Do i change the thermostat or temperature sensor

I would check the fan motor itself.

I would highly recommend to change the thermostat. I have a Toyota Dolphin RV had similar symptoms. Thermostat was opening but not fully opening. Change thermostat runs at normal temperature now.

run fault codes and look for a faulty fan/ temperature sensor

have you checked to see if the oil is milky looking if it is then its a head gasket

OVERHEATING CAN BE CAUSE BY MANY THINGS LIKE FAULTY THERMOSTAT AND FAULTY RADIATOR PRESSURE CAP,TOO MUCH WATER IN COOLANT SYSTEM NEED 50 / 50 WATER AND ANTIFREEZE.LOOK FOR WATER PUMP WEEP HOLE LEAK, IF COOLANT LEAKING OUT WEEP HOLE WATER PUMP BAD NEED REPLACING.CHECK FOR LOW COOLANT LEVEL, YOUR RADIATOR OVERFLOW JUG SHOULD HAVE COOLANT AT THE FULL COLD MARK IF NOT KEEP ADDING COOLANT INTO COOLANT OVERFLOW JUG UNTIL COOLANT STOP DROPPING AND FULL COLD MARK, IF OVERFLOW COOLANT JUG WAS EMPTY RADIATOR IS LOW ON COOLANT.WHICH CAUSE AIR IN COOLANT SYSTEM KEEPING THE ENGINE COOLANT TEMPERATURE SENSOR FROM BEING SUBMERGE IN HOT COOLANT WHICH TURN ON THE COOLANT FANS.WHEN ENGINE COOLANT TEMPERATURE GET CERTAIN SET TEMPERATURE LIKE 190 DEGREES THE PCM AND COOLANT SENSOR WILL TURN ON COOLANT FANS, IF VECHICLE OVERHEATING COOLANT FANS NOT WORKING EITHER YOU HAVE FAULTY ENGINE COOLANT TEMPERATURE SENSOR CHECK COOLANT FANS FUSE AND RELAYS. YOU CAN CODE SCAN CAR TO SEE IF YOU HAVE FAULTY PCM, FAULTY ENGINE COOLANT TEMPERATURE SENSOR OR FAULTY COOLANT FAN RELAY.IF COOLANT FAN AND ENGINE COOLANT TEMPERATURE SENSOR OKAY,YOU HAVE CORRECT COOLANT LEVEL IN COOLANT SYSTEM, THERMOSTAT AND RADIATOR PRESSURE CAP BEEN REPLACED, YOU COULD HAVE BLOWN HEAD GASKET CHECK ENGINE OIL LOOKS LIKE MILK SHAKE HEAD GASKET BLOWED ALSO WHEN HEAD GASKET BLOWED YOU CAN DRIVE CAR SHORT DISTANCE START OVERHEATING AND YOU LOOSE ENGINE POWER SUSPECT BLOWED HEAD GASKET.

Do you think that it's overheating because the temperature light is on? If so, then it's possible that you have a bad temperature sensor and not an overheating engine.
Look for other signs of engine overheating :
1. Sluggish engine operation.
2. Detonation upon acceleration (pinging).
3. Rough, uneven engine idle.
4. Coolant boiling in overflow tank.
If your vehicle is experiencing these symptoms, then overheating is indicated. One of the most common cases of overheating is a bad thermostat. Another common problem is a faulty cooling fan or fan circuit. The cooling fan can be checked by running the engine at operating temperature and turning on the AC control. if the fan does not come on, then a problem with the fan circuit is indicated. The thermostat can be checked by placing a cooking thermometer on the motor near the upper radiator hose where it attaches to the motor. the temperature should not go above 225deg. If it does, then replace the thermostat. If the temperature stays at or below this rating, then replace the temperature sensor. I hope that this information helps you with your problem and thank you for using Fixya.com.

WARNING : Be very careful when working around cooling systems when the engine is at operating temperature. DO NOT open the radiator cap (if equipped) or even the overflow tank cap when the system is hot. Always wear safety glasses. Remember that electric cooling fans can operate at any time, even after the engine is off. Keep hands away from fan when working in the engine compartment.

test your fan motor.run b+ and ground to your motor and see if it runs.if it doesnt it is probably your coolant fan switch located on the cylinder head or the coolant fan relay.hope this helps.keep posted.

Since you say you changed the thermostat, and that wasn't it then possibly the cooling fan is not functioning properly. Or bad water pump,inaccurate temperature gauge, radiator core blocked or restricted. These are just the most common reasons. Good Luck and I hope this helps a little

u should check for a faulty thermostat first, they are only a few quid and easily replaced. if no change ur most likely faults are a blocked radiator or faulty water pump. u dont sayhow old ur van is but after the thermostat go to the radiator, when its hot check the bottom of the rad to make sure its hot, also brown water means u need to bback flush ur cooling system. even tho u have changed some sensors doesnt mean u got the fan switch sender, dash board sender and fan sender tend to be different sensors, so just double check.

Turn on the AC--it should start the radiator fans immediately. If nothing, check the fuse for the fans. The relay for the fans is a solid state device that is controlled directly by engine computer. The computer reads the coolant temperature sensor which tells the computer when to turn on the fans for usual cooling. Try to turn each fan manually (engine cool) and check for bad bearings, or fan blades--both fans should spin freely without any noise. If the fans come on with AC, then replace the temperature sensor which should be located near the attachment area of the upper radiator hose on the engine. It will have a single wire attached, and look like a small brass plug with threads. Watch the engine temperature for a while after the repair as the overheating may have damaged the thermostat element. Hope this helps!