Lets talk caps.
My old Radiator cap (stock from 1994) had some issues, the spring got really loose and was spewing out fluid. So i got a new one
It looks like this


But, the problem with that is, that one leaks too.
So i bought another one, from a different store.
That looks exactly like the one pictured.
Which leaks too.

I changed my Radiator about a year ago. I dunno if that has anything to do with it. But i think the opening size might be longer than what the normal cap is.
Any ideas? i was thinking about going to the Junkyard and snagging a one from a truck.

 

Measure your filler neck and the filler neck at the junkyard or parts store. Where is it leaking from, just under the cap? Maybe inspect very close for hairline cracks

 

Did you put an aftermarket rad in when you replaced it? If it was I'm surprised it didn't come with a new cap. I was thinking that maybe it was a little different than the stock one until you said you were using the original one. Are your new ones and the old one the same depth and size? What about the gasket/seal on it?

 

By any chance has the overflow line split?

 

Overflow line is new.
Aftermarket Rad when i replaced it. But yea, i thought it was odd that it didn't come with a new cap when i did it also.
It appears to be leaking from right under the cap. I haven't actually seen it, but i have cleaned it and then checked it after i drove it and it was covered again.

 

Have you tried an OEM Motorcraft cap?

 

Thats the idea. but i don't work at a Ford dealer, nor do i want to pay dealer prices.
So i figure if i go to the Junkyard and swipe one off of something with a 4 core rad like mine. I'm pretty sure there is a mint Expolder in the yard by me, a buddy of mine wanted the rear axle out of it, so i might make a trip one day this week and figure the crap out.