Radiator coolant not filling up

Okay, here is the problem. Professional diagnoised with need to replace intake manifold. The engine overheated only once up to the red and I shut it off immediately. Once cooled and added coolant was able to drive home okay. Another mechanic suggested Stop Leak. Decided to flush the radiator and add new coolant. Flush went okay...added Stop Leak...then tried to add coolant. It took one bottle and then about half of another and then it would not take anymore. Any ideas??

First off what year, model & engine size are we talking about?
Cooling systems on Lumina are not very big, unless you syphon the block it wouldn't take much more than that if any.

Sorry, I have been busy reading past posts for any help I can find. I have a 99 lumina with a 3.1 L engine. The man at the auto parts store said it should take about 3 gals of coolant.

I doubt it could take 3...1.5-2 most likely.

Be sure to fill it with the bleeder screws open, or you'll have trapped air...

Run it for 20 minutes at least after adding stop-leak, or it'll all just sit in a wad and cause problems...have to run long enough for the thermostat to oen and water to circulate it..

I just checked...capacity 1.6 gallons

I don't think we ran it that long. How would you fix the possibility of the Stop Leak being in a ball in the radiator? How would I know if that would be the case?

I don't think we ran it that long. How would you fix the possibility of the Stop Leak being in a ball in the radiator? How would I know if that would be the case?

Usually it likes to hog up the heater core and you don't get much heat...

Make sure the heat is on, and let it run a while...better yet, drive it.

Well I took the car for a drive and at first it started to overheat then it dropped down close to normal. After awhile I noticed that it never registered where it normally did but a little higher. I kept driving around and decided to check the bleeder valves and opened them up until coolant was coming out. I drove around some more and the gauge still read higher than normal. It also would go almost mid-way and then drop down a bit then it would cycle this over and over while I drove. At this point, there doesn't seem to be any coolant leaks under the car as I put cardboard under the engine area when I got done driving. I did notice a few small spots of oil on the driveway.

Does anyone have any idea on what is going on.

Also, if the car was not run long enough after putting the Stop Leak in at that time and it does clog up the heater core, what does one do about that?

To get a good bleed, fill with engine off, bleeders open. When coolant flows from them, close them up and run engine to operating temp with heater control to full heat. The let it cool for about 10-15 mins and carefully open the radiator cap and bleeders, then fill a second time until it flows from both.

Close everything up and take a ride.

Usually takes one or more heat/cooldown cycles to bring all the air into position to bleed....your description sounds like there might be a bit still in there. Air will get trapped in the heater core too sometimes, and airlock it, making the heat not work right....

If stop leak clogs a core, all you can do is try backflushing it, if that doesn't work it needs to be rodded out or replaced.