'02 Durango coolant doesn't seem to flow back into radiator from overflow tank. I have to open cap on radiator hose regularly to add coolant directly. Had pressure test done and replaced thermostat.

add coolant let it run til the thermostat opens to see where the level is at if you need to add more or not

If the coolant was hot when you noticed water coming out the radiator, that is normal from the heat expansion of the coolant. That is why there are coolant overflow tanks-also called coolant expansion tanks.
When refilling coolant, always top up the radiator, and fill the overflow tank to at least the cold mark level (about half-way up on the tank). With cap off, run engine till the thermostat opens- upper radiator hose will become hot-then shut off engine, add coolant to radiator as needed, replace cap. This method of filling will help to expel any trapped air in the system. Oh, and remember to set your heater controls on high when filling coolant, so the heater core and lines also circulate and expel air.
Check the seal on the radiator cap that it is still good. The cap seal is important to seal the coolant system, as it is a closed system under about 15 psi of pressure. The reason to pressurize the system is that the pressure will raise the boiling point of the coolant by about 10 degrees- important when you consider how hot the coolant has to be when running. OK, enough tutorial-I don't think you have a problem with the water pump! G'd luck, reeve.

Coolant flows to the overflow tank (white plastic tank- not to be confused with the washer fluid resevoir) when it is hot, then gets sucked back into the radiator when needed. In theory, you should never need to open the radiator itself. Just make sure the overflow tank is full to the cold line if your engine is cold, and full to the hot line if it the engine is hot. If you recently drove your car, the level will gradually change in that overflow tank (as coolant is forced out of the radiator and eventually sucked back in. Unless it is completely empty, you shouldn't need to add much.

YOU NEED BLEED AIR OUT THE COOLING SYSTEM.WAIT TO ENGINE COOL DOWN.YOUR VECHICLE YOU HAVE TO POUR COOLANT IN THE COOLANT OVERFLOW JUG UNTIL COOLANT LEVEL STAY AT THE FULL COLD MARK.THEN START ENGINE LET IT IDLE A FEW MINUTES WATCH COOLANT IN THE OVERFLOW JUG WHEN IT DROPS ADD MORE COOLANT UNTIL COOLANT LEVEL STAY AT FULL COLD MARK.WHEN COOLANT LEVEL STOP DROPPING IN OVERFLOW JUG.SCREW RADIATOR CAP BACK ON OVERFLOW JUG WATCH ENGINE COOLANT TEMPERATURE GAUGE AS COOLANT TEMPERATURE START CLIMBING TURN OFF ENGINE LET IT SET A WHILE KEEP FROM GETTING SCALDED.TAKE LARGE RAG PLACE OVER COOLANT OVERFLOW JUG CAP SLOWLY OPEN RADIATOR CAP A LITTLE AT A TIME UNTIL PRESSURE RELEASE.REMOVE OVER FLOW JUG CAP.ADD MORE COOLANT UNTIL COOLANT LEVEL AT THE FUL COLD MARK ON THE OVERFLOW JUG.THEN SCREW CAP BACK ON THE OVERFLOW JUG.START ENGINE LET IT IDLE AGAIN WATCH ENGINE COOLANT TEMPERATURE GAUGE WHEN TEMPERATURE GAUGE START CLIMBING.TURN OFF ENGINE WAIT A WHILE.CHECK COOLANT LEVEL IN THE OVER FLOW JUG.DO THIS PROCEDURE UNTIL THE COOLANT LEVEL IN THE COOLANT OVERFLOW JUG STOP DROPPING AND STAY AT FULL COLD MARK,WHEN THE TOP RADIATOR HOSE GET HOT THERMOSTAT OPENING AIR IS OUT THE COOLANT SYSTEM. WHEN ENGINE COOLS DOWN.CHECK COOLANT OVERFLOW JUG COOLANT MUST BE IN THE COOLANT OVER FLOW JUG AT THE FULL COLD MARK WHEN ENGINE COLD. DONT .DONT OVERFILL COOLANT OVERFLOW JUG.KEEP COOLANT IN THE OVERFLOW JUG IF YOU LET COOLANT OVERFLOW JUG RUN DRY AIR WILL BE DRAW IN COOLANT SYSTEM CAUSE ENGINE TO OVERHEAT.

