Lehman 120 cooling hose collapse

I have twin 120 Lehmans. On the port engine, the large diameter cooling hose coming up to the expansion tank on the port side of the engine collapses when the engine cools down after a normal 185 degree engine run. After the engine has cooled, I open the expansion tank cap and the hose comes back to normal. When cool, the coolant level is just below the bottom of the cap and the same as the starboard engine which does not have the collapsing hose issue; and I lose no coolant during running.

Any ideas what is going on? I do not have the tank coolant recovery upgrade done on either engine.

If it is cap related, I could swap starboard and port engine caps and see if the problem moves to the starboard engine hose...

Greetings,
Mr. 83. The first things that come to mind are weak hose or bad cap. Check your overflow tube (copper) for blockages.

Radiator cap

Squeeze the same hose on the other engine and see how it feels (please no jokes). We had the same issue on our FL but a different hose. The collapsed hose was coming off the back of the heat exchanger. The replacement hose had wire. But while you’re at it, change the cap if you don’t have any history. Let us know what you find.

Thanks all... I will start with the easy fix first... I have a spare cap from American Diesel. I will take the cap off Starboard engine and put it on the problematic port engine and put the spare on the Starboard engine... I will also squeeze starboard and port hoses to see if they feel the same....

Plese keep us informed as to how your hose feels when you squeeze it...

And just so you know ADC sells a replacement hose kit for pretty cheap. if you dont know the age of the hoses its good PM.