My check gauge came on as my temp gauge pegged out today. I pulled off the freeway into a gas station after 1/8-1/4 mile. Coolant was leaking rapidly out of my 98 Explorer Sport. A few minutes after it stopped dripping antifreeze, I added about a quart of antifreeze to the radiator. Then looking underneath from the front it seems to be leaking from around the bottom of the waterpump just above the crankshaft. Does this happen often on the 4.0 sohc engine? How difficult is it to replace a waterpump on this engine - assuming that's the problem. Any advice as to what happened? Explorer has 120,000 miles on it. How much does a new waterpump cost? Thanks! This is my first post although I've been visiting for a while.

 

You might want to check your coolant bypass hose, it runs from the T-stat housing to the waterpump. Its about 4inches long and is slightly curved. You can see it from the front right behind the idler pulley. Mine recently ruptured and had massive coolant loss in a matter of seconds.

Dale

 

Had the same thing on my v-8. The first shaft seal in the pump goes out and starts leaking, kind of like a warning before it goes out all together. Mine was replaced under extended warranty but generally speaking water pumps are relatively cheap.

 

I've started to pull it apart. The leak was from the weep hole in the water pump. When I pulled off the waterpump, the impeller and a little metal part fell out. The metal part is like a 1/2 inch silver(steel)dia disk,1/16 inch thick, fastened to a 1/4 inch dia bullet shaped body about 1/2 long gold colored(cadmium plating?). The impeller is worn in one spot and the housing is worn in a corresponding circle. I'm taking off the thermostat now to see if that's where the part came from.

 

Yup, the piece that ruined the waterpump came from the thermostat. Up and running again with new waterpump and thermostat.