How do you replace the water pump on a 1999 Pontiac Montana?

REMOVAL:1) Remove the plastic belt routing diagram (there is a bolt underneath if I remember correctly)(yep, 8mm).

2) Using a 3/8 breaker bar or a ratchet, insert into the belt tensioner and push toward the back of the engine enough to release tension on the belt with one hand, and with the other hand, remove the belt from the water pump pulley. Then remove the bar/ratchet from the tensioner.

3) Remove the 4 bolts holding the shiny pulley onto the water pump (11mm).

3a) Large catchpan underneath, there's more coolant in there than it looks like.

4) With a ratchet and possibly a short extension, carefully remove the 5 bolts that hold the water pump onto the block (8mm).

5) Pry the water pump away from the block and clean both surfaces so they are free of gasket material.

INSTALL:1) Line up the gasket and *carefully* fit the new water pump onto the block. The holes are very easy to line up wrong because they are almost, but not quite, equally spaced from each other, so be VERY careful you have all 5 holes lined up right.

2) Screw each bolt in a few tuns to make sure they all go in smoothly. If you get any resistance (it will feel like it's crossthreaded), you have the holes wrong, and you need to rotate the water pump so the holes are lined up right. I can't stress this enough.

3) Torque all the bolts down (I can't recall the exact in/lbs - sorry) in a star pattern.

4) Mount the pulley onto the water pump shaft, torque bolts down (an air ratchet helps greatly here as the shaft will try to spin when the bolts start getting tight).

5) Release the tension as explained in step 2 at the top, put the belt back on the water pump pulley & double check to make sure it's on all the other pulleys while you're at it.

6) Bolt the plastic bolt routing diagram back onto the head.

7) Refill the reservoir and bleed the system of air.

That's it! It's an hour or so job if you've never done it before.

Note, if you're not using a gasket, get some water pump gasket sealer and make a gasket around the entire diameter of the mounting surface of the water pump. Remember to make little circles around the bolt holes also.