Replacing temperature sensors

Also get your friend to flush the system if it hasn't been done in awhile . I regularly get older rigs in that have issues with their breaks and cooling systems. Both need to be flushed every ten years min. Or you'll end up with failing systems.

The most common overlook thing is you got a air pocket, so before you go spend your money turn Heather on full blast, open the radiator cap, car running look for air bubbles, takes patience cause you got to wait for the thermostat to open up, you must refill the coolant really really slow snail pace, some car have a bleeding valve others have two chamber on the overflow bottle,good luck, if that doesn't work change the thermostat first and if that doesn't work I'm afraid you may need to replace water pump. . water pump

Have a cooling system flush..your heater core may be clogged.

Hello! The heater core is partially blocked...I would suggest flushing the cooling system with the temperature control on high...NOTE...The type of anti-freeze used in your vehicle is DexCool...If another type is used it may damage the cooling system...To flush...Drain radiator...Fill with plain water...Run engine until thermostat opens...Turn engine off...Let cool then drain...Do this at least three times or until water drains clear...Install new thermostat...Refill with 50/50 DexCool...Leave the radiator cap off as engine warms...Allow all air bubbles to escape...Then install cap...

The down side of DexCool is electrolysis...Electrical current flowing in the cooling system which can cause the anti-freeze to "clump" blocking its flow...Periodic flushing eliminates the problem...

Guru.........Saailer

I’m happy to help further over the phone at https://www.6ya.com/expert/david_6df67de3b14de867

Normally the engine operates at 195F, if you did not replaced thermostat with another one at 185F. If the temperature has a tendency to rise up, the reason is a partially obstructed cooling system or/and a bad thermostat.
The first part of the cooling system that gives up is the heater core, because the coolant flowing channels are thin. You got a good advice but not the best one. It is the time for a coolant flush in your car. To do do it right then you need time. Plan ahead for a week end. With a cooled engine, start as your friend advised you with the heater core hoses. Disconnect both of them, but the dirt has to go out of your car, so with a garden hose back flush it and let the dirt to get out of your cooling system. After you will get clean discharge, it is the time for coolant bottle, remove it, discharge the used coolant and clean it. The third to come is the radiator. Open the drain cook, or disconnect the lower radiator hose, and disposal used coolant properly. Now open the radiator cap and flush with water the radiator till discharge will be clear. You think that you are done? Not yet. There is half of old dirty coolant trapped in the system.
Install everything, and connect all coolant system hoses, radiator, heater core and coolant bottle. Now you have to run your car with water. Fill out the cooling system with distilled water, start engine, turn on the heater high, and run till upper radiator hose get hot. That means the thermostat opens.
Let the engine to cool down, open the radiator cap, and draining cook or lover radiator hose and drain everything. You can use flush detergent if you wanted at this stage, but flushing with detergent will add 4 more hours, because detergent is colorless and you have to guess how many fill and drain processes do do to get rid of it. I do not do it, but if your cooling system is very dirty you have to do it. After the last drain, fill the cooling system with concentrated antifreeze and 30% distilled water. The reason is because it is more water trapped inside the cooling system. The goal is to reach 50/50 concentration. You need a coolant tester to find this. Start the engine and add coolant til radiator is full. Install the radiator cap and bleed the system. After driving you car for a day or so, let engine to cool down, open the radiator cap check the concentration of coolant with the tester and add antifreeze or distilled water as necessary. It is a good idea to replace the thermostat while flushing the radiator. This procedure has to be done every 2 to 3 years. It is up to you to decide to use RED GM Dex-Cool or GREEN Prestone antifreeze.
In all my cars I have replaced Dex-Cool with Prestone, but I flush the system every 2 years, and I never had a cooling system problem in all my cars.

Temperature sensor is in intake manifold.
Water is not flowing smoothly through the manifold.
2 immediate things to try........
1. Replace the thermostate (about 6 dollars). If you drive the car to an Autozone for the thermostate purchase, they will show you where it is located and how to replace it.

2. Flush (thoroughly) the cooling system. No shortcuts here, buy the flush and follow directions. Have the heater turned on HI.

After the flush, fill with 50-50 antifreeze-water.

Problem within engine are done. Other issue MAY be the sending unit (as your Autozone guy about that... it looks like a spark plug and takes about 3 minutes to replace.

This code is for your Coolant Thermostat - It's detected that the Coolant Temperature is below the Thermostat Regulating Temperature

This code may mean one or more of the following has occurred:

• Low engine coolant level
• Leaking or stuck open thermostat
• Cooling fan running too much
• Faulty coolant temperature sensor (ECT)
• Faulty intake air temperature sensor (IAT)

Check the following to see if it resolves your problem:

• verify coolant strength and level
• verify cooling fan operation and replace if necessary
  
• verify ECT sensor operation and replace if necessary
• verify IAT sensor operation and replace if necessary
• if all above checks out, replace the thermostat
  

Some radiators do not flush well...sometimes the flush will go around obstructions instead of through them and sometimes flushing will loosen debris which can plug cores that were open. It is possible that your radiator is marginal and not transferring heat properly. Temperature generally increases after shut-down for a short time and that will turn on
the fan.That part is normal...the item of concern is running hot at idle, in traffic.
Likely if you don't have any leaks and the head gasket is good, changing the radiator should help.

Not certain, but you may be referring to the blue light that indicates when the water temperature in the cooling system is "cold". It's typically blue when the car first starts, then changes color when the water temperature rises. If the light remains blue the water temperature isn't heating up, and you may want to have the cooling system flushed and checked. Depending upon the cars mileage, it may be time to flush the cooling system anyway.