I think the DT466 motor I saw had a coolant filter. But my 1999 5.9L Cummins does not, and I doubt that yours does.
Now-A-Days, they make "universal" coolant that will work with red or green. Maybe you have that. It may look greenish-yellow, if I remember correctly. They make "coolant test tools" that are cheap that you can buy at any auto parts store. Little weighted balls in a tube that you fill with your coolant. If it passes the test, and the coolant is clear, not cloudy, and you see no rusty-looking or oily muck inside near/around the radiator cap, then your coolant will likely be fine.
If you see oily muck, beware. But with any muck, there may be more in the bottom of the radiator, and at that point, you will want to remove the radiator, turn it upside down, and flush it out; and also clean out the lower radiator hose; and perhaps flush the whole motor also, with the radiator and thermostat removed. Big job for some. Another day for others.
A bit of rust discoloration on the inner radiator cap can mean your heading to needing a flush sooner than later, or, not.
For some reason, I was thinking van cut-out. Likely your coolant "cap" is on a bottle above the motor. Look for muck or rust-silt in the bottom of the bottle, also - it will be less likely to be on the cap.