Upper Radiator Hose Flat

[backporch]

I know this was addressed in other threads, but I don't get the logic behind the suggestions.

I started my 2000 explorer with 4.0 OHV engine. I dont know what its history is because I picked it up not running. It starts and runs well. As soon as it reaches operating temp (and I assume the thermostat opens) the upper hose gets sucked flat.

Suggestions online talk about the radiator cap and overflow tank/line. I verifed the tank/line are not clogged. I didn't try to swap the radiator cap, but is this normal behavior? I thought the cap/overflow were primarily designed to take up the volume changes that the coolant undergoes when it is hot/cold.

Could there be another reason for this hose flattening? Can my radiator be restricted?

Thanks for the help.

 

[GroupExploder]

That would in my humble, be the radiator cap. An $8 or so item just to experiment with. But what do I know, I went to several colleges---now I am in a learning curve since retirement.

 

[backporch]

I am not surprised by your response, but I don't get the idea of what is happening. The cap has a valve to allow overpressure to go to the overflow and ( somehow?? ) vacuum to pull coolant back in. I would think that when the hot coolant first makes its trip through the radiator it would, if anything, need to push some hot coolant out.

 

[974X4BLACKSPORT]

Two reasons the upper hose can go "flat":
1) when the engine cools down and coolant begins to be drawn back into the engine from the over flow resivour and past the radiator cap, if the cap does not allow coolant to flow back into the radiator, the vacuum created can flatten a weak/old/soft hose.
2) when the engine is running and water if flowing past the thermostat and into the radiator throught the top hose, if the top hose is weak/soft it can collapse or "flatten" restricting water flow into the radiator.

 

[Mbrooks420]

Get a new hose, and a new cap. Cheap insurance against ruining a motor over a super easy to replace trivial part.

 

[koda2000]

I'd replace the radiator hoses and install a new rad cap. No reason not to try that first. I'm thinking soft upper hose, They rot front the inside and may look fine, but they aren't.

 

[backporch]

ok. fair enough. sounds like this is not normal. I agree replacing the hose is a good idea. My son had a 2000 mustang that had a spring inside the lower hose which must have been the suction side. The replacement may have been made thicker and the spring was no longer needed.

 

[Runnin'OnEmpty]

Since you don't know the vehicle's history, I'd insall a new thermostat. The old one may be sticking closed or possibly installed backwards. At operating temperature, the cooling system should be pressurized, but yours seems to be pulling a vacuum on the radiator...???

 

[backporch]

The upper hose which is connected to the thermostat should be ??delivering coolant to the radiator?? and the lower is the return? In that case a flattening upper hose makes even less sense when the thermostat opens.

 

[shucker1]

In that case a flattening upper hose makes even less sense when the thermostat opens.

If the thermostat is even opening. It could be so clogged up with sediment it may not flow properly when and if it does open.

 

[974X4BLACKSPORT]

The upper hose which is connected to the thermostat should be ??delivering coolant to the radiator?? and the lower is the return? In that case a flattening upper hose makes even less sense when the thermostat opens.

The upper hose (on standard flowing cooling systems like the Explorer) flow into the radiator (hot is top) cool water (lower hose) returns to water pump. And yes the hoses can flatten, when old and weak, seen it happen on my friends 67' Mustang w/302. Had a problem overheating when driving on the interstate, but cooled when came to a stop. Revving the engine when in "PARK" I saw the top hose flatten out and restrict the water going into the radiator (old weak hose). Sometimes you will see new hoses come with springs inside them to prevent this from happening (top and bottom hoses).

 

[CDW6212R]

The top hose is the pressure side, it shouldn't collapse unless there is a big restriction at the thermostat/outlet of the engine.

I'd at the least change the T'stat and look for problems there at the upper hose area. Replace the hose also, and if you don't know how old the cap is, that too. At the right age it's time to do all of the coolant hoses, cap, T'stat and coolant. If you bought it recently and don't know the history, I suggest doing it all.