Radiator hose question

Hi all. I have a 2015 Explorer with about 115k. A few years back I noticed the top radiator hose was flat. A new cap took care of that.

Fast forward to just the other day I was checking under the hood (while cold) and noticed the top hose was a little compressed. Not flat, but a bit more oval than round. Yesterday I let it run for a while and the hose rounded out, and this morning after it cooled I checked again and now it’s a bit more oval. I had the coolant changed at about 95k. Coolant level is fine. Is this something I should get checked or not a big deal.

Oh, I did loosen the cap to see if that’d help but the hose didn’t expand.

Hard to say if you need to replace it. Upper radiator hoses resist expansion, lower radiator hoses resist collapse. I would not worry about it.
My ‘06 Mustang went 10 years with original hoses, only changed them when the radiator required replacement.

If it’s oval with the cap off, then that’s its ‘natural’ shape.

Radiator hoses are of much better quality than they were many years ago. They often can easily last decades and since the vehicle is a 2015 I would not worry about it unless there is an obvious flaw. That does not sound like the case here.

Did you notice it was compressed after the engine hadn’t been run for some time, e.g. overnight? Or did this occur when the engine had been running and the coolant was still hot?

Since the coolant is going from the engine to the radiator in that hose, it isn’t a problem.

You have exceeded the modulus of elasticity of your upper radiator hose and that is why its natural shape now is oval and not round as it should be.

The hose can still function for many years yet as long as he shape doesn’t bother you. My concern would be what caused the cooling system to develop enough vacuum to collapse the hose in the first place.

My first thought would be the radiator cap, but you don’t seem to be having the issue anymore. It could be that there is some debris in the overflow reservoir that got sucked up to the bottom of the overflow hose and sealed it that one time. You may need to remove the overflow tank and clean it out.

You should be due for a coolant exchange. That would be a good time to go ahead and replace the upper hose. If you just had this done, then wait until the next one is due. Verify the coolant change interval in your owners manual, they are just as important as doing oil changes on time.