Removing water pump, 1999 GMC Jimmy.
Fixing A Coolant Leak:

Replacing A Water Pump On A
1999 GMC Jimmy or Chevrolet Blazer

General Motors 4.3 Liter V6

This Procedure May Also Apply To GM 5.7 V8 Engines


In This Article:

The radiator fan shroud is removed, the coolant is drained, and the serpentine belt is removed. The radiator fan and water pump pulley are removed to expose the water pump. Four bolts are taken out and the pump is removed. The mating surfaces are cleaned up, gaskets are applied to the new pump, and the unit is installed on the engine block.

Related Articles:

Skill Level: 3 (Intermediate) Time Taken: About 4 Hours

By Bruce W. Maki, Editor


This 1999 GMC Jimmy was occasionally leaking coolant. We would see green liquid dripping from beneath the middle of the engine area, just behind the front axle.

Normally when a vehicle is loosing coolant I would crawl underneath the car and look at the bottom of the water pump. There is a weep hole on the underside of the water pump, and when the pump shaft seal starts to leak, coolant can be seen dripping from this hole. BUT... this SUV has a large plastic splash guard under the front of the engine, and I couldn't see anything.

Engine area, 99 GMC Jimmy.

I took a chance that the water pump might not be the source of the leak. But the symptoms pointed to a worn out water pump shaft seal... the leak mostly appeared during the warm-up period. When we checked the coolant level in the reservoir, it would often be down. Yet sometimes the level stayed normal for many days. One time, after a few miles of driving, the car made a 2-foot diameter puddle of coolant on the ground. I decided to buy a remanufactured water pump and tackle the project.

There are other possible causes of a coolant leak: Radiator hoses, heater hoses, the water pump gaskets, a corroded freeze plug, and perhaps even the head gaskets. But from my experience, the most common cause is worn out water pump seal around the shaft. This seal simply can't last forever, and this 9-year-old car had over 155,000 miles on it. Frankly, I was impressed that it took this long for the pump to finally develop a leak.


The Second Time's A Charm...

After I installed this water pump it leaked at one of the gaskets. When I was setting the new pump into place it moved around too much and I had a difficult time getting the bolts started. I suspected that the gaskets might have slipped out of position. After installing the pump I figured out a better method that I could employ the next time I installed a GM pump.

Well... I got my chance when I discovered that the gasket leaked and I needed to remove the pump and install it a second time with new gaskets. I hate doing things twice, but I just consider it a learning opportunity. Besides, I was able to do this job much faster on the second try.


Locating The Water Pump:

The water pump is to the right of the alternator, just below the idler pulley. The red arrow points to the general location of the water pump.


A closer view. The red arrow points to the pulley that drives the water pump. The pump is directly behind this pulley. Location of water pump, GMC Jimmy.


Disconnecting The Battery?

Many service manuals (and the instructions for this water pump) say to disconnect the negatve battery cable to prevent accidental short circuits. This is a good practice, but I didn't follow it because this engine sometimes doesn't run right when the computer loses power. I was extra-cautious about making sure I didn't touch the battery positive terminal while wrenching on things.


Removing fan shroud bolts. Before draining the coolant, I had to find the radiator drain. I couldn't even see the drain plug, so my first task was to remove the radiator fan shroud. There were three screws on the top of the shroud (red arrows), which I removed with a 10mm socket.


General Motors often uses a 2-piece radiator fan shroud. There were 2 screws on each side of the shroud, about a foot down from the top (arrows). Fan shroud, lower side bolts, 99 Jimmy/Blazer.


Lifting out the radiator shroud. To remove the shroud, I had to lift the air conditioning hoses up with one hand and carefully pull the plastic shroud up and out. The first time I removed the pump I had to bend these hoses pretty badly, which made me uncomfortable. Air conditioning hoses are known to leak after a decade or more, because the material degrades over time. Flexing the hoses severly can't possibly be good for them.


For my second attempt, I unbolted the air conditioning compressor and raised it up a couple of inches. When I removed the upper fan shroud I was able to lift the a/c hoses out of the way without kinking them, and it was much easier to get the shroud out.

