Heater wont get hot - 2002 Mitsubishi Galant

You might have a bad thermostat, you might just be low on coolant, and check the actual radiator, not the plastic overflow tank. If both of those are fine, you could have a restricted heater core, you can check that by touching both heater core hoses, if one hose is hot and the other isn't, then it's clogged.

Check to see if your heater hoses are hot when engine is at normal operating temp. (180 to 220 degrees F) If they don't get hot like the large radiater hoses do, then your heater hoses are clogged, probably at the point they connect to engine. Remove heater hoses from engine and I bet you will see dirt, grime, and corrosion where you took them off, restricting the flow of coolent through your heater core.

how old is the thermostat? are any hoses cracked or sucked together. heater core may need to be flushed or replaced? good luck!

Does the engines electric cooling fan turn on when it gets hot? Does it cool off if you turn the AC on?

check heater control valve for rear heater, sounds like it's stuck shut

FIRST THE ONLY REASON FOR A THERMOSTAT IS TO GET HEAT INSIDE THE CAR SO WHAT YOU NEED TO CHECK IS THE HEATER HOSES GOING INTO THE HEATER CORE AND SEE IF EITHER ONE IS HOT IF ONE IS HOT AND THE OTHER ONE COLD OR WARN THEN THE HEATER CORE IS PLUGED IF BOTH ARE HOT THEN YOU HAVE A PROBLEM WITH A VENT DOOR IN THE HEATER BOX

Is the radiator full??
You need to get the engine hot enough to open the thermostat and recycle the coolant and then make sure it full!

is the heater tap working to let water through the heater core it may not be opening have to check operation of that

Make sure coolant is topped off. Check operation of heater control door. . Check for heater hoses being hot. If hoses are not hot after running awhile either your thermostat is stuck open or the heater vore is plugged.If it's not overheating your radiator is prbably ok.

heat exchanger not working look under dash find where cable goes from heater controls the hot and cold switch move back and forth to find it its not opening all the way when you move it to hot push it farther by hand this will open the airway for your heater core