I've looked up some of the information on flushing the cooling system but wanted to make sure I'm doing the best I can at home. I originally replaced my thermostat, flushed the system, and added a fan shroud after my '79 (351M) started to run hot. Long story short, I've now replaced the radiator, radiator hoses, thermostat (right one this time), and last night discovered there is a bunch of build-up in my water pump, so I'm replacing that and the thermostat housing (why not? ) Since I haven't completely put it back together, what can I do to flush the block (and where are the block plugs?) and try to get the system as clean as possible before connecting the new radiator?

The water pump looked like it had sand it (probably just buildup since it is likely factory). I didn't know if there was a way to flush a treatment through the block that would clean it without going through the new radiator, or do I need to hook the whole system up so I can circulate a treatment? What would be the best way to do that and which treatment is recommended? This is the first time I've turn down a cooling system, so I'm still in the learning process. Thanks!

 

I'm not sure on a 351M/400 but an FE has a block plug (square head plug, petcock, or allen-head plug) on each side of the engine.

..I pulled my FE a while back and while it was drained, I pulled the block plugs and nothing came out... then I poked the holes with a coat hanger wire and was greeted with a torrent of muck and scale.

..forward flush, back flush.... do the best you can.

 

Freeze plugs/knock out plugs are on the under side angled edge of the motor, look down by and BEHIND the motor mounts, easy to spot. 3 or 4 per side? Not the easiest to remove and replace with the motor installed. I believe it can be done, but what a PITA.

A coat hanger and some running water (garden hose) and dig dig dig to get all the settled junk out of the lower end water jacket areas. So I have read anyway.

 

Perfect, thank you! I was going to try and pull the plugs but I might not be able to get to them. I plan on just flushing the crap out of it when I pull the water pump, assuming I can get it off without killing myself (rusty bolts).

 

With the motor still installed, yes PITA. Keep in mind that some the water bolts (2?3) just go into the timing chain cove. So come reinstall time they do not get a ton of torque since the threads in that thin cover are easy to strip out.

I would use piece of cardboard to keep track of the pattern of the water pump bolt placement. Some are different length, if I remember right.

 

If you get those block plugs out or even if you don't you can use CLR or lime away to fill the block up and try to break crud loose. Use gloves and eye protection it is acidic. Be careful not to mix it too strong or leave it in too long because it will eat brass and aluminum and I am not sure what it would do to the gaskets. But it will help a bit. There are several discussions about doing this all over the internet. I have done it before with some noticeable results.

Take the thermostat out to do the flush with cold water and make sure the engine is cooled off first so you don't shock crack or warp anything.