10/2/2004: Water Pump

Since I have several spares, I decided to disassemble and inspect the water pump on my car to decide if I needed to do anything to it.

I looked at 3 water pumps and managed to basically destroy two of them in the process (one of which already had a frozen bearing, so i don’t really count that ;-)

Here are the results of my analysis..

These pumps appear to come in two main types. You can tell them apart by looking at the fan belt pullies. “Type 1” has basically flat edges, and “Type 2” has a lip that curves up at the edge. Here’s a comparison photo. Type 1 is on the left, 2 is on the right.

What i’ll call “type 1” has a heavy cast fan belt pulley and 3 slot-headed screws holding on the back plate. These are very hard to remove. It seems very likely that at least one of them will snap in the process, requiring you to drill it out (not very easy to do when you’re trying to drill out (hard) steel that’s surrounded by soft aluminum!

backing plate bolts and one screw
The “type 2” water pumps appear to be an later design (just a guess, for all I know i’ve got that backwards). The cast belt pulley has been replaced by a much flimsier stamped metal piece, and two of the 2 slot-headed screws have been replaced by normal bolts. These are MUCH easier to remove without snapping off.

In my case, I had one of these that had been soaked in grease early in its life, and so had very little rust- the bolts came out easily, allowing easy access to the back plate. After destroying another pump, though, I learned that attempting to remove either the impeller or the (type 2) fan belt pulley is a bad idea. It’s likely that they will bend or snap, and turn the pump into scrap.


With my skill level at least, the pump seals and bearings (the parts that would fail) are really not servicable on these pumps. The only way they could be gotten at would involve a lot of heating with a torch, which would probably destroy the old bearing and seal anyway. So unless you’re really desperate, it’s probably better to try to find another used (or new) water pump than to try to rebuild one yourself at this point.

What you can do pretty safely is to rebuild the fan clutch assembly and replace the rear gasket (behind the plate). However, if you do opt to take off the plate, bear in mind that the screws could snap, and you could have to drill them out- try to avoid that by using tons of penetrating oil and patience.

I did succeessfully remove the fan pulley on a type 1 water pump, but this wasn’t really all that helpful in the end- I wasn’t able to remove the lock screw that holds the main pump bearing in place, nor was I able to remove the impeller. So I recommend just leaving the fan pulley in place.

Rebuilding The Fan Clutch

Here’s the basic procedure for tearing down the fan clutch portion of the water pump, that is, everything forward of the belt pulley.

  1. Remove the three nuts that hold on the plastic fan blades and outer ring.
  2. Pull off the fan
  3. Remove the 3 bolts and 3 adjusting studs that hold on the center ring, remove it, and set aside.
  4. bend down lock tabs on the center bolt.
  5. Using a rubber strap wrench to hold the fan pulley steady
    • Use an air chisel to loosen the center nut. I found this to be very effective, but it will deform the nut slightly. If you have a better tool for this, by all means use it.
    • Once the nut is loose, use channel locks to take it the rest of the way off.
  6. Using a 3-jawed gear puller, pull off the fan pulley, on its bearing It may even pull off without the need for a puller.

That’s about as far as I have gotten at this point. Once I start to reassemble the water pump, I will write another entry about how to inspect the electromagnets, the brush, and to adjust the fan clutch after assembly.


Based on the three pumps i’ve inspected (especially one that was well-preserved by oil and grease), here are what I believe to be the proper finishes for the various steel parts of the pump:

outer ring silver cad
inner ring silver cad
ring studs ?
ring nuts silver cad
inner ring bolts black oxide?
inner ring adjusting studs ?
center nut black oxide?
center lock washer silver cadmium
pulley flat black