Just thought I'd share my experience today with the coolant overflow tank. I noticed that it was nearly empty, and the radiator was low. At first I thought about thaoe infernal plastic elbows, but wifey, who is expert at nitpicking (picks the smallest nits ) and closely examing everything looking for probles and faults (especially if it's my fault . . . .) saw wetness on the overflow-tank-to-radiator hose. The hose had gotten itself up against a belt or pully and had a hole worn into it. I decided it would be easier to remove the tank in order to replace the hose, and upon removing the tank I discovered that there was no way a person could see through it, as there was this god-awful dark goo lining the innards of said tank . SO I decided to clean it. I rinsed it out with a water hose, and the crap didn't budge . I thought, I'd just let it soak for a while so I pluged it up and filled it with a strong solution of TSP and let it sit for an hour. No joy after checking it, the grunge ate the TSP I reckon. SO I added some lye and let it sit again. Looked in there, and lo & behold, the garbage kicked lye's butt Huh? This stuff must be toxic waste! I took a dowel rod and covered the end with taped-on foam rubber, and tried to scrub on it. I just smeared it around. I got some on my hands, and it was nearly black. Looked and felt like old Moly grease. Took some engine cleaner, and Yay! engine cleaner cuts it! Man, what could it be?