How To

DIY Garage: How to replace a water pump

Water pumps fail in a variety of ways: they leak, they get noisy, they don’t pump, or they can simply self-destruct.

Water pumps fail in a variety of ways: they leak, they get noisy, they don’t pump, or they can simply self-destruct. Fortunately, many cars use a conventional pump that’s within grasp of a DIYer.
Spot the problem

Obvious leaks are not difficult to spot. But a persistent, minor coolant loss with no obvious leak may be a water pump. They’ll often only leak when the vehicle is warmed up and running.

I’ve had to add small amounts of antifreeze to the overflow tank of my ’87 200SX for a little while, but I have not seen a leak. With the help of a mirror, a quick check of my water pump’s weep hole (used to allow any coolant that makes it past the shaft seal to escape without reaching and destroying the bearing) confirms what I’d already suspected: water pump time.

Feel the pump

With the pulley removed, it’s easier to see the pump. You may have to remove all or some of the fan shroud for access.

It’s helpful to crack the pulley’s fasteners free before loosening or removing the belt, as the belt will usually provide the necessary resistance.

In the original application of this car’s engine, the water pump also held the radiator fan, so it uses studs to retain both. Some fans have a large central retainer nut instead — if you have access to an air chisel, special tool kits exist to make removal far easier. Be aware that some central nuts use counter-clockwise threads.


Drain the fluid

Be sure you have all of the necessary tools, seals and gaskets, as well as plenty of the correct coolant, before you start.

You’ll need an appropriate catch basin — coolant should not be drained into the sewer. Any coolant that does spill should be rinsed away with plenty of water. Even with the bittering agents included in most antifreeze, this toxic fluid still smells sweet, and some animals will drink it. I’ve seen the result of this firsthand (a relative’s dog, many years ago), so believe me when I tell you that I would not wish that death on any living creature.

Scrape out the old

As you remove the fasteners, pay attention to their location, as it’s not unusual for them to be of different lengths or sizes. There may also be one or more dowel pins. This particular pump is pleasingly simple.

With the pump removed, you’ll need to prepare the surface. Depending on the style of seal used, this may be very easy (o-rings, sealant) or entirely frustrating (baked-on gasket material). If you have to use a scraper, try not to gouge the housing. If space allows, a drill with a wire brush works quite well at removing old gaskets or sealant and prepping the sealing surface.

Replace the studs

If your pump uses studs, you’ll normally have to transfer them to the new pump. Surprisingly, this original equipment part actually came with new studs, though I still had to install them.

To undo or install the studs, spin a pair of nuts on far enough that the stud is exposed from the outer one, then tighten the outer nut into the inner with a pair of wrenches. This will jam them together, and you should be able to use the outer nut much like the head of a bolt. You can put a wrench between the pilot shaft and stud to hold the flange.

Seal with care

This application uses silicone sealant as the gasket on the pump. Regardless of seal type, surface preparation and cleanliness is crucial to prevent leaks. Do not use household silicone, as it is not intended for exposure to automotive fluids or engine heat. Silicone should never be used in combination with o-ring seals or material gaskets either.

Follow the manufacturer or sealant-maker’s directions for best results, and remember that too much sealant is as bad as not enough. A thin bead on the mating surface and around all fastener holes works best — what’s seen in this photo is bordering on excessive.

Purge the air

Once reassembled and refilled, the vehicle needs to have the air purged from its cooling system; some vehicles have one or more air bleeds for this purpose. A vacuum bleeder or “spill-free” funnel can make this easier.

There should be strong heat from the heater. The upper radiator hose should become uncomfortably hot to the touch, and the electric fan should cycle on at least once (you may have to put the rad cap on to prevent boil-over), with the air pulled through the radiator very hot for at least the first 10-15 seconds.

Be sure to recheck the antifreeze level after the vehicle cools.

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