F250, 7.5 L engine

I was towing on a highway at around 60mph when I suddenly saw lots of steam come from under the hood. I pulled over and upon investigation, found out that I lost the radiator cap.

I refilled it with water, plugged it with garbage bag and made it to the destination, where a day later I replaced the radiator cap.

But why would something like this happen? I don't know how old the cap was.

Also my last repair was the temperature sending unit which screws into the engine block behind the T-stat (which I also replaced).

 

Strange! Is the flange on the filler neck bent? If so, the cap can't seat properly.

Steve

 

I replaced it and all seems to work properly. Maybe I loosened it a bit during temp. sending unit replacement (to relieve pressure) and forgot about it