I bought my truck used at 110,000 miles. I havent had any trouble with it to date at 165,000 miles, but I have reason to suspect that my head gasket had already went and was repaired before I bought the truck.
The radiator was new when I bought it, but had a leak at one of the end caps. It ended up plugging up with oil/ water emulsification less then a year later and I became concerned. While changing the radiator and thermostat I also saw a buildup of the chocolate milkshake in the thermostat housing. I put everything back together and bought a test when I got off of work a few days later. The test done several times didn't show any combustion gas in the coolant. I flushed the system and refilled and a few months later flushed again and didn't see anymore of the buildup anywhere. Also the truck had new plugs in it. I kept an eye on it for a while and all seems to be well.
The only thing I can conclude from that is that the gasket had already been repaired prior to the PO selling or trading the truck, unless he mistakenly dumped a quart of oil in the radiator lol.
