if you see the fld. move with the rad cap off when it gets hot it should also start exspanding and over flow thats what the res. tank is for. it might be you have a air pocket in the line somewhere, when it's cold is the rad. full and the res tank at it's full line ?

2001 5sp. K&N stock filter 215/70/15
If your check engine light is on at least you know the light still works