I believe the 2002 SL2 all came with 4-cyl engines.
Best practice to change coolant is to drain the current fluid, refill with fresh water, run the engine until it is warmed up and the upper radiator hose is hot. Let the engine cool, and drain the radiator again, and repeat until the drain water is clear. Change out the thermostat and the radiator cap, and any hoses that look or feel suspect, then refill with the proper coolant mixed for your regional winter climate. Burp or bleed tbe system, and then get a cold one and relax.