rod and sharpen the end then shove it in there anywhere you can especially down at the bottoms of the water jackets where the sediment tnds to pack down. You'll be surprised how much gunch comes pouring out of there when you get the hose going through the water neck. DOn't forget the block drain plugs on the sides...careful though.
Afterwards, tape the hose to the lower hose tightly and do it again while that nasty comes out the water neck again.