Why is the cooling fluid overflowing after opening the radiator cap on 91 protoge

If you can't keep fluid in the overflow you either have an external leak, you should see fluid on the ground after stopping, if no fluid is apparent you have an internal engine leak and need a mechanic to determine the cause and repair.

When the engine is cool, take off the radiator cap and add fluid till full. Also add coolant to the overflow tank if needed
To check the thermostat, leave the radiator cap off, turn heater controls to high heat, and start the engine and run it till at operating temperature (this is to remove air from the system.) Coolant level should drop a bit when the thermostat opens, so you may need to add more. Replace rad. cap when engine is warmed up.
The only way the thermostat would cause no heat is if it were stuck open. So feel the upper radiator hose as the engine warms up. It will be cold or cool till engine starts to warm up-should take about 10-15 minutes, and then the thermostat should start opening, and the upper hose will start getting hot. If the engine takes a long time to warm up, like 30 minutes, the thermostat may be stuck open, needing replacement. If all seems good, check the actuator doors (temperature blend door) on the heater case. The doors have to open properly to let air from the blower motor to pass across the heater core, and then out the vents.
Good luck. If the coolant level was low, that was likely the problem.

If the radiator is not heating then the thermostat is not opening, replace it. It is under the top hose in the engine block.

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.

You still have a lot of air in the cooling system and you have to speed up the water pump to get any coolant to flow through the heater. Let the engine cool off, then open the radiator cap and top off the radiator. Pour the coolant in at a rate slow enough to let the air bubble up without splashing the coolant back out. Once you get the coolant level up to the top overflow hose, the remaining air will be pushed out by expansion through the overflow tank once the engine gets hot, and will be replaced by coolant from the tank on cool-down.

If you dont have an external coolant leak anywhere under your hood that has shown up on your driveway it could be the intake manifold or the headgasket leaking. Also check the thermostate to solve the heat issue.

Check this procedure to how to replace a water pump (DIY Complexity: Moderate / Time: 3.5 hours):

Parts:
1. Water Pump

Tools:
1. Screwdriver
2. Scraper
3. 3/8 in. Drive Ratchet
4. Cooling System Pressure Tester
5. Needle Nose Pliers
6. Socket Set
7. Radiator Hook Tool

Supplies:
1. Coolant
2. Silicone Sealant

Steps:
Step 1 With the engine off and cold, open the hood and locate the vehicle’s water pump.
o Tip: Safety Tip:Always wear safety glasses when working on your vehicle. Wear other personal protective equipment (PPE) when necessary, for example latex gloves or safety shoes.
o Tip: Before removing the radiator cap, squeeze the upper radiator hose to verify that the cooling system is not pressurized.

Step 2 Remove the radiator cap.

Step 3 Install cooling system pressure tester. Apply the pressure indicated on the radiator cap or in the owner’s manual.

Step 4 Inspect cooling system components for leaks.

Step 5 Place a drain pan under the radiator. Open drain valve or remove the lower radiator hose to drain cooling system.
o Tip: Depending on the vehicle, lifting the vehicle may be required to gain access to the lower radiator hose.

Step 6 Remove the drive belts or serpentine belt.

Step 7 Remove any hoses connected to water pump.

Step 8 Unbolt water pump from engine. Remove the water pump.

Step 9 Using a gasket scraper, clean the mating surface on the engine block.

Step 10 Install new water pump and new gasket. Tighten bolts to manufacturer’s specifications.
o Tip: You may want to use a light bead of silicone designed for water pumps.

Step 11 Re-install any hoses and belts that were removed.

Step 12 Re-install drain plug or lower radiator hose.
o Tip: Squeeze the radiator hose. If it feels soft you may want to replace the hose at this time. Always use new hose clamps.

Step 13 Refill radiator with a 50/50 mix of coolant and distilled water, then pressure test the cooling system and check for leaks.

