2003 Toyota 4Runner 1GR-FE engine (4.0 l V6) losing coolant very slowly. I had to top it off last summer when I noticed the temp gauge starting to climb while stopped at a light. Just filled it again this morning, maybe a couple of quarts at most. I have 126k on this engine and have not replaced the water pump.

 

Could be a small leak in the old waterpump (happened on my old 3rd gen). Or a leaky headgasket

 

Or, a leaky radiator, radiator hose, heater hose, coolant overflow tank.....lots of places to start looking.