4.0l Why did the heater quit and then it started running hot?

So the overflow tank would be pressurized with a radiator cap. This would no doubt be higher than top of radiator and engine .Keep filling it without engine running and heater on hot, then start up, when engine gets hot and thermostat opens, water should leave overflow and you need to top up as required.

It would appear your thermostat is stuck in the closed position , find where it is on your engine, drain coolant and remove thermostat housing and stat, replace housing(liquid gasket OK) and coolant. now run engine, turn heater controls to hot leaving filler cap off, top up any water to max and replace cap now warm up to temp until fan comes on. if all ok replace thermostat with a new one and new gasket, you could also flush the sytem out at the same time with a hose pipe by loosening one of coolent pipes and flush radiator.

disconnect the heat hoses going into fire wall , put hose into one with pressure and flush as it sounds like it could be bloked in the heater core,the other thing that could be the problem be the hot ,cold switch as it restricts the flow to makes the heater hoter or colder , it might need tlc or replacing as it is manaul not elec

try taking the thermostat out, see if it still gets hot, if its a vg30 engine, there could be trapped air in the system, there is a bleeder valve on one of the heater hoses, passenger side, right at the firewall

This may be a simple thing, don't get to nervous just yet. A similar problem came up the other day on fixya.com in reference to another car. Because of the way cars are designed now a days it just may be possible that you have an air bubble or pocket. Usually this happens in engines that sit a little lower than the heater unit. The way you describe your problem with an oil change first, then car running hot, may be purely coincidental. Try these checks first.
1- check for leaks around the engine, any hoses you may have removed when replacing the parts you replaced, thermostat goose neck, and if after filling your radiator has the level mysteriously gone down.
2- is it possible to see and check your water pump, if you can grab the pulley and yank on it hard. Does it have play, if so it could be bad and leaking through the weap hole.
3-you may have a bad head gasket (BLOWN). This could be putting oil into your antifreeze or antifreeze into your engine. If it's in your oil you would have seen this when you did the oil change CHOCALOT MILKSHAKE and more than five quarts. If it's going into your engine then it's coming out your exhaust. When you start the engine, if the exhaust smells SWEET your head gasket is bad.
4- you say coolant temperature light on and coolant level OK. If as I said in the beginning AIR BUBBLE . Remove your radiator cap , run engine to operating temperature, put on your heater, fill your radiator till it maintains proper level. I hope it's this simple for you. GOOD LUCK.

The brown looking chiffon could be oil in the water. However, if you are sure the system is ok then I would check the actuator door motor on the heater and make sure it is allowing the heat into the car. Seems as if you have done as much as you can.

There is a blockage or leak in your cooling system. That may come in a few different forms:
Incorrectly installed thermostat
Water pump not functioning - you may see water dripping from the pump or a stain from the hole under the water pump.
Severely coroded hoses/coolant passages - if the fluid is brown and the inside of the radiator rusty
External leak - you would see fluid on the ground Internal leak - you would see steam/white smoke from the tail pipe or water in the oil (may look like chocolate milk or not), if the oil level is extremely high this would be a good indication
heater core bypassed

OK no big deal you are not the first and you wont be the last.
First thing have you run the engine since putting it in the radiator if not good...iF YES then it will take a little longer. but dont worrie
Take the bottom hose off the radiator and turn the heater to hot let out all the water and some oil will come out but not much as it will stick to the sides of the engine and radiator etc .
Refit bottom hose and tighten up the clamp then remove the thermostat and refit the top hose Now fill with water to 3 " from the top Now add 2 egg cups of washing up soap suds to radiator refit cap and start and run till the temp gauge gets to 1/4 up and then turn off and let it cool down for 1/2 hr and drain again ,and do the same 2 more times .
them on the 3rd drain it should be clean water and refit hose and check all clamps and wash thermostat and refit (the same way it came out)
refill with either coolant or Antifreeze and with heater still on hot start and run and all will be OK..
Let me know how you get on RON

With cool engine... open radiator cap and look inside radiator. Do you see lots of sediment and calcium growth on radiater tubes? If yes, a coring may be needed. If only slightly bad, a radiator flush may be needed... then refill with 50 percent antifreeze.

Good thermostat, cleaned cooling system, non-leaking water pump, good water flow via water pump... nothing else left (unless you put the thermostate in backwards)..

Let us know

Good Day,

Sounds like the thermostat is working properly, the only other cause for the valve/lifter noise could be the oil pump is not pumping enough oil up to the top of the motor. I suggest doing an oil change(if you haven'y aleready), be sure to flush several quarts through, after sitting for 5 years I'm sure the old oil is pretty sludgy, this well help rule out this possibilty. As far as the water pump goes, It either works or doesn't typically when they are on there way out the will leak from the gaskets. A bad head gasket would cause white smoke form the exhaust as coolant get's into the oil and is burned off, so I don;t hink this is the problem.

Here's a start for you, hope this helps and good luck