What cause lower hose to collapse after cool down

Hoses collapsed when water could not be drawn back into cooling system from over flow tank. There has to be an obstruction preventing water to flow back into radiator when car cools down.

Hi Larry:
Good observation. Not too many people would spot that.
When the engine is hot, the coolant is hot and expands. At the filler cap for the radiator, there will be a hose that goes to the overflow tank. As the coolant fluid expands, it flows through thie tube into the overflow tank.
When the engine is turned off, as it cools, the volume of coolant in the engine and radiator contracts, and is supposed to suck fluid back from the overflow tank.
I'm suspicious that something is preventing this from happening so the vacuum in the engine coolant system is collapsing the hose.
WHAT TO DO?
- Check the radiator cap. Make sure it is functioning correctly. Make sure that it is correctly installed and screwed all the way on.
- Check the coolant overflow hose. Make sure it is not plugged.
Odds are that you will find the problem quite quickly.
Cheerfuls.

I would start by replacing the radiator cap. A bad cap can stop the flow of coolant from the coolant reservoir back into the engine when the engine cools down. This will cause a vacuum and collapse the hoses.

The other possibility is the lower hose is starting to get weak. This compounded with a radiator cap that is not functioning correctly will cause the the hose to collapse when the engine cools off.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

When an engine is shut down, the coolant temperature begins to drop. If the vacuum valve in the radiator cap fails, the resulting vacuum in the cooling system can cause a radiator hose to collapse

if cooling hoses do that sounds like you have the wrong type of hose for that applaction, its common for cooling systems to contract or produce vacume when cooling but should not collapse

Check the lower hose that it does not collapse when hot.The wire spring inside the hose may have been crushed and water not flowing.Be sure there's always coolant to the level in the catchcan/reservoir and keepit at the mark/level,being it's been on the road this long,may need to backflush radiator by unhooking the lower hose from engine and hook a garden hose to the lower radiator hose and turn the hose on with engine running.When the thermostat closes from the cool water,it will slow down running from engine where lower hose connects meaning the thermostat is good.Otherwise,replace the thermostat.Takes a bit of work,but you know what's up with this procedure.Rigger.

replace radiator cap

A collapsed hose will restrict (or completely block) water flow, causing a overheating condition. Before you do anything else, replace the hose. Some aftermarket hoses are available with a wound steel coil that will prevent a hose from collapsing.

Good time to replace all the hoses and thermostat. If I were you, I'd also flush the cooling system while I was at it. Probably wouldn't be a bad idea to take a look at your serpentine (or "v") belt to.

If your particular vehicle has air bleed ports, be sure to properly bleed all air from the system when refilling with coolant. Usually the bleed ports will at or near the point of attachment of both the upper and lower radiator hoses to the engine block.

Good luck!

hose faulty wall of hose weak
or there is a vacum being created on your cooling system when it coling down

Antifreeze should be mixed to a 50/50 solution. Never straight antifreeze.

It is possible that before your system was worked on it did not have the circulation to collapse the hose. Usually hoses would have a metal spring in them to maintain the shape of the hose or the hose would be molded with Ribs to strengthen the shape of the hose.
See if Autozone, Oreillys, or NAPA list a hose for your car and ask for one with Ribs on it. Get a cheap antifreeze gauge or let Autozone test the water for the mixture.