98 rad cap question =-

1998 3.1 i just flushed the radiator. and replaced coolant with original dex=-cool. had alot of gunking brown stuff sticking to side of resivior. flushed it with a water hose in it overflowing for awhile. question =- i forgot how the rad cap was installed. i have the owners book,but it don,t make sense to me. book shows "with tube" on opposite side of where resivoir tube enters rad neck. the "align vent " shows next to the tube . is the book correct? also if i go to autozone,etc. can i buy a repalcement that,ll work properly on this lumina ?

I would replace the cap definitely, source of problem with dexcool use anyway, just pops on and turns clock wise to lock.

The brown gunk is from dex-cool being exposed to air. This indicates a bad radiator cap. The filler neck has two steps, just make sure the cap is secured down to the second stop (push down and turn til it stops, then repeat). Radiator caps from Auto-zone/Advance are fine as long as they are of the proper pressure. Stant is a good aftermarket brand if you can't find AC-Delco.

The brown gunk is from dex-cool being exposed to air. This indicates a bad radiator cap. The filler neck has two steps, just make sure the cap is secured down to the second stop (push down and turn til it stops, then repeat). Radiator caps from Auto-zone/Advance are fine as long as they are of the proper pressure. Stant is a good aftermarket brand if you can't find AC-Delco. the brown gunk was not in rad. it was in resevoir. the little flap type cap on the resevoir looks like it,s consrtucted to allow air to pass around it. it don,t make sense. but how can i judge the G.M. engineers ?

the brown gunk was not in rad. it was in resevoir. the little flap type cap on the resevoir looks like it,s consrtucted to allow air to pass around it. it don,t make sense. but how can i judge the G.M. engineers ?
That residue in the jar is normal, and should not affect the remainder of cooling system, look down in the rad when empty, that will tell you what's what. Air will not get from the res. into the rad. unless the cap is bad.

That residue in the jar is normal, and should not affect the remainder of cooling system, look down in the rad when empty, that will tell you what's what. Air will not get from the res. into the rad. unless the cap is bad. i got mad and pulled the resevoir off for cleaning.man,that stuff was difficult to clean out. note = the bottom of the resevoir is like horseshoe shaped where it,s secured. you ain,t got to pry the securing plastic button all the way off. you can just pry it a bit and the resevoir will pull up off it. also note = i don,t think this part of the system was built to be air tight. there,s a hole built into the resevoir near the rear,top side.

i got mad and pulled the resevoir off for cleaning.man,that stuff was difficult to clean out. note = the bottom of the resevoir is like horseshoe shaped where it,s secured. you ain,t got to pry the securing plastic button all the way off. you can just pry it a bit and the resevoir will pull up off it. also note = i don,t think this part of the system was built to be air tight. there,s a hole built into the resevoir near the rear,top side.
Right, that has nothing to do with air getting into the system, if the coolant is kept at the proper level and the cap seals that's it short of gasket leaks.