Read the article about moving the a/c compressor.

Note that most of these pictures were taken during my first attempt, so there are some inconsistencies, such as the a/c compressor and serpentine belt appearing installed after another article says they were removed.

Lifting out the radiator shroud, a better way.


Upper radiator shroud, 99 Jimmy/Blazer. The upper shroud. Note the locations of the side fasteners (red arrows).


With the upper shroud removed, I had better access to the radiator fan and water pump pulley. Radiator fan, 99 Jimmy or Blazer.


Removing The Serpentine Belt:

The serpentine belt is removed by rotating the automatic tensioner and slipping the belt off the easiest point, which is the idler pulley.

Location of tool socket, automatic belt tensioner.

There is a 3/8" square hole in the automatic belt tensioner (red arrow).


To rotate the tensioner, I inserted a 3/8" drive ratchet into the square hole and pushed the ratchet to the left (arrow). Then I slipped the serpentine belt off the idler pulley.

I found it best to start with the ratchet handle straight up, because when the belt is removed the tensioner will rotate back, and the wrench handle can hit the water pump pulley, making it impossible to remove the wrench.

Removing serpentine belt, loosening the belt tensioner.

After removing the belt, I realized that it might help to have the belt installed to hold the pump pulley while I loosened the bolts, so I put the belt back on. Since this job I have done this procedure without the belt in place. Holding the pump pulley stationary is the tricky part, but there are several ways to do that.


Removing The Radiator Fan And Pump Pulley:

I figured that it might be easier to loosen the pulley bolts if I held the fan with a large wrench. The fan shaft is a large hex nut. My big adjustable wrench was too wide, so I used a 1-1/2" open-end wrench (arrow "A").

(This might be a metric fastener, perhaps 36 or 37mm. A 1-3/8" wrench was too small, and the 1-1/2" wrench was a bit loose, but it worked anyway.)

To loosen the four bolts, I held the fan with the big wrench and loosened the pulley bolts with the 13mm box-end wrench (arrow "B").


Once the pulley bolts had been loosened, I held the pump stationary by placing the smaller wrench (B) across two bolt heads and turned the large wrench (A) counter-clockwise to loosen the fan shaft.

(The fan has a normal right-hand thread.)


Removing radiator fan, GMC / Chevy truck.

Then I unscrewed the fan shaft from the pump shaft.

It was kinda hard to turn the hex shaft by hand, and using the wrench was awkward and slow.

After I removed the fan and pulley, I removed the serpentine belt again.

With the fan out of my way, I removed the bolts that held the water pump pulley to the pump shaft.

You can see a set of four small holes in between the pulley bolt holes. I suppose I could have inserted some special tool in these holes to hold the pulley stationary while turning the pulley bolts... but I didn't have anything like that.

Removing water pump pulley bolts, General Motors truck.


Prying pulley off.

The pulley wouldn't come off easily because there was some corrosion around the inner hole. I inserted a pry bar behind the pulley and pulled in the direction of the arrow, and the pulley came off.


Once the pulley was removed, I had access to the four bolts that held the water pump to the engine block. Water pump and pulley.


Water pump, 99 Jimmy or Blazer. The water pump (red arrow) is cast iron, so it's easily identified by the rusty color.



I removed the lower shroud by inserting a screwdriver into each of three plastic tabs and rotating the screwdriver to push the wedge-shaped tab towards the front of the car. Then I pulled the shroud upwards. In spite of my caution, I still managed to break the middle tab.


Finally... Draining The Coolant:

The radiator drain valve is a couple of inches above the bottom of the radiator, on the passenger side of the car.

I inserted a 1/4" drive ratchet into the center of the drain valve and loosened it about a half-turn. The center of the valve moves outward as it turns, and then coolant flows out through a drain hose.

Draining coolant from radiator, 1999 GMC Jimmy or Chevy Blazer.


I placed a dishpan under the front of the car to catch the coolant that flowed from the drain hose.


A Closer View:

The drain hose (red arrow) is visible just to the left of the passenger-side tow hook.

