* Water Pump Failure: This is the most likely culprit. The water pump circulates coolant through the engine. If it fails, coolant won't move, causing the engine to overheat. Flat hoses often indicate a lack of pressure within the cooling system, which the water pump provides.
* Thermostat Stuck Closed: The thermostat regulates coolant flow. If it's stuck closed, coolant won't circulate until it reaches a dangerously high temperature. This would lead to overheating and potentially flat hoses due to the lack of pressure.
* Clogged Radiator: A radiator clogged with debris (like rust, sediment, or scale) restricts coolant flow, causing overheating. While this might not directly cause flat hoses, the lack of circulation contributes to the overall pressure issues.
* Head Gasket Failure: A blown head gasket allows combustion gases to enter the cooling system, pressurizing it and forcing coolant out. This often results in overheating and potentially bulging or even bursting hoses, but the hoses might not be perfectly flat; they could be bulging before they fail.
* Cooling System Leak (elsewhere): A leak in the system (radiator, hoses, etc.) *could* initially lead to flat hoses as coolant is lost, but this is less likely to be the primary reason given that the truck is overheating. A leak would likely cause a noticeable coolant loss, not just flat hoses.
* Low Coolant Level: While seemingly simple, low coolant would severely restrict circulation, leading to overheating. However, you'd expect to see signs of leaking coolant if this was the sole cause.
In short: The flat hoses strongly suggest a lack of pressure in the cooling system, pointing towards a water pump failure or a stuck thermostat as the most probable reasons for the overheating. A head gasket failure is a more serious possibility that must be investigated, too.
You should NOT attempt to drive the truck until the problem is identified and fixed. Continuing to drive it with overheating could cause catastrophic engine damage. Have a mechanic diagnose the issue promptly.
