Why is lower radiator hose cold when motor is at operating temperature?

HI Anon.
Remove your radiator cap (WHEN ENGINE IS COLD), run the motor and let it warm up a minute or two, have someone rev the engine a little while looking into the radiator. If the water goes down and/or you see the water moving, your water pump is good. If not this means that your water pump is bad and is not moving enough water through the system. Try Removing your thermostat and run the engine without it. Keep checking the radiator hoses to see if they are the same temperature. If they are not the same temperature the water pump is bad. If they are the same temperature your thermostat is more than likely the culprit. Hope this helps.

Air Temperature Control Blend Door Failure No Heat or no AC (dependes on where door sticks)

In all modern cars there is a tiny DC electric motor driven gear drive that moves a plastic door that blends heated and cooled air from the AC and the heater core, this is called (interestedly enough) the air temperature control blend door actuator. The motor that moves this door fails because the door starts sticking from warping, most common complaint is no heat but it can be no AC as well. To replace these parts (blend door and blend door actuator) you must remove the entire dash from the car. Always have this problem confirmed by a dealer or qualified repair shop as it is a very expensive repair.

Other causes of no heat in the cabin are engine thermostats that are stuck open (engine runs cold) or air bubbles in the cooling system.

The thermostat is a critical part of your coolant system, the system that circulates water and antifreeze (coolant) through the engine to keep it from over-heating. It is called a valve because it can open and close, depending on how hot the coolant is acting upon it.
The reason to put a thermostat in the coolant system is to allow the engine to reach normal operating temperature quicker (and therefore operate at peak efficiency) than without a thermostat.
When the engine is cold, the coolant is at normal outside temperature, so the thermostat is closed. This means when you start the car, the coolant starts circulating through the engine, but can't flow into the radiator. With a closed thermostat, the coolant just keeps circulating around in the engine until the car warms up, the coolant gets hot, and the heat acts upon the thermostat, causing it to open at a certain temperature (about 185-195 degrees F.), With the thermostat now open, the coolant can now enter the upper radiatior hose and flow down the radiator to cool itself down, before going back into the engine through the lower radiator hose.
So the thermostat is always found on a car in the area where the upper radiator hose connects to the engine. Thermostat closed-water can't circulate through the radiator. Thermostat open- coolant is forced through the hose into the radiator.
I hope this helps you understand the thermostat valve and why all manufacturers include them.

You likely have air trapped in the system. Trapped air keeps the heat sensing elements of the thermostat and sensor from functioning properly.
Easiest remedy is to either 1) jack up the front of the vehicle, (support the car with jack stands), when the engine is cold and with the heater set to high heat, disconnect the upper radiator hose and pour 50/50 antifreeze mixture into the upper radiator hose until antifreeze begins to come out of the radiator. Reconnect the hose and top off the coolant reservoir to the proper level for your vehicle. Start the vehicle and let it come to operating temperature. The vehicle may or may not have an air bleed located near the radiator cap, if it does, carefully loosen the bleed until all air escapes and antifreeze if present. If there is no air bleed. Once the vehicle has reached operating temperature (the lower radiator hose is hot to the touch, meaning the thermostat is open) shut the vehicle off and let it cool. Then open the radiator cap, releasing any pressure, add more antifreeze, and restart the vehicle. This should remove any entrapped air. Or 2) The alternative is to have the vehicle parked on a steep hill with the radiator at the up hill side and do the above process to remove the trapped air. Always block the rear wheels for safety.

the only way you should have to replace a heater core is if it leaks or gets plugged up. When motor is hot feel the two hoses that go to the heater core. one should be fairly hot and the other should be the same but if one is just warm then follow hose and locate a flow valve and check for operation. OPening and closing with control hot /cold knob. Check coolant level in radiator while cold as well as fill reservoir to full when cold. Also remove radiator cap when cold and warm truck and check for flow of coolant. if lower radiator hose is hot hot hot and upper hose is cool then thermostat may not be opening properly, or thermostat is stuck open not building heat. You didnt mention if truck was overheating?? If its not i'd check for the flow valve operation, if it is i'd make sure coolant levels are full and waterpump is working.

Upper Radiator Hose and Thermostat

A large part of a radiator's function is made possible by the upper and lower radiator hoses. The upper radiator hose controls the flow of engine coolant from the radiator into the car engine. In a cold engine, engine coolant is stored inside the radiator. The engine coolant is held inside the radiator until the engine becomes hot enough to warrant engine coolant circulation. When an engine reaches operating temperature, the thermostat valve, which is located at the far end of the upper radiator hose, opens up and allows engine coolant to flow from the radiator into the engine.

First check if you have any leaks in the cooling system , then check if level is correct(radiator and expansion tank , check level when car is cold , never open radiator when it's hot).
Then verify operation of radiator fan , if it's electrical fan it should comes on when temp. goes over normal,
if it's a clutch fan- it should pick up a speed and be more loud. If fan is not on and engine is starting overheating , check upper and lower radiator hoses.
If upper hose hot and lower hose cold or warm then you might have stuck close or prtially closed thermostat , difference between lower and upper hoses when t/stat works ok is about 10-15 degrees,
not really noticeable for hand.So if you don't feel a lot of difference between hoses temp. , and fan is not on , check fan or fan clutch itself.
If lower hose cold , replace thermostat and purge system.
If everything above is working properly , and it's still overheating , you may have bad water pump or head gasket.

make sure you have radiator full of coolant
run the car to operating temperature
check the operation of the cooling fan
feel the upper radiator hose and the lower radiator hose. they both should be hot.
if one is cold then you may have a bad thermostat or restricted flow
if cooling fan does not come on when engine is hot then you have bad cooling fan switch, relay or motor.
good luck

Hi


The a/c and heating systems on cars today are pretty complex. 10 years ago replacing the thermostat usually did the trick, but today there are electric motors that operate the "blend doors" inside the dash…directing air flow from the heater core and A/C evaporator core to the cab of the vehicle. Always start by checking the actual coolant level inside the radiator itself to make sure it is full.

Then feel the upper and lower radiator hoses to see if they are hot (when the engine has been running awhile and has reached normal operating temperature), then feel the two heater hoses leading into the cab of the vehicle to see if they are both hot as well.

If you feel a drastic difference in one of the radiator hoses, I would try replacing the thermostat and see what happens. If all the heater and radiator hoses are pretty much the same temperature I would suspect there to be a control problem in the dash controls or in the blend door operation and a visit to you dealer or a qualified mechanic is my recommendation.


Thanks

Rylee