Step 14 Fill overflow reservoir with same mixture.

Step 15 Leave the radiator cap off, start engine and let it idle. You should see the system“burping” bubbles of air. Refill the radiator to the top.
o Tip: Most air is expelled after a couple minutes of idling. Be cautious of potentially hot fluid overflowing.

Step 16 Install radiator cap.

Step 17 Road test vehicle, keep an eye on the engine temp gauge if vehicle runs hot, there still might be an air pocket in the cooling system. The cooling system should be topped off after vehicle has fully cooled down.

Good luck.

How to Replace a Water Pump
DIY Complexity: Moderate
DIY Time: 3.5 hours

Parts:
1. Water Pump

Tools:
1. Screwdriver
2. Scraper
3. 3/8 in. Drive Ratchet
4. Cooling System Pressure Tester
5. Needle Nose Pliers
6. Socket Set
7. Radiator Hook Tool

Supplies:
1. Coolant
2. Silicone Sealant

Steps:
Step 1 * With the engine off and cold, open the hood and locate the vehicle’s water pump.
o Tip: Safety Tip:Always wear safety glasses when working on your vehicle. Wear other personal protective equipment (PPE) when necessary, for example latex gloves or safety shoes.
o Tip: Before removing the radiator cap, squeeze the upper radiator hose to verify that the cooling system is not pressurized.

Step 2 * Remove the radiator cap.

Step 3 * Install cooling system pressure tester. Apply the pressure indicated on the radiator cap or in the owner’s manual.

Step 4 * Inspect cooling system components for leaks.

Step 5 * Place a drain pan under the radiator. Open drain valve or remove the lower radiator hose to drain cooling system.
o Tip: Depending on the vehicle, lifting the vehicle may be required to gain access to the lower radiator hose.

Step 6 * Remove the drive belts or serpentine belt.

Step 7 * Remove any hoses connected to water pump.

Step 8 * Unbolt water pump from engine. Remove the water pump.

Step 9 * Using a gasket scraper, clean the mating surface on the engine block.

Step 10 * Install new water pump and new gasket. Tighten bolts to manufacturer’s specifications.
o Tip: You may want to use a light bead of silicone designed for water pumps.

Step 11 * Re-install any hoses and belts that were removed.

Step 12 * Re-install drain plug or lower radiator hose.
o Tip: Squeeze the radiator hose. If it feels soft you may want to replace the hose at this time. Always use new hose clamps.

Step 13 * Refill radiator with a 50/50 mix of coolant and distilled water, then pressure test the cooling system and check for leaks.

Step 14 * Fill overflow reservoir with same mixture.

Step 15 * Leave the radiator cap off, start engine and let it idle. You should see the system“burping” bubbles of air. Refill the radiator to the top.
o Tip: Most air is expelled after a couple minutes of idling. Be cautious of potentially hot fluid overflowing.

Step 16 * Install radiator cap.

Step 17 * Road test vehicle, keep an eye on the engine temp gauge if vehicle runs hot, there still might be an air pocket in the cooling system. The cooling system should be topped off after vehicle has fully cooled down.

Good luck (remember rated this help).

There are 4 things you want to check in this order.
1. Make sure your fluid level is up to specifications.
2. Make sure the fluid is travelling through the radiator freely(water pump).
3. Make sure your thermostat is opening. This requires a great deal of caution, leave the radiator cap open (if it has one) and run the engine until the top radiator hose gets hot, If you have no radiator cap, watch for water rising or dropping in the overflow tank.Also watch for bubbles within the overflow or radiator.Also put all temp controls on high on the climate control center and feel for hot air once the engine reaches operating temperature(185-200 degrees). If you don't get heat within the regular time slot of 10-15 minutes you will need a new thermostat.
4. If you discover a large amount of bubbles within the radiator or the overflow tank than you've got a headgasket situation and should not drive the vehicle until necessary repairs are made. Thank you, Dana