Coolant flush advice

[Michael Rogge]

I noticed that my truck ('93, 4.0 OHV, manual) didn't really want to come up to temperature, figured it must be that the thermostat is stuck open. Got a new thermostat and coolant and went to drain the system. I opened the drain valve on the radiator and nothing came out (yes, I did remember to open the radiator cap to let air in). Turns out there is so much sludge at the bottom of the radiator that it won't drain, even after spending an hour removing the 3 tablespoons of sludge that could be reached with a dental pick and the end of a broken ziptie. The previous owner claimed to have replaced the radiator, and I believe this as the fan shroud is missing, but the replacement may have come from an equally abused junkyard Ranger. The engine overheats when it's hot out or when the AC is on, which I though was due to the lack of fan shroud, but is probably the clogged radiator in hindsight.
It seems based on this that a coolant system flush is in order, as I suspect the engine's coolant passages are almost as bad. Where (if there is one) is the drain plug on the block on a 4.0 OHV, and what procedures/products have you guys had the best results with getting the gunk out?

 

[franklin2]

I had the exact same problem with my 2.9. So much sludge the water would not come out of the radiator drain.

So I took off the lower radiator hose, and took a garden hose and cleaned it all out. Put it back together and what did I get? More sludge.

So I took the radiator hoses off again, and also took the heater core hose off the engine block. Using the garden hose I kept flushing till it was clear. Put it back together again, but with water only. Drove it a couple of days, then drained it again, more sludge. Flushed it with the garden hose, filled it again with water, repeat. I finally got it where it stopped sludging up the radiator by just running it with water and then draining it. I finally could put some anti-freeze back in it.

Then guess what happened? The freeze plugs started leaking. Had one on each side. Tried the rubber freeze plugs, but the block cavity is so shallow they would not stay in. Finally had to take the engine out, glad I did because there is a freeze plug behind the bellhousing area that was weeping.

Replaced all the freeze plugs, changed all the gaskets, timing chain, checked the bearings, all looked good. Put it back together and it has been running for years now. I did find a crack in one of the heads when doing all this, so I got some new heads for it also at that time.

 

[Michael Rogge]

My water is very hard here, will the calcium cause scaling if I use a garden hose?

 

[franklin2]

Once you see the state of the cooling system that it is in now, you realize a little hard water briefly run in the system does not make much difference. The advantage is you can run plenty of water through it to flush it out, and just let it out on the ground when flushing and changing it. Anti-freeze as you know is expensive. I would not use it with distilled water till the end when it's finally cleaned out.

Eyeball your radiator when you drain it, if it has a lot of white stuff in it already, then you probably need a new one.