Radiator drain tube location, Jimmy/Blazer.


Notes On Draining Coolant:

When closing the radiator drain valve, you need to push it inward and then tighten it. When fully closed, there is a small tab on the off-white center part that engages a slot in the black outer part.

After the water pump is removed and all the coolant has drained, I recommend closing the drain valve before putting all the parts back on the car. If you forget to close the drain before replacing the fan and radiator shroud you'll regret it, because a simple 2-second task can become a 10-minute ordeal. I made this mistake the second time I installed the pump.

The drain valve on the Jimmy/Blazer is really difficult to reach when the radiator shroud is in place. There is barely enough room to get your hand down to the drain valve, and then the 1/4" drive ratchet doesn't have much room to turn. A couple of short extensions on the ratchet make it possible, but you can't see the square hole in the drain valve, so getting the extension engaged in the valve is not easy. I won't make that mistake again.


I discovered that it's best to remove the heater hoses from the pump BEFORE removing the lower radiator hose. When the heater hoses are removed, air enters the cooling system and lets more coolant flow out the drain plug.

I removed the idler pulley to make it easier to reach the heater hose connections behind it. Removing idler pulley, GM 4.3 liter V6 engine.


Removing heater hose. Using a pair of Channel-Lock pliers, I loosened the spring clamps on the heater hoses and moved them away from the ends.


Cooling system hoses often won't budge until the rubber is separated from the metal. I inserted a curved hook tool between the hose and the metal tube to loosen the hose.


Removing lower radiator hose, GM 4.3 liter V6.

I couldn't get the lower radiator hose off, so I made a slit in the end (red arrow), and then it came right off.

I had already bought a new radiator hose anyway.

Replacing Hoses?

If the hoses are more than 5 or 6 years old, I prefer to install new radiator hoses when replacing a water pump or radiator. If I notice cracks in the rubber or swelling around the ends, I just replace the hose.

The radiator hoses looked decent on this 9-year-old car. Replacing the upper radiator hose would be simple, but reaching the lower hose later would be quite difficult. So I spent 14 bucks and bought a new hose from my local NAPA dealer.


Removing The Water Pump:

Simply finding the bolts on this water pump wasn't easy because there are so many accessories around it.

Water pump bolt locations, GM V6 or V8 engines. The left-side bolts are beneath the alternator, and directly above the lower radiator hose connection.


The right-side bolts are beneath the bracket that supports the air conditioning compressor and the power steering pump.

(You can't actually see these bolts like the photos show, unless you have removable eyeballs. I placed my tiny camera behind the radiator and shot these pictures.)

Water pump bolts, GMC Chevy truck .


Water pump bolt locations, GMC Jimmy, Chevy Blazer, GM truck.

The normal view of the water pump. The arrows show the bolt locations.

Take a look at those two previous close-up pictures, and notice how the bolts are just above and below a "post" that is cast into the pump housing. This is important, because once the job is done, these bolts need to be re-tightened after the engine has warmed up. There is enough room for a ratchet and socket, but you can't see 3 of the 4 bolts. You can see those "posts" (barely), and then you can feel around for the bolts.


I removed the water pump bolts with a 14mm socket and extension. Removing water pump mounting bolts, GM truck.


I couldn't reach the bolts with my fingers, so I used a magnetic parts-picker-upper tool to pull the bolts out once they were unscrewed all the way.


With all the bolts removed, I inserted a pry bar between the water pump and the engine block. I pulled the pry bar in the direction of the arrow. Prying water pump from engine block.


Then the pump just fell off.


I scraped off the gasket with a razor-type gasket scraper. Scraping old gaskets from engine block.


Cleaning mating surfaces with die grinder, 3M Roloc disc. I used a right-angle air die grinder with a 3M Roloc abrasive disc to clean up the mating surfaces on the engine block.


Clean mating surfaces will ensure proper sealing of the water pump to the engine block.

