1990 GMC S15 Water pump

Contrary to the above statement I think you do make sense and it is exactly what has happened to my 89 s15 4.3. The bearing seal failing will cause a weep of coolant onto your floor. One test of your water pumps functionality is to pinch the top radiator hose after you start it up, there should be a rush of fluid when you release it. You've replaced the radiator and the thermostat, did you flush the core and water pump at that time? Make sure that there is not anything in the cooling lines that could damage you hard work thus far.

To replace the water pump, you remove the top shroud of the radiator fan/ radiator cover, then remove the serpentine belt. Now the fan nuts, remove the fan and bell cover. Then the 4 bolts that hold on the water pump. There are 2 on each side, 1 high and 1 low. There may be a need to move/remove accessories like the alt. Or a.C. But not on the 4.3 liter. When putting it back, some silicone sealant on the gasket will help them stay put. Also a bolt on the top of each side will help keep the gaskets aligned. When the bolts are started, add the bottom bolts on each side to ensure alignment of the gaskets. Only when you know for sure that all is okay with the gasket alignment and that the bolts are in the right place do you proceed to tighten them. Do so to specs and do it evenly.