this is a 91 f150 4x4 5.0. back in the begining of december i had somewhat foamy liquid leaking from the airfilter box, coming in from the crankcase filter hose. i figured it was the intake gasket. no leakage from the weep hole on the water pump. so i added 2 bottles of the prestone super stop leak stuff. it slowed the leak alot but not 100%. i only drove the truck about 500 miles like that. last week i noticed that when i started the truck , when it warmed up the temp gauge would go 99% of the way to the red line on the temp gauge, with no heat while it did this. then would fall to the normal range with full heat. then while driving at any speeds, it fluxuates between the halfway point and 3/4 range depending on rpms, with full heat always. well now the antifreeze backs up into the resivoir and over flows the res, but leaving the radiator really low. the water pump is sqeaking in the meantime since the airbox deal.

now i know i should have fixed this a long time ago, but now i need to know what to fix. it sounds to me like a water pump now, but................is the t-stat sticking? or worse? any thoughts a helpful. also no check engine and no codes to be read

 

Sounds like a bad head gasket, I'd get the system pressure checked.

 

You might also have a leak in the hose between the radiator and the recovery reservoir, letting the radiator suck air instead of coolant as it cools.

Steve