Both of the top holes are "blind holes" (they don't go anywhere), so I used compressed air to blow the debris out of them. The lower holes are "wet holes", meaning that the bolts go into the cooling passages. I cleaned these threads with a Q-tip and brake parts cleaner instead of compressed air.

Water pump mounting surface, GM truck.


Water pump bolts.

Prepping The Bolts:

The water pump instructions said to use thread sealant. The original bolts appear to have some type of thread sealant about 1/2 inch from the end. I traced the outline of one bolt and marked the area that had thread sealant. Why?...


...Because I cleaned the bolt threads on a wire wheel mounted to a bench grinder.

Be careful if you do this... and wear eye protection. This thing throws junk in your face.

Buffing bolts to remove dirt and rust.


Remanufactured water pump from NAPA, part 58-521.

This is the remanufactured water pump from my local NAPA store, which cost $38 plus a $9 core deposit. Their part number is 58-521. This pump also fits General Motor's 350 cubic inch V8 engine.

This part is made of cast iron and has a rust-inhibiting coating. The mating surfaces didn't look very smooth to me, so I used a piece of fine sandpaper and a flat wood block to sand down the mating surfaces. Then I could see what appeared to be lumps of this black coating on the surfaces, so I used the die grinder and Roloc disc to remove all the coating, leaving the mating surfaces bare iron.


The gaskets provided were oversized. I cut off off the excess with a pair of scissors. Trimming gaskets.


Applying gasket sealant to gaskets. I applied a bead of Permatex Form-A-Gasket sealant and spread it with a putty knife.


I also applied the same sealant to the mating surfaces of the pump. Applying gasket sealant to new water pump.


Then I placed the gaskets on the pump mating surfaces. There is sealant on both sides of the gasket.


I appplied a small dab of Permatex High Temperature Thread Sealant to the area of the bolt threads where the original sealant was located.

The instructions say to only apply the sealant 3/4 of the way around the outside. I'm suspicious of this advice... when I removed these bolts later it appeared that the sealant may not have spread very well.

I smoothed out this goop with my finger before installing the bolts.

Applying thread sealant to water pump bolts.


Installing The Pump - First Attempt:

I positioned the pump and installed the first bolt, using a 14mm socket and extension to turn the bolt by hand until it was almost tight..

THIS WAS NOT EASY. Some water pumps have a pin that goes into a hole in the engine block, but not this one. As I struggled to hold this heavy part and get the second bolt started, I realized that the gaskets could be sliding around and I couldn't see the lower end of the gaskets to be sure they were still aligned. It was hard enough to see the top of the gaskets, even with three bright lights that I used for photography.

The second bolt I installed was the top-left bolt. Then I got the lower-right bolt started, but the lower-left bolt just turned endlessly without the threads engaging. I figured the gasket had slipped aside, so I inserted a tapered alignment punch into the hole with the hope that the gasket would slide over inspite of the stickiness of the sealant.

It worked... I was able to get the fourth bolt threaded into the hole. Then I tightened all of the bolts in a cross-pattern (such as upper-left, then lower-right, then lower-left, and finally upper-right). After they seemed tight (I don't know what the torque specification is), I tightened them again. This is a cast iron pump and a cast iron engine block, so the bolts should be able to tolerate considerable torque. But... too much torque might make the gaskets squeeze out.


Second Attempt...
Making It Easier To Guide The Pump Into Position:

When I removed the pump after my first failed attempt, I grabbed an ordinary 3/8" hex nut to see if it would thread onto the pump bolts. Wahoo! It did. I was relieved, because I thought these bolts might have a metric thread, meaning I would need to run out and buy some sort of metric bolt to use for my special trick. Since an ordinary 3/8-16 bolt would screw into the bolt holes, I could use some fasteners from the supplies I keep on hand.

I cut the heads off a couple of 2-1/2" long 3/8" bolts.

I used an abrasive cut-off saw, but these bolts can be cut with a reciprocating saw and a metal-cutting blade, or just a hack saw.

Guide pins for installing GM water pump.


Pump guide pin theaded into engine block.

Then I screwed the cut-off bolts into the lower bolt holes in the engine block.

