1993 Ranger valve clicking noise

I recently purchased a 1993 Ford Ranger extended cab. I noticed when I bought it that there was a clicking noise coming from the engine like the valves were clicking as though low on oil. It will click for about 10 to 20 seconds then quiet down to normal sounding then start clicking again. It also does it when going down the road. It currently has 163K miles on it. It does not leak oil and the previous owner had copies of all repairs done, including transmission fluid flushes, replaceing engine head gaskets, brakes, etc. It has no loss of power, but does seem to burn some oil, having to add one quart within th 3K miles oil changes. I have added both Slick 50 and Lucas oil additive to try to quiet the valve clicking to no avail. I also have noticed that the engine temp gauge goes up just very slightly once it is warmed up, just past the cold line, no matter how hard or how long I drive it. What could the clicking be? I was told by a friend that it could be the idler