I have been slowly getting my FD back on the road after many years. I finally got my temperature to stabilize at 85C. I drove it around the neighborhood probably not even close to a mile of driving once i pulled in back into the driveway i noticed i have a slight drip from lower radiator hose which probably just need to move the clamp closer up on the neck of the radiator. But then about 3-4 hours later i go back out into the garage and notice that my upper radiator hose has collapsed shut, i unscrew the thermostat housing cap (radiator cap) and upper hose goes back to normal size again. very strange to me. why would this happen? and how to fix?

 

What was your coolant level after removing the radiator cap? That's an indication of vacuum usually if the system is full, it wouldnt have the same problem. I say throw a new radiator cap on there, and see what you get =).

Also check for clogged return hose at the reservoir. However, a problem like this usually is the radiator cap failed to allow air back into the system neutralizing the vacuum.

-AzEKnightz

 

The Radiator Cap in gasoline engine has 2 features:

1. It helps hold pressure until a set point when it allows pressurized air to come out. Usually set at 2 bars or so.

2. When engine cools down, it must allow air to re-enter the cooling system to return to "zero" pressure state.

Look at the tiny flap inside the radiator cap and you will see.

When feature #2 fails, you get collapsed hose.

 

Well i have two caps a high cap and a low cap, which comes factory on FD? I'm using the one that has the gasket not attached to the actual cap. If that makes any sense.