Loss of coolant

Check the hose going to the expansion tank, That it is not pluged up.

not the pump but air in the system or a broken wire to the coolant level sensor
that sensor at the top of the radiator tank has to be completely immersed in coolant or the circuit is broken and the light comes on
same effect id the wire to that sensor is broken in the insulation

If you are saying that it comes on now and then, and goes off, your may just need to add Anti-freeze/boil to the overflow tank. Does it come on when you're coming to a stop or going up or down a hill, if yes, add coolant to the overflow tank to bring it up to the correct level, not the radiator.

A small loss over a long period of time is acceptable, but constant refilling, indicates a leak either internally, with the coolant exiting through the exhaust, or one that you should see under your car occasionally. Sometimes you'll find your coolant leak in the floorboards if the heater core or hose leaks.

If your sensor comes on after driving a while & goes off as a result of adding coolant, then you'll probably need to pressure test the cooling system to identify where the coolant is going. Bad hose, seal, headgasket, head, etc.

FILL COOLANT SYSTEM UP BY POURING COOLANT IN THE EXPANSION TANK UNTIL COOLANT LEVEL STOP DROPPING IN THE EXPANSION.WHEN YOU POUR COOLANT IN EXPANSION TANK AIR BLEED OFF THROUGH THE SMALL COOLANT LINES GOING TO EXPANSION TANK.WITH PRESSURE CAP OFF RADIATOR COOLANT LEVEL IN EXPANSION IS AT FULL COLD MARK.WHAT YOU TO DO CRANK ENGINE UP LET IDLE WARM UP UNTIL COOLANT DROPS IN EXPANSION TANK KEEP ADDING COOLANT UNTIL STOP DROPPING STAY AT FULL COLD MARK.WHEN COOLANT LEVEL START RISING IN EXPANSION TANK.PUT PRESSURE CAP BACK ON RADIATOR.WHILE ENGINE IDLING WATCH TEMPERATURE GAUGE.IF START CLIMBING TURN OFF ENGINE LET IT SIT FOR LITTLE WHILE TAKE A LARGE RAG OPEN RADIATOR PRESSURE CAP A LITTLE AT A TIME TO KEEP FROM GETTING SCALDING TO RELEASE AIR IN COOLANT SYSTEM.WHEN PRESSURE IS RELEASED OPEN PRESSURE CAP ADD MORE COOLANT IN THE EXPANSION TANK.CRANK ENGINE AGAIN LET IDLE WHEN TEMPERATURE GAUGE START CLIMBING. TURN OFF ENGINE WAIT FOR WHILE BEFORE OPEN RADIATOR PRESSURE CAP.WHEN YOUR THERMOSTAT OPENS WHEN TOP RADIATOR HOSE IS HOT AND ENGINE COOLANT TEMPERATURE GAUGE STOP CLIMBING AND COOLANT LEVEL STOP DROPPING IN THE EXPANSION TANK.ALL AIR IS EXPELLED FROM COOLANT SYSTEM TO KEEP ENGINE FROM OVERHEATING.

you dont have to bleed the water it automatically takes out the air when it runs and the thermostat valve opens check the level again after a run of 5 miles or when the temp is in the middle

remember not to check when the engine is hot

a common V6 failure is the intake manifold gasket. coolant will usually leak behind the water pump on the drivers side, however it can leak at other locations on the intake manifold gasket.

coolant leaks from other areas include the heater core, hoses, expansion plugs, trans cooler, and coolant overflow tank.

You will see a switch with a wiring connector plugged into the radiators side tank at the right side. That is the low coolant switch

There could be a couple of reasons for this,

1. The thermostat could be stuck closed creating more pressure than normal. Your temp guage would show a higher temperature or you have another blockage in the system.
2. The expansion tank is too full.
3. The cylinder head may be leaking. If you fill the system run the engine to normal temperature with the radiator cap off, look for quite large bubbles coming out of the filler cap. If the head is badly leaking, they can be like a volcano. The temp will rise quickly from cold and the engine will overheat in a short distance.
It does seem odd that it would only spill over after 20 mins. Suspect that the expansion is over full first if your temp is normal. Let it run until it stops and see where the level is when the engine is cold.

the hose will leave from the top of the radiator into the bottom of the exspansion tank

hi don,t worry that is how it is its the expansion tanks overflow pipe and just sits there