To make them easy to remove, I only screwed these in a couple of turns, until they didn't wiggle too much.


To make a better seal, I applied some gasket compound around the underside of the bolt heads. I only did this for the bottom two bolts, because the top bolts don't go into the water jacket. I did this extra step because I figured that if the thread sealant leaked, this might prevent coolant from leaking out around the bolt head. Also, this might prevent a leak if the gasket leaks between the lower bolt and the cooling passageway.

When I applied thread sealant the second time, I smeared it closer to the end than the first time, and I applied it all the way around the thread, not just 3/4 of the way.


Installing water pump, GM truck.

With the new gaskets stuck to the pump, I slid the pump into place. It wasn't easy to get the bottom holes aligned with the guide pins, but this was better than my first attempt to install the pump.

Then I started the top bolts into their holes.


I tightened the top pump bolts as far as I could, by hand, and then I removed the guide pins.

I couldn't unscrew the pins by hand, so I used a pair of needle-nose vice grip pliers to remove the pins.

Removing guide pin with vise-grips.


Once the guide pins were removed, I installed the bottom bolts. As shown earlier, I applied to thread sealant to the bolt and gasket compound to the underside of the bolt head. I tightened the bolts by hand (meaning that I used a 14mm socket and extension to turn the bolt) and then I tightened the bolts with a ratchet. As with any component that is attached to an engine block, I tightened the bolts in a cross-pattern.


The heater hose connections had a sticky coating on them, so I sprayed some brake cleaner on a paper towel and wiped the coating off the ends of the tubes. It would've been easier to do this before installing the water pump, but I forgot.


I installed the heater hoses. To make it easier to push the hoses onto the tubes, I wiped the inside of the hoses with a wet paper towel.

I used new worm-type stainless steel hose clamps instead of the original spring clamps.

I've read that the original hose clamps, which are known as "constant force" clamps, are a better choice, but when I installed the left-hand hose I noticed that it would turn without much effort. I figured this hose connection might leak, so I used a worm-type clamp.

The rubber at the ends of the hoses got squashed from the original clamps, so the diameter was slightly less. Besides, the original clamps may "take a set" and not return to their exact diameter after being removed.

The problem with worm-type hose clamps is that they are very easy to over-tighten, which may cause the hose to deteriorate faster. If the metal band is cutting into the rubber, it's TOO TIGHT.


I installed a new lower radiator hose (NAPA part no. 8723), but I used the original hose clamps.

The old lower radiator hose looked the worst of all the cooling system hoses, and I figured it would be the most difficult to replace later, so I bought a new one for about $14.

Installing hose clamps.


I cleaned the oil and dirt from all the drive pulleys with brake cleaner on a paper towel, using a small flat screwdriver to force the towel into the grooves.


I replaced the serpentine belt idler pulley and the water pump pulley.

To tighten the pump pulley bolts, I used a medium-sized prybar to hold the pulley from turning, while tightening the bolts with a 13mm box-end wrench.

Since this is a rotating part, I tightened the bolts in a cross-pattern.

Then I replaced the serpentine belt. I would normally take this opportunity to replace the belt with a new one, but this belt was only a year old, so I re-used it.


I installed the radiator fan. To keep the pulley from turning, I wedged a wrench across two of the pulley bolts, then I used the big 1-1/2" wrench to tighten the fan shaft.

This took some careful manuevering to avoid bending the plastic fan blades. Breaking a blade would be a bummer.


I installed the screws that held the radiator top shroud to the car body.


After making sure the radiator drain plug was closed, I filled the cooling system with coolant.

I used a long skinny funnel to avoid spilling coolant. The radiator cap is on an angle, and my larger funnels wouldn't fit. This cooling system filled more slowly than other vehicles I've worked on.

Adding antifreeze coolant to radiator.

Once the radiator was filled with coolant, I started the car, made sure the climate control was set to "heat", and ran the engine until the temperature gauge reached about 190 degrees and the thermostat opened. Then I checked the coolant level in the radiator (it had gone down) and added more coolant.


