7 Causes of a Cold Lower Radiator Hose
Cooling system troubles? Take note of your lower radiator hose. When coolant can’t flow, that hose stays cold. Normally the hose warms up after a few miles, but if it’s still cold, coolant isn’t transferring engine heat outside and you can expect overheating.
Keep reading as we look at what can cause a lower radiator hose to stay cold and answer some common questions regarding this particular part.
What is the Purpose of a Lower Radiator Hose?
The radiator’s primary function is to transfer the heat generated by the engine to the outside air. To do this, the engine (when running) circulates its coolant through the radiator.
Hot coolant from the engine enters the radiator via the upper hose. The purpose of the lower hose is to convey the cooled antifreeze back to the engine.
Reasons for a Cold Lower Radiator Hose
In all cases where a cold lower hose is evident, the antifreeze will for some reason be either partially or completely restricted from circulating through the radiator. Each of the following cooling system problems could cause such a restriction of flow:
1) Inoperative Thermostat
The thermostat fails to open or will only partially open when the engine gets warm. Coolant cannot properly circulate if the thermostat will not fully open. Thermostat replacement will be required.
2) Failed Water Pump
Several failure modes for the water pump can result in reduced or zero antifreeze flow through the pump. Water pump replacement will be required.
3) Loose or Slipping Water Pump Belt
The water pump will not run at full speed. Thus its flow rate is reduced. Check and replace all worn belts. If the belts are not worn, adjust them for proper tension.
4) Clogged Radiator
The passages in a radiator are quite small and with time, can become plugged by sludge in the antifreeze. A cool lower radiator hose is a common symptom of a clogged or faulty radiator. The radiator may require replacement but in some cases, it can be drained, flushed and new coolant installed.
Note: Cooling system sludge buildup can be mitigated by periodic flushing of the complete cooling system and installing new coolant. See your owner’s manual for requirements in this regard.
5) Collapsed or Clogged Hose(s)
Either or both radiator hoses may be collapsing during engine operation or may be clogged. Diagnosing the source of this problem will be required. Hoses blocked with sludge will necessitate a complete cooling system drain, flush and new coolant. Old degraded hoses will need to be replaced.
6) Excess Air in the Cooling System
This condition can allow an air pocket to form at the water pump such that it will not circulate the coolant. Excess air may be present due to improper system bleeding after new coolant has been installed. Or there may have been a loss of coolant due to a leak.
7) Low Coolant Level
Low coolant can permit an air pocket to form at the water pump such that it will not circulate the coolant. Insufficient coolant will have been caused by a leak often due to a faulty radiator cap or crack in the overflow tank. The leak must be found and corrected and the coolant level restored.
