In a closed cooling system, as the radiator fluid cools after shutting off the engine, the fluid contracts creating a vacuum in the colling system. This vacuum sucks fluid from the overflow tank via the radiator cap so as to keep the radiator full even when the engine is off. If the radiator cap's internal check valve is plugged or stuck shut, or the overflow hose/tube is clogged or not functioning, the vaccum will collapse the upper radiator hose instead of sucking fluid from the overflow tank as it should. Try to clean radiator cap by pushing on spring while submerged in clean warm soapy water so as to clean it out and also clean out overflow tank and hose/tube to make sure all gunk is removed. Also, make sure radiator fluid is clean. Better yet, drain and fill with new fluid. Should be done often anyway to prevent head gasket failure and or water pump failure. If no improvement, replace radiator cap with oem one from dealer. Do not use aftermarket. May not have check valve or may have improper pressure rating, leading to leaks and/or overheating.
Low on coolant, check valve in radiator cap faulty, air pocket,
Top radiator hose can collapse while the engine is cooling after being up to operating temperature. Heat expands, cold contracts. If your car is not overheating this is nothing to worry about. Of course you could replace the hose if this troubles you.
radiator hose needs replacing. use and heat will cause hose to collapse when worn out
drain the radiator down below the top hose and unhook the hose from the radiator and the engine and pull the hose off.
Look on top of the radiator and follow the hose from the radiator to the thermostat housing. Look on the bottom of the radiator and follow the hose up to bottom of the block.
Upper is hose connected to top of radiator, lower is hose connected to bottom of radiator.
1. Open the radiator cap. 2. Disconnect the top radiator hose. 3. Run the engine for a couple of minutes with the hose off. 4. Insert tap water hose into the radiator where the top hose should be. 5. Run water into the radiator until clear water comes out of the radiator top hose. 6. Continue idling the engine, remove the tap water hose from the radiator, shut off engine as soon as the water stops coming out of the top water hose of the radiator. 7. Reconnect top water hose and fill radiator with antifreeze. Start engine and top off antifreeze.
Look on top of the radiator and follow the hose from the radiator to the thermostat housing. Look on the bottom of the radiator and follow the hose up to bottom of the block.
The radiator hose which I assume you mean although you write rad, is connected to the radiator. One on the top of the radiator and one on the bottom. the one on the top
The thermostat has not opened yet.
At the to of the radiator.
When the thermostat is open the coolant will flow through the top radiator hose in to the radiator and out to the water pump through the bottom radiator hose