Checking For Leaks:

As I mentioned at the beginning, the water pump leaked when I first installed the new pump. After warming up the engine, there was a 6-inch green spot on the snow in my driveway. The spot was directly beneath the right-hand pump gasket. When I examined the engine, there was steam rising from that area.

The instructions say to tighten the water pump bolts again after the engine had warmed up, which I did. It wasn't easy getting a socket and ratchet into the space between the serpentine belt and the radiator fan, and I had to feel around for the pump bolts. They definitely needed more tightening. But the pump still leaked. Bummer.

The next day I tore everything apart again, bought new pump gaskets, and installed the pump again using the guide bolts and other techniques mentioned above. The job went much faster the second time. We'd got about a quarter-inch of snow the previous night. When I backed the car out of the garage and let it run, there was a green spot on the snow. Double bummer. After the engine warmed up I re-tightened the bolts and drove the car to the store to buy some beer. I certainly didn't want to do this job a third time... I figured I wait a couple of days and buy one of those cooling system leak-stop products. When I returned home I parked in a different part of the driveway. I never saw any more green spots on the snow.

The point is: Don't be fooled by antifreeze spots on snow. The spot underneath the car after my second attempt was from the previous day. Even though we had some fresh snow, snow falling on antifreeze will melt, just like snow falling on salt.


Air In The Cooling System:

Often after filling the cooling system it's necessary to "burp" the cooling system to get rid of any pockets of air. This can be done by running the engine for a few hours (or even a few days) with the radiator cap turned to the "first notch" which simply holds the cap in place while not forming a tight seal. Turning the radiator cap to the "second notch" forms the tight seal needed for proper pressurized operation.

The Jimmy didn't seem to need any special burping procedures... I just ran it until the thermostat opened, added coolant to the radiator, and then topped up the coolant in the reservoir.


Antifreeze/Water Mixture:

While most mechanics recommend using a mixture of 1/2 antifreeze and 1/2 water, I use 2/3 antifreeze and 1/3 water, which has a substantially lower freezing point (about -60 F versus -35 F). Here in northern Michigan the extra protection can be worthwhile.


Wintertime Cooling System Repairs:

Getting the air out of the cooling system requires running the engine until the it gets hot enough for the thermostat to open. In the winter months, sometimes the engine never gets warm enough for the thermostat to open, especially when just idling or driving gently around neighborhood streets. To make the engine warm up quicker, I put the transmission in gear and held one foot firmly on the brake pedal while revving the engine with my other foot. (I guess they call this a "brake stand".) BE CAREFUL if you do this. I put the car in reverse, so if my foot slipped off the brake pedal I wouldn't crash into my garage door. A smart person would put wheel chocks behind and/or in front of the tires.

Beware... excessive "brake standing" might overheat the automatic transmission fluid. By the way, you can't do this with a manual transmission.

Another pointer: If the car has air conditioning, set the climate control to defrost. Most vehicles will run the air conditioning system when the defrost setting is selected, even if the temperature control is set to maximum heat. By cooling and heating the air, moisture is extracted, just like a dehumidifier. When the a/c runs it taxes the engine and causes it to warm up faster. I always run the defroster after I start my vehicle in cold weather.


More Info:

Tools Used:

  • Flat Screwdrivers, Small, Large
  • Sockets: 10, 13, 14mm
  • Wrenches: 5/16", 13mm, 1-1/2"
  • Right Angle Die Grinder with Roloc Disc
  • Air Compresor
  • Air Blow Gun
  • Putty Knife
  • Scissors
  • Curved Hook Tool
  • Bench Grinder with Wire Wheel
  • Plastic Dishpan
  • Funnel

Materials Used:

  • Remanufactured Water Pump, NAPA Part No. 58-521
  • Water Pump Gaskets (for the 2nd repair), NAPA Part No. 5152
  • Lower Radiator Hose, NAPA Part No. 8723
  • Permatex 1A Gasket Compound
  • Permatex High Temperature Thread Sealant
  • Brake Parts Cleaner
  • Antifreeze (About 1 Gallon)
  • Water

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Written March 5, 2008