REPLACE THERMOSTAT IF TOP COOLANT COOLANT HOSE GOING TO RADIATOR IS HOT TO TOUCH THERMOSTAT OPEN. TO BLEED COOLANT SYSTEM FIRST YOU NEED TO ADD COOLANT TO THE COOLANT OVER FLOW JUG UNTIL COOLANT LEVEL STOP DROPPING AND STAY AT FULL COLD MARK.WAIT 3 MINUTES IF COOLANT DROPS ADD MORE COOLANT UNTIL COOLANT STAY AT FULL COLD MARK.WITH RADIATOR OVER CAP OFF CRANK ENGINE FOR MINUTE WATCH COOLANT LEVEL AT OVERFLOW JUG.IF COOLANT DROPS ADD MORE COOLANT IN THE OVERFLOW JUG.WHEN COOLANT LEVEL STOP DROPPING IN OVERFLOW JUG.SCREW BACK ON THE RADIATOR CAP TO OVERFLOW JUG.WHILE ENGINE IDLING WATCH TEMPERATURE GAUGE WHEN TEMPERATURE START CLIMBING TURN OFF ENGINE WAIT A WHILE KEEP FROM GETTING SCALDED.WHEN COOLANT COOL DOWN SOME. PLACE A LARGE RAG OVER THE COOLANT OVERFLOW JUG OPEN CAP LITTLE AT A TIME UNTIL PRESSURE RELEASED, THEN REMOVE CAP ADD MORE COOLANT IN THE OVERFLOW JUG TO THE FULL COLD MARK.THEN REPEAT THE PROCESS SCREW BACK ON THE COOLANT OVERFLOW RADIATOR PRESSURE CAP.THEN START ENGINE WATCH TEMPERATURE GAUGE WATCH COOLANT TEMPERATURE GAUGE WHEN COOLANT TEMPERATURE START RISING TURN OFF ENGINE AGAIN WAIT UNTIL ENGINE COOL DOWN ENOUGH TO KEEP FROM GETTING SCALDED TAKE PLACE LARGE RAG OVER RADIATOR CAP WHICH IS THE COOLANT OVERFLOW JUG CAP OPEN CAP LITTLE AT A TIME UNTIL PRESSURE RELEASED ADD COOLANT UNTIL AT FULL COLD MARK. WHEN YOUR COOLANT LEVEL STOP DROPPING.AND TOP RADIATOR HOSE VERY HOT THERMOSTAT OPEN AND AIR IS OUT THE COOLANT SYSTEM. MAKE SURE YOUR COOLANT OVERFLOW JUG HAS COOLANT IN IT,WHEN ENGINE COOL DOWN CHECK COOLANT OVERFLOW JUG KEEP COOLANT LEVEL AT FULL COLD MARK.BECAUSE IF OVERFLOW JUG IS EMPTY THATS A SIGN RADIATOR COOLANT LEVEL LOW.WHEN OVERFLOW JUG EMPTY IT WILL ALLOW AIR GET IN THE COOLANT SYSTEM AND CAUSE CAR TO OVERHEAT.WHEN REPLACING THERMOSTAT ALSO REPLACE THE RADIATOR CAP ON THE COOLANT OVERFLOW JUG.

DID YOU BLEED AIR OUT THE COOLANT SYSTEM.TO BLEED COOLANT SYSTEM, FILL THE COOLANT SYSTEM THROUGH THE RESERVOIR TANK OR THE RADIATOR UNTIL THE FULL COLD MARK IS REACHED.BESURE TO USE 50/50 HALF WATER AND ANTIFREEZE.YOU CAN BUY ANTIFREEZE THAT IS ALREADY PREMIX 50/50.AFTER ADDING ANTIFREEZE TO RESERVOIR OR RADIATOR FILL RADIATOR TO FULL MARK OR IF YOU DONT HAVE RADIATOR CAP ON RADIATOR POUR ANTIFREEZE IN THE OVERFLOW JUG UNTIL COOLANT LEVEL STAY THE FULL COLD MARK.WAIT AWHILE UNTIL COOLANT LEVEL STOP DROPPING.NOW INSTALL THE RADIATOR OR OVER FLOW JUG CAP.START THE ENGINE AND ALLOW IT TO RUN UNTIL NORMAL OPERATING TEMPERATURE IS REACHED AND THE UPPER RADIATOR HOSE BECOME HOT.STOP THE ENGINE AND OBSERVE THE COOLANT LEVEL IN THE OVERFLOW JUG. THE COOLANT LEVEL SHOULD BE AT THE FULL HOT LINE.ALLOW THE ENGINE TO COOL UNTIL THE AMBIENT TEMPERATURE IS REACHED THEN CHECK THE COOLANT LEVEL IT SHOULD BE AT OR ABOVE THE FULL COLD LINE.ADD MORE COOLANT IF NECESSARY. WARNING BECAREFUL WHEN OPEN THE RADIATOR CAP OR JUG OVER FLOW CAP.USE A LARGE RAG OVER THE RADIATOR CAP TO KEEP FROM GETTING SCALDED.OPEN RADIATOR CAP A LITTLE AT A TIME TO KEEP FROM GETTING SCALDED.WAIT UNTIL ENGINE COOL DOWN BEFORE OPENING RADIATOR CAP OR OVERFLOW JUG CAP.WEAR SAFETY GLASSES.

COOLANT-ADDING ADDITIONAL
Do not remove radiator cap to add coolant to system. When adding coolant to maintain correct level, do so at coolant reserve/overflow tank. Use a 50/50 mixture of ethylene glycol antifreeze containing Alugard 340-2 y and low mineral content water.
Remove radiator cap only for testing or when refilling system after service. Removing cap unnecessarily can cause loss of coolant and allow air to enter system, which produces corrosion.

