And here is the story. Early this summer I discovered that I had the "gray sludge" in my radiator. I flushed the engine. I used Prestone cleaner, back flushing tee, yada yada yada. Doing so did not clean the sludge out of the radiator. So I pulled the radiator, took it to a commercial radiator shop, and they pressure flushed the radiator. The sludge is kind of like clay, and with enough force, can be cleaned out. It is not at all scaly or crusty like typical cooling system corrosion.
Anyway, a month ago I checked the radiator again and there was more sludge evident. Not near as bad as before, but still there nonetheless. Actually, I guess, moretheless. So there are two possibilities: 1) more sludge is forming even as you are reading this posting and man, I sure hope not! Or 2) Pre-existing sludge elsewhere in the engine is still moving around and accumulating in the radiator; this I consider very likely, as it took a lot of water and pressure for the shop to clean out the radiator.
I wanted to ensure that after I clean the radiator one more time, it does not get clogged up again. So what you are looking at is a bypass coolant filter. The feed tees into the heater line on top of the block. The outlet tees into the heater return where the rear heater return line connects to the front heater return line on the firewall next to the back of the engine. The filter is specifically for filtering coolant and is typically used on big rig engines (think semi trailer).
I don't look forward to pulling the radiator again and hope this is the last time I have to do so for quite some time.
Assuming #1, wouldn't the sludge still accumulate in the heater core and the radiator with some, but only a fraction, passing through and being trapped in this filter... but unless you put the filter between the block and the radiator I don't understand how it would clean up all the sludge.
Assuming #2, then do you have any ideas what caused the sludge to start forming or why it continues to build up?
Please keep us posted on what you find in the filter each time you check or change it. This is interesting...