I think you could use a laser temp probe to read the temp of the radiator at many points on the radiator core to determine if there are cool spots or hot spots. That could show where water is not flowing and whether the radiator needs rodded out or new core soldered in. I pulled my radiator out and had it cleaned and rodded and soldered to fix a small leak. It was a bit of a bear to remove so I replaced the water pump and all the hoses plus belts because I wouldn't want to do this again anytime soon. I seem to only get a year out of a fan clutch and I can't figure out why. I tried a four season clutch from napa and another one from autozone. This year I bought a ac/delco so we will see. I would like to pull the fan and check its balance but it looks like it won't come out unless I remove the shroud and I ain't pulling the grill again to do that.