Not really a "cat" problem but I was helping my new neightbor put plugs in his rebuilder Cheby and when we got done he said the low coolant indicator kept coming on....well, I opened up the rad and a big glob of brown goo was on the cap and fairly well on top of the fins too..? Checked the oil, it looks ok, checked the trans fluid=good. It doesn't smell like trans or oil either...IDK is it just the gunk/crap from the PO not changing fluids then..? My guess is it needs flushed out really good and the level sensor (float..?) can't operate in that goo. I've seen buildup in rads before but not like that..? IDK Reminds me of that nasty "mineral" water well I drank out of in colorado one time! LOL Won't make that mistake again!