The plastic overflow tank located on the passenger side of the engine compartment is pressurized. Thus it functions as the top tank on a radiator. So where is the over flow part of this thing and how does it work. I had to replace mine due to a hole worn in it. It dawned on me that there was no overflow line that peed water on the ground if the engine got hot and started to boil. But there was a line that seemed to function as that BUT it actually had a connection on to the intake manifold. So it appeared that rather than peeing water on to the ground, it vents it into the intake manifold.
Or does it?
Does anyone have any idea how any of that is supposed to work?

 

When mine overheated it peed out at the pressure cap

I would think that it SHOUD'VE gone through that line and led to white smoke -- an ingenious way to notify you of overheating if you haven't checked the dash lately

 

Well during the time frame when I had the partially plugged catalytic converter I got the little sucker rather hot a couple of times. A combination of a 70 mph speed limit and 7% grades with 115 degree heat running to Cotton wood had a tendency to get the heat gauge up into the red and on one trip I had enough lights come on through the dashboard to discover indicators I did not know it had. I never really had much faith in the heat gauge reading so when it got that high (looking back due to the partially plugged catalytic converter) there were never any side affects that bit so I sort of got into the habit of ignoring them. But the day everything came on it was 120 degrees on a July 4th week end going to a party in Cottonwood and typically I was driiving too fast and I was in the middle of absolutely no where. I stopped the car and opened the hood and I could hear it boiling but could not see any water coming out. The engine was still running and not missing and if I could make another 10 miles before it quit I would be near a service facility, food and telephones so I shut off the A/C opened the windows and sun roof and continued on and about a half a mile later it cooled down, indicators went out and the gurgle sounds of boiling quit.
Until I replaced that tank and found what would be the over flow line coming from the pressure cap plumbed into the intake manifold which explained why I never saw water hitting the ground. But it also did not smoke either.
The service literature that I have for the car, a Haynes fix your Saturn book and a Mitchell CD collection neither of which describe the theory of operation of how it is supposed to work. It to me remains a mystery as to what the intent is.
That period of time though sure left me with the impression that the cooling system was well designed in that I actually ran it hotter than I thought I did due to the partially plugged Catalytic converter and nothing ever got damaged or caused a side problem.
Saturns are gone and although I thought about a vue when it came time to replace my Chryco/Mitsubishi van, the variable speed snowmobile transmission stopped that in it's tracks and a little later the rebadged butt ugly Over-priced Chevy van did not appeal to me so I bought my Chrysler which I have no regrets with. I'll not own another one. I just find it hard to make this one go away, even though now I have to repaint it again and have the front seats re-upholstered and the passenger side windo is giving me problems. The car remains a pleasing car to own and drive.
Damn, GM made such incredible lousy marketing decisions.