* Water pump failure: This is the most common cause. The water pump circulates coolant through the engine and radiator. If it's failing, it won't effectively move the coolant, leading to a cold bottom hose.
* Thermostat stuck closed: The thermostat regulates coolant flow. If it's stuck closed, coolant won't circulate through the radiator until it reaches a very high temperature (which explains why the engine isn't overheating yet, but is potentially close).
* Airlock in the cooling system: Air trapped in the system can prevent proper coolant flow. This is more common after a coolant change or repair.
* Clogged radiator or hoses: A severely clogged radiator or hose can restrict coolant flow.
* Failed radiator cap: A faulty radiator cap can prevent the system from building the proper pressure, hindering coolant circulation.
* Restriction in the cooling system: Something might be partially blocking coolant flow somewhere in the system, such as corrosion buildup inside the engine block or radiator.
Why the engine isn't overheating (yet): The engine might still be managing to dissipate *some* heat through convection and radiation, but it's not efficiently transferring the heat to the radiator for cooling. This is a dangerous situation as continued operation could lead to overheating and significant engine damage.
What you should do:
This is not a problem to ignore. Continuing to drive with this issue will likely cause engine damage. You should have a mechanic diagnose and repair the problem as soon as possible. Ignoring it risks a catastrophic engine failure.
