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Water Pumps 101

Contributed By: Mike Saltsgaver

Most all of our fsj's came stock with cast iron pumps (the exception being those with 6 cylinders & serpentine drive had aluminum bodies). All early models used 5/8" shaft ball-ball bearings; later V8's used 3/4" shaft ball-roller bearings. Depending on year, they will have a molded carbon against sintered iron or ceramic mechanical seal.

The mechanical seal is the weakest link. The typical life span of this type of seal is 60 to 70 thousand miles (some live longer, others don't), depending on how well the cooling system is maintained. Rust, hi-silicates, dry running, over-heating are the leading causes of early failure. Most aftermarket pumps have seals with sintered iron/molded carbon seals. By comparison, today's cars use Silicon carbide/Hard carbon type seals.

When bearings become noisey (a rumbling noise) or fail (that god-awful sound of a fan running into the radiator), the 2 most likely causes are slight leakage from the seal or an out of balance fan. In the first case, the seal can leak just enough to allow coolant to wick into the bearing, which washes out the grease. In the 2nd case, a bent fan blade, or defective fan clutch, will put a heavey "orbiting" load on the bearing & will cause the shaft to break.

The key things to remember are:

  1. Use good coolant in proper proportion with water (no, don't use straight water or straight coolant.....antifreeze depends on water as a catalyst).
  2. Never hammer (or put a heavy load) on the end of the bearing. It will "brinnel" the race ways of the bearing & it will fail.
  3. Never try to re-use a bent fan blade....the risk is not worth the cost of a lunched radiator when the bearing shaft breaks. If the fan clutch is wobbly, or has no "drag" when turned by hand, replace it too.
  4. Never dry run a water pump (you know, starting an engine with no coolant....even for a few seconds). This will take hundreds (or thousands) of miles from the life of the pump.
  5. Use an anti-sieze compound on the bolts before re-installing them to prevent galvanic corrosion between the steel bolts & aluminum front cover.
  6. When replacing coolant for some other reason than pump replacement, add about a half a bottle of Barr's Stop Leak, especially if the pump has several miles on it. The majic ingrediant in the stop leak is ginger root. The fibres will "scrub" any silicate deposites which try to stick to the seal faces on the old pump (the "charge" of new coolant will have more silicate content than the old coolant you drained out). For comparison, all new Cadillacs, Buicks, Saturns, & Oldsmobiles come from the factory with a few pellets of stop leak in the radiator, straight from the factory (since '94-'95).

AMC and Chrysler both employed a good rebuilder house (there are dozens of pump rebuilders....some good, some not) to supply a lot of their past model pumps (I supply some new pumps to them, but not for the fsj's). These parts are built using good quality bearings and seals. After market pumps are built using slightly less quality parts (even mine). Who knows what some rebuilders use (some even re-use bearings rather than putting in new ones).

Although I like to see Airtex pumps sell, I'd recommend at least pricing a pump from your jeep dealer (not sure the cost difference) if you have the time when fixing your fsj.

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