How to change a thermostat in a 1998 corolla

The A/C causes the engine to work harder (that's why fuel economy suffers when it is run).

If your car has an electric fan - make sure it runs when the engine is hot. If it does not - you may have trouble w/o the A/C running if is gets warmer outside. Look for fail fuses, disconnected plugs, etc.

You may also have flaky thermostat that is not opening fully when needed to exchange hot water in the engine block with cooler water in the radiator.

First, check the coolant level. You should find a semi-transparent reservoir / tank located under the hood that has a cap marked "Coolant". The side of the tank should have two indicator lines - one for HOT and one for COLD. If the engine has been run up to normal temperature (so that it can provide heat in the car), you should see the coolant level at or slightly above the HOT line. If the engine is cold - first thing in the morning or after sitting for several hours - the coolant should be at or slightly above the COLD line. View these levels while the engine is off and the car is parked on a flat, level surface. If there is not enough coolant - you will need to add the CORRECT type for your car.

Hot Engine
(1) With the engine hot, add enough coolant to the tank to bring the level to the HOT line. You may have to check the tank several times after driving if the coolant level in the radiator is down a great deal. NEVER open the radiator cap when the engine is warm or hot!

or:
Cold Engine
(2) With the engine cold, add enough coolant to the tank to bring the level to reach COLD line. Additionally - with the engine cold - you can add coolant directly to the radiator by removing the cap. Start the engine, set heat in car to HOT and add coolant mixture to radiator until level comes up to the bottom of the filler neck. Once the engine is HOT (getting heat in the car) check and top off radiator as needed and put cap back on radiator.

Check the levels in the TANK several times over the next few days when cold. If the tank ever empties -you'll need to have this looked at by a mechanic.

you need to replace thermostat and radiator cap.look under hood around engine compartment.look for a radiator cap near radiator,add 50/50 antifreeze and water to coolant system to bring up boiling point.pure water will cause engine run hotter because water evaporate away,remove radiator pour coolant in the radiator until coolant stop dropping in the radiator now some vechicle pour coolant in the coolant overflow jug,pour coolant until coolant level stop dropping and the coolant level stay at cold full mark.start engie let idle few minutes, watch coolant level in radiator if coolant start dropping add more coolant, when coolant level stop dropping put radiator cap back on let engine idle until both top radaitor hose and bottom coolant hose get warm turn off engine wait until it get cool then take a large rag slightly open radiator just a litle at a time to keep from getting scaled.once radiator remove add more coolant if low,put radiator cap back on start the engine let it idle watch the temp gauge if temperature gauge going hot zone stop engine wait until cool then add more coolant,keep doing this until engine stop overheating going into hot zone and coolant level stop dropping,make the coolant overflow jug coolant level stay at full cold mark, dont let jug run empty if so air will get in the coolant system causing engine to overheat.

CAR OVERHEATING FIRST CHECK FOR LOW COOLANT IN THE RADIATOR COOLANT OVERFLOW JUG.IF COOLANT LEVEL IN OVERFLOW JUG LOW REFILL ADD COOLANT BACK TO THE FULL COLD MARK.PUT RADAITOR CAP ON COOLANT OVERFLOW JUG START ENGINE LET IT IDLE UNTIL IT OPERATING TEMPERATURE.MAKE SURE TOP RADIATOR HOSE GETTING HOT WHILE ENGINE WARM UP.IF TOP RADIATOR HOSE DONT GET HOT WHILE ENGINE IDLING YOUR THERMOSTAT COULD BE STUCK CLOSE CAUSING CAR TO OVERHEAT.IF TOP HOSE IS GETTING HOT.CHECK FOR COOLANT LEAKS CHECK TOP RADIATOR HOSE AND BOTTOM RADIATOR HOSE FOR LEAKS.CHECK FOR LEAKS AT THE RADIATOR CORES AND PLASTIC SIDE CONTAINERS.IF ALL IS GOOD ENGINE OVERHEATING WHILE IN A LONG TRAFFIC LINE, COOLANT FANS NOT COMING ON.COULD HAVE FAULTY ENGINE COOLANT TEMPERATURE SENSOR OR BLOWN COOLING FAN FUSE OR RELAY.COULD HAVE PCM FAULT.MAKE COOLING FAN ELECTRICAL CONNECTORS AND WIRING NOT DAMAGE OR BROKEN.

Here is a basic description of cooling system, the top hose going to engine is the supply hose the bottom hose is the return hose. On your overflow coolant reservoir there is a lower cold level mark and a hot level mark above it also there is an overflow drain spout several inches above hot level mark to relieve pressure if system is overfilled. As to a bleeder system, bleeders purge air from a system to allowed it to become primed (pressure built up) generally on hydraulic systems like brakes or pneumatic systems like a diaphram pump for example. the only drain available is the petcock valve at the bottom of the radiator used to drain coolant. Now to your top hose being empty, you can remove top hose to engine have a garden hose running into radiator and if radiator cores are not stopped up water should flow freely from hose if not radiator is clogged. If you have water flow now you can pressure test system it should hold between 15-18lbs pressure constantly otherwise check all hoses/clamps etc (if leaks were present before replace faulty component/s) your vehicles water pump circulates coolant and is what pressurizes cooling system. A faulty thermostat will also restrict coolant from entering the engines coolant passageways if it doesn't open and your vehicle would overheat soon after, but you should still have coolant in upper hose when engine is running regardless. If you can add other info like your vehicle is running hot or coolant light coming on I can narrow it down for you.

