if i am not mistaken you have the closed system. i had the same problems on my 90 . i ended up pulling the thermastat & drilling 2 small holes in it. like 1/4 or smaller holes. that allowed the air to burb out fully. those dang closed systems are next to impossible to get all of the air out & that will give you grief. also, keep an eye on your pressure bottle make sure it doesn't start to look like a banana. they have have a really bad habit of warping & that will cause your system to fail. make sure that when you are burping the air out of the system that you have the heater on the whole time.