COOLANT LEVEL CHECK
The cooling system is closed and designed to maintain coolant level to top of radiator.
WARNING: DO NOT OPEN RADIATOR DRAINCOCK WITH ENGINE RUNNING OR WHILE ENGINE IS HOT AND COOLING SYSTEM IS UNDER PRESSURE.
Remove radiator cap. The coolant level should be to top of radiator. If not, and if coolant level in coolant recovery bottle is at ADD mark, check for:

• An air leak in coolant reserve/overflow tank or its hose
• An air leak in radiator filler neck
• Leak in pressure cap seal to radiator filler neck

TRANSMISSION and OIL LEVEL CHECK TUBES


I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

If everything is working correctly; thermostat, heater core, water pump, head gaskets, etc. Then that leaves the radiator cap, the overflow hose or the overflow tank as being the problem.

As the engine heats up the coolant expands flowing into the overflow tank. As the engine cools the coolant is drawn back into the engine from the overflow tank. but this depends on the vacuum created by the cooling liquid. the radiator cap has a "valve" that lets pressure out and vacuum in. If it fails then you may not achieve a good vacuum. The hose that connects to the over flow tank must be non leaking as well; if it leaked then coolant would not be drawn back into the engine, only air would be sucked in. And lastly the coolant has to be drawn from the bottom of the overflow tank. again we dont want to be sucking air.

Some engines require a vent screw to be opened when bleeding the air out of the engine.

WELL YOU NEED TO DRAIN COOLANT LEVEL BELOW THERMOSTAT LEVEL.YOU HAVE TO DISCONNECT MAF SENSOR LOOSEN AIRDUCT 2 LARGE CLAMPS LOOSEN REMOVE 4 SCREWS TO AIR FILTER COVER LIFT UP REMOVE COVER. THEN REMOVE AIR FILTER AND HOUSING, FIRST DISCONNECT MAF SENSOR.YOU HAVE TO DISCONNECT THROTTLE CABLE AND SHIFT CABLE.YOU HAVE TO DISCONNECT REMOVE THROTTLE BODY COOLANT HOSES DISCONNECT IDLE SPEED CONTROL VALVE CONNECTOR AND DISCONNECT TPS SENSOR CONNECTOR. THEN REMOVE THROTTLE BODY ASSEMBLY. YOU NEED TO BUY NEW THROTTLE BODY COOLANT HOSES AND NEW THROTTLE BODY GASKET FOLLOW TOP COOLANT HOSE TO ENGINE BLOCK.NOW YOU SEE CAN AND REMOVE THE THERMOSTAT HOUSING REPLACE THE THERMOSTAT.BESURE TO HAVE EXTRA COOLANT ON HAND.BLEED COOLANT SYSTEM WHEN DONE.TO BLEED COOLANT SYSTEM REMOVE RADIATOR CAP ON OVERFLOW JUG.THEN OPEN BLEED SCREW ON THE WATER PUMP BYPASS HOSE PIPE JUST A LITTLE.POUR COOLANT IN THE OVERFLOW JUG UNTIL LEVEL STOP DROPPING.STOP AT COLD MARK ON JUG.CLOSE BLEEDER SCREW ON WATER PUMP BYPASS HOSE PIPE.CRANK VECHICLE CHECK FOR LEAKS. START UP ENGINE LET IDLE FEW MINUTES THEN CHECK COOLANT LEVEL ADD MORE UNTIL UNTIL LEVEL STOP DROPPING.PUT RADIATOR CAP BACK ON OVERFLOW RESERVOIR. LET ENGINE IDLE WATCH COOLANT TEMPERATURE GAUGE.WHEN GAUGE START CLIMBING. TURN OFF ENGINE WAIT FEW MINUTES TAKE A LARGE RAG OPEN RADIATOR JUST A LITTLE YOU HEAR HISS NOISE.WHEN PRESSURE STABILIZE DONT GET SCALDED BECAREFUL.OPEN CAP LITTLE MORE.IF COOLANT PRESSURE STILL BOILS OUT WAIT 20 MINUTES ADD MORE COOLANT TO RADIATOR OVER FLOW WHEN COOLANT LEVEL STOP DROPPING.PUT RADIATOR CAP BACK ON START VECHICLE UP LET IDLE UNTIL THERMOSTAT OPEN. THEN FEEL TOP RADIATOR HOSE FEELS HOT THERMOSTAT OPEN WATCH TEMPERATURE GAUGE.IF GAUGE TEMP START CLIMBING TURN OFF ENGINE WAIT A WHILE.CHECK AND ADD MORE COOLANT.WHEN THE ENGINE CAN IDLE TEMP GAUGE STOP CLIMBING YOU HAVE BLEED COOLANT SYSTEM.KEEP CHECK ON COOLANT LEVEL.

The hose is an over flow drain. If you've seen no signs of leaks then most likely your radiator cap is bad. The cap helps to pressurize the cooling system, if it is bad it allows to much coolant out to the over flow tank and the extra is dumped while your driving. When you turn off your engine the fluid is drawn back into the radiator and your coolant mysteriously disappears.