Possible head gasket symptoms.

"To find out for certain if you have a head gasket problem do a leakdown test this video shows an excelent video for this

https://www.youtube.com/watch?v=WgrfT0LF...

Some other things to look for that may cause the the lose of fluids , check the heater core inside the car . look for a wet floor on the passenger side , look for steel coolant lines that may be full of small pinholes from rust . they will release coolant as steam and you wont see any sign of the lose. you can also check for heater hose pinhole that could be dripping directly onto the exhaust and therefore no sign of lose ans it is turned to steam . Check the system cold with pressure . Look at the seams on the rad for moisture . Then run the system up to op temp shut the truck down and then pump up the pressure . This is done with a pressure test pump . Check your PCV valve is working properly . Check the intake manifold for leaks this usually happens in the intake valley under the throttle body . Just some ideas Hope they help"

@parzival possible but unlikely. You would see at least one of the symptoms you described. Check your cooling system and preform a pressure check on it. See if there is a leak somewhere. Let us know what year,make and model your truck is.