TO CHANGE RADIATOR FIRST YOU TURN OFF RADIO FIRST TO KEEP FROM LOSING RADIO CODE.DISCONNECT NEGATIVE BATTERY CABLE.RAISE FRONT OF VECHICLE SUPPORT ON JACK STANDS.REMOVE THE LOWER SPLASH SHIELDS.NOW YOU NEED TO DRAIN THE COOLING SYSTEM.CATCH COOLANT IN A LARGE DRAIN PAN.REUSE COOLANT IF ITS FAIRLY NEW.IF COOLANT VERY OLD CHANGE IT.PUT OLD COOLANT IN SOME EMPTY CONTAINER TAKE TO A GARAGE OR WHOEVER DISPOSE IT.DONT POUR ON GROUND.HARMFUL TO THE ENVIRONMENT.MOVE THE AIR INTAKE DUCT PASSES OVER THE TOP RADIATOR HOSE.NOW WHEN ALL COOLANT DRAIN OUT.LOOSEN UPPER AND LOWER RADIATOR HOSE CLAMPS.THEN DETACH THE RADIATOR HOSES FROM THE FITTINGS.IF THEY ARE STUCK GRASP EACH HOSE NEAR THE END WITH A PAIR OF ADJUSTABLE PLIERS AND TWIST IT TO BREAK THE SEAL THEN PULL IT OFF REMOVE SMALL COOLANT SURGE LINES FROM TOP OF RADIATOR THAT GOES TO THE OVER FLOW RESERVOIR..DISCONNECT COOLING FAN ELECTRICAL CONNECTOR.THEN REMOVE THE COOLING FAN.REMOVE DISCONNECT AUTOMATIC TRANSMISSION COOLER LINES GET READY TO CATCH TRANSMISSION FLUID THEN PLUG LINES. NOW UNSCREW THE FOUR BOLTS TWO ON EACH SIDE OF THE RADIATOR THAT ATTACH RADIATOR TO THE AIR CONDITIONER CONDENSOR CAREFULLY TIP TOP OF THE RADIATOR SLIGHTLY TOWARDS THE ENGINE.REMOVE THE UPPER RADIATOR SEAL AND LIFT RADIATOR FROM THE ENGINE.NOW IS THE TIME TO REPLACE THE UPPER AND LOWER RADIATOR HOSES WITH NEW ONES SINCE ALL COOLANT REMOVE I WOULD REPLACE THERMOSTAT AND RADIATOR PRESSURE CAP.NOW WHEN YOU GET READY TO INSTALL NEW RADIATOR USE SHEETS OF CARD BOARD PROTECT RADIATOR FINS AND CORES FROM DAMAGE WHILE SITTING RADIATOR BACK IN PLACE.ONCE YOU GET UPPER AND LOWER HOSES IN PLACE ALSO PLACE SMALL SURGE HOSES FROM THE OVER FLOW RESERVOIR TO RADIATOR NEW THERMOSTAT AND TRANSMISSION COOLER LINES ALL HOOK UP. START POURING ANTIFREEZE IN THE RADIATOR OR OVERFLOW RESERVOIR IF RADIATOR DONT HAVE RADIATOR CAP ON IT.POUR A FULL GALLON ANTIFREEZE AND A HALF MORE IF LONG AS THE COOLANT STAYS ON THE COLD LEVEL MARK ON OVERFLOW RESERVOIR DONT OVER FILL.IF YOU POUR ANTIFREEZE IN RADIATOR KEEP POURING ANTIFREEZE UNTIL LEVEL STOP DROPPING AND LEVEL OFF AT RADIATOR TOP.START ENGINE CHECK FOR LEAKS. LET ENGINE RUN UNTIL IT WARM UP TOP RADIATOR HOSE GET HOT.WATCH COOLANT LEVEL IN RADIATOR OR COOLANT OVERFLOW RESERVOIR WHEN THERMOSTAT OPENS COOLANT LEVEL WILL DROP.ONCE YOU HAVE ENOUGH COOLANT IN THE SYSTEM COOLANT LEVEL WILL STOP DROPPING.THEN YOU READY TO GO.LET ENGINE SIT A LITTLE WHILE CHECK COOLANT LEVEL AGAIN.COOLANT LEVEL IN THE OVER FLOW RESERVOIR SHOULD BE AT HOT MARK FOR HOT ENGINE AND WHEN ENGINE COLD COOLANT LEVEL SHOULD BE AT THE COLD MARK.IF POUR ANTIFREEZE IN THE RADIATOR COOLANT LEVEL SHOULD BE AT TOP OF RADIATOR BELOW PRESSURE CAP.