There is no heat in the cab. The thermostat has been changed, the heater core is flowing free, the coolant is fine. The lower radiator hose continues to stay cold. The upper heater hoses stay between 130 - 135 degrees.
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Bad coolant flow. check for low coolant, also a thermostat could be restricting proper coolant flow. If coolant is full in the radiator than touch your upper radiator hose to see if it is hot. If their is proper coolant level and engine is warmed up to temp and radiator hose is cold replace your thermostat.
Look for an air block in the heater core, or a water valve in the heater hoses that may be closed. The normal way to purge air from the coolant system is to run the engine with heater on high heat, and with the radiator cap off, until the thermostat opens and the engine is at normal operating temperature. Then shut off engine, top up the radiator and overflow tank, and replace the radiator cap. If hot coolant is still not circulating through the heater core, you may have to get inventive and crack the outlet line loose to get flow started.
Both of the hoses at the heater core should be hot. If one is cold the heater core is plugged.
You can think of it this way. If the thermostat was stuck closed and you checked the upper and lower radiator hoses with the engine hot the upper hose would be hot and the lower hose would be cool because there is no flow. If you check the hoses with a properly working t-stat both hoses will be hot when the t-stat is open and coolant is flowing.
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Sounds like either you are low on coolant, the thermostat is faulty or your water pump has broken impellers causing poor circulation. Usually when a heater core goes bad, your passenger floor will be wet (because of leak in core) and you will have residue on the windows and a noticeable change in the amount of coolant in the reserve tank. If the thermostat is stuck closed you will have only what antifreeze is able to circulate between the engine,heater core and overflow tank as it will not be able to pull in antifreeze from the radiator. best bet is to look for leaks after verifying a full tank, then start with the thermostat( the most common) plus its the cheapest fix ($2-$6) for the part.
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.
Follow the upper radiator hose from the radiator to the motor. There should be two bolts holding the hose-to-block outlet in place. The thermostat is directly below this in the intake manifold. Before you take it all apart, check your radiator coolant level. If it's really low, there will be no flow of warm coolant to the heater core and you wont' be getting heat in the cab. Fill to the recommended level and recheck your heater...
Why was radiator replaced?Did it have heat before ? If it was plugged, the heater core may also be plugged. Try flushing it with a water hose in both directions. I dont know why the botton radiator hose would be cold, the radiator should be a uniform temp and the air coming through the radiator should be HOT, when the engine is at operating temp. What condition was the old coolant? if it was rusty, the water pump may have lower flow than normal.
No, you just won't have water flow through the heater core, Coolant flows through the engine through the lower radiator hose as the water pump sucks it out of the radiator and pushes it through the engine. It then flows out the top radiator hose when the thermostat opens. It then flows into the radiator to cool off.
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