I am looking into buying a 1995 F150 with a 300 I6 and a 5 speed. I test drove it today and it did fine. No missing, sputtering, or overheating. When I got back I noticed that the top Radiator hose was flat. The guy said it needed a thermostat but I'm not sure. I checked the oil and there wasn't any water in it. I'm just curious what could be causing this because I really like the truck and it's a good deal but I do not want to get myself in a mechanical nightmare. Thanks, Austin.

 

A bad radiator cap can cause that .

 

That's what I've heard. I just want to make sure it's not a major mechanical problem. I mean even if it's the water pump or something like that I can do that myself. I just hope it's not the head gasket or something like that. I can't do that. Thanks for the response.

 

This happened to me when I idled my engine without the belt on the water pump. I was listening for noises and pulled the belts off. I didn't figure the temps would hurt it by only running 20 seconds or so.
However, unexpectedly, all of the radiator hoses sucked flat and I had to quickly turn the engine off. When I hooked the belt back up and spun the water pump, it went back to normal.

My guess is it's a bad water pump and/or thermostat. The lack of circulation is causing a vacuum in the system. A new water pump, thermostat, and radiator cap and it should be good. If you're overly concerned, replace the radiator and hoses while you're at it.

Either way, I can't think of anything engine-wise that would mechanically cause this. Just circulation (or lack thereof) in the cooling system.