Ford runs hot and all sensors seem to be off lower thermostat housing unit need to be replaced It seemed to have been leaking from the overflow and I kept putting water in it, then one day it ran hot and i started putting water there because te overflow was full. When you go somewhere and cut the engine off it won't start. You have to wait a few minutes, I was told I needed to replace the lower housing thermostat I'm concerned about other damage, the car was driven about 3 months

The first thing you do is clear all the codes with your scan tool.

P0300 is just a random misfire where the ECM can't decide which cylinder it is on.

Here is the thermostat gasket

https://www.autozone.com/gaskets/thermostat-gasket/ford/explorer/2005

Here is the thermostat housing complete. It looks like it is plastic so probably cracked when you were tightening the nuts.

https://shop.advanceautoparts.com/find/2005-ford-explorer-thermostat-housing.c9762

This code is worrying, but if the sensors are saying Lean Mixture, that means it is dumping more fuel to compensate which doesn't cause 'heat'. Try running a bottle of Extreme Clean Fuel System Cleaner through it. Clean the connector contacts on the o2 sensors. Make sure the coolant system is full and no airlocks.

P1299 Code - Cylinder Head Overtemperature Protection ...

Kelley Blue Book https://www.kbb.com > obd-ii > p1299
This error code indicates that there's an issue with the heat in your engine. It may be defined as "Cylinder Head Overtemperature Protection Active," as " ...

..

Before even trying a new thermostat, try blocking air flow past the radiator and engine area with some cardboard in front of the radiator. If your temp. gauge shows below half all the time, try a hotter rated thermostat, one that stays closed just a bit longer. Say your t-stat is rated at 190 degrees, get one that is rated at 193 degrees- do small raises to avoid overheating-and in the summer, you may want to go back to the lower rated t-stat.. A parts store or Ford dealer could help you pick an optional thermostat.
To replace, drain enough coolant from the radiator so the level in the engine is below the thermostat housing. Take off the upper radiator hose from the thermostat housing. remove retaining bolts or nuts from the housing, any other obstructions, and pull the housing off, replace thermostat, clean the gasket mating area on the housing and the engine block, use a new gasket and fit all back together. Careful not to overtighten the t-stat housing bolts: the torque specs would be small-about 15-20 foot pounds of torque-just snug them down good-you can always go back and re-tighten a little if you see a leak. So, all back together, refill coolant and overflow tank, run engine with radiator cap off till engine is hot, and thermostat opens-this will helpyou bleed air out of the system. When thermostat opens, coolant level should drop a little. Shut off the engine, top up radiator and overflow tank as necessary, and replace radiator cap. Check for leaks.

could be burning it may need cylinderhead gaskets

4.6L Engine - replacing thermostat



CAUTION Never remove the radiator cap under any conditions while the engine is running, or while hot. Failure to heed this caution could result in cooling system damage or severe personal injury.

1. Drain the engine cooling system until the coolant level is below the thermostat.
2. Detach the lower radiator hose, the return hose and the degas bottle hose from the thermostat housing.
3. Remove the two mounting bolts, then remove the thermostat housing.
4. Remove the O-ring and thermostat from the housing. Discard the O-ring.

Figure - exploded view of thermostat and Housing - 4.6L engine

To install:

NOTE To prevent installing the thermostat with an incorrect orientation, the housing contains a positioning slot. Install the thermostat so that the bridge part protrudes into the housing, not into the intake manifold.

1. Position the thermostat and a new O-ring on the housing, then install the housing.
2. Install the two mounting bolts, and alternately tighten them to:
   1. 4.6L SOHC engines 15-22 ft. lbs. (20-30 Nm).
   2. 4.6L DOHC engines 89 inch lbs. (10 Nm).
   
   
3. Connect the lower radiator hose, the return hose and the degas bottle hose to the housing.
4. Fill the cooling system, then start the engine and check for leaks.
5. If necessary, top off the cooling system overflow reservoir.

1. Drain the engine cooling system.
2. Remove the air cleaner outlet pipe.
3. Remove the 2 thermostat housing bolts and separate the lower and upper thermostat housings.
   1. Discard the thermostat O-ring seal and remove the thermostat.
   
   

To install:

NOTE Lubricate the O-ring seal with clean engine coolant.

1. Install a new thermostat with the smaller plate facing upward and the O-ring seal.
2. Position the lower and upper thermostat housings together and install the 2 bolts. Tighten to 89 inch lbs. (10 Nm).
3. Install the air cleaner outlet pipe.
4. Fill and bleed the cooling system.

Almost sounds like you put thermostat in backwards. Sorry, it happens to the best of us and yes it's possible.

two things if the fans are coming on for normal egnine operation, then the thermostat is not opening. if they aren't then you have a bad coolant temperture sensor. I don't know what engine you have, but if you follow the top radiator hose to the engine you will find the thermostat housing to replace the thermostat. And the sensor is usually located on the housing or real close to it.

While the car is running look into the overflow and see if you see bubbles going into it. If you do you have a head gasket leaking. Also while the car is running, feel the upper radiator hose temp. and feel the lower radiator hose temp and compare how hot they are. If the upper seems to be alot hotter than the lower hose, your thermostat is stuck shut.

Have you checked inside vehicle to ensure there is no heater core leak? If not leak found there and leak at thermostat housing is not severe once at normal operating temp, issue could be with a cylinder head crack to an exhaust valve which generally vents coolant to exhaust with very little or none showing in oil.

Follow the main hoses that run from the radiator to the engine. There will probably be a upper and lower. One may have blown off or ruptured. Lots of light will be necessary. Alternately, to try and get a better idea of where it is leaking have someone with old clothes and saftery glasses watch the engine bay when the car is running. Make sure all clamps are tight on the hoses as well.

make sure the electric fan is turning on. it it is not you can pull the wire from the plug that is next to the thermostat housing and it should turn on and run all the time, if it is not bad. Make sure your thermostat is not sticking closed.