Probably just over a gallon - buy the 50/50 premix and just fill it up
Sounds like your cooling fan relay is shot. Ron J.
This is gonna be fairly unspecific but it sounds as if you have some loose electrical wiring and it is probably grounding out or shorting out on your frame. Once you find the break or loose wiring clean it up and you should be ok.
In most cases the single wire sensor runs a temp gauge or temp light. The double wire sensor feeds info to the vehicle's computer and operates relays for the cooling fans. This may or may not be the case for your Saturn.
If the electric cooling fan(s) are not coming on that may be the problem.
Saturn's equatorial radius is about 37,457 miles.
Use the Gold antifreeze. It lasts longer and does not cause corrosion to the cooling system.
Any type of antifreeze will work in a 99 Saturn SL1. Many people recommend using Prestone Antifreeze for cars that are older than ten years.
Dexcool
No vehicle actually burns antifreeze. If the antifreeze level in your Saturn seems to be going down, it's because of a leak.Possible antifreeze leak locations are:Coolant hoses.Radiator cap.Water pump.Heater core.Head gasket.Cracked head or block.Find out where the leak is occurring and repair it.
Dex-cool
The 1997 Saturn used dexcool antifreeze. The chemical compounds are different and should never be mixed, as the engine will no longer cool properly.
I had a similar problem and ended up replacing both the lines and the radiator.
To change the antifreeze on a 2003 Saturn Ion-3, locate the drain plug on the bottom of the radiator. Drain the liquid into a pan before refilling it.
Anti-freeze that is compatible with aluminium engines.
Match the color of your antifreeze to the new one you buy unless it states its good for all types.
1999 SL2 should have what is known as DEXCOOL in the cooling system. It's a GM special coolant that you can obtain at any Autozone or your preferred parts provider. The color in this should be a pinkish color if not orangish. Hope this helps you. DO NOT USE GREEN ANTIFREEZE/COOLANT IN YOUR ENGINE OR MIX COLORS OF COOLANT! YOU WILL CAUSE A GELATIN LIKE SUBSTANCE TO FORM, AND POSSIBLY CLOG/RUIN YOUR COOLING SYSTEM.
Autozone/ advanced auto usually has antifreeze that goes with either kind. I suggest that.