BMW E46 Water Pump Failure Diagnosis and Replacement doityourself
BMW E46 (including ZHP) Water Pump Failure Diagnoses and Replacement
Parts required and suggested
• New BMW OEM Water Pump
• BMW Recommended Coolant, (Antifreeze)
• Idler Pulley, these pulleys are lubed when made and never again, good PM
• Tensioner Pulley, these pulleys are lubed when made and never again, good PM
• New Belt
Tools
• 1) Set of 3/8 drive metric sockets. 8mm- 15mm
• 1) Set of metric wrenches. 8mm – 15-mm
• 1) Set of Torx Drivers
• 1) 8 mm Alan Wrench and a 10” piece of pipe to extend it
E46 water pumps can fail in two ways.
In the first case they can leek through the vent hole in the pump. In the illustration above it is very easy to see the vent hole. In the car it’s not as easy as it is located behind the Water pump Pulley.
The second failure is catastrophic as shown in the picture below. In this case the car can no longer move under its own power for any distance without overheating.
What led me to finding my second water pump bad was the Low Coolant indicator light coming on. The cooling system is a sealed system and this light will never come on in less there is a leek. My first step was to add coolant and monitor when it came on again and checking it periodically. There is a float in the expansion tank for the correct level. Be careful not to fill it to the top as I did, my tech told me that could cause the expansion tank to explode. BMW recommended fill instructions at the end of this article. The next thing to do is to do or have a pressure check done. Below is a picture of a pressure checker and the run from $50.00 to $200.00. I personally opted to have my BMW dealer do this for me at a Pre quoted cost of ½ hour labor $45.00.
Once my car was diagnosed by the BMW service facility, and I knew what was needed. I ask them to button it up and put the needed parts and fluid in the car. Note; I do use aftermarket parts on my ZHP, but anything internal to the engine I will only use BMW OEM parts.
Part II Replacing the Water Pump on my ZHP
Before starting the project make sure the car is COLD and has sat for at least TWO HOURS. The Coolant system is under severe pressure when hot. OPINING A HOT SYSTEM WILL CAUSE BURNS TO YOUR FLESH.
First you must remove the air duct form the top or the radiator. This is done by pulling up three plastic pins to allow the expansion pins to collapse and be removed AS SHOWN IN THE PICTURE BELOW.
Next remove the 2 electrical plugs and un-hook the wires from the retaining clip.
Next remove the 2 Torx screws from the top of the fan
Now remove the fan by pulling it in the upward motion
The next thing you will need to do is loosen the four bolts holing the pulley to the water pump. Note; if you forget to do this before removing the belt you will have a heck of a time because the water pump will rotate freely.
Next, pry off the covers on both the Idler and Tensioner Pulleys.
The next step is to remove the belt. The quickest and easiest way to do this is by rotating the tensioner pulley. This is the smaller pulley under the Idler Pulley and above the Power Steering Pulley. Find an 8 mm Allen wrench to fit the bolt in the center of that pulley and a pipe or wrench to extend the Allen Wrench. Rotate it slightly to remove the tension and have a friend remove the belt.
Before you go any further I suggest that you hang a towel over the radiator. This will protect it in the case of a fallen tool or part. It’s bad enough to drop a tool in a place that is hidden or hard to get to but, watching it fall against the radiator followed by a small stream of coolant coming from the point of impact, is by far more irritating and costly.
Once the belt is out of the way remove the 4 bolts holding on the water pump pulley. Next remove the pulley. This can be a little daunting as it is a very tight fit to a flange on the water pump. What I have done that worked, was to tap the front outside of the pulley wile rotating it. Just slight taps because, cocking it too much will cause binding and possible damage to the pulley.
Now you are down to the Water Pump. If you are doing the pressure check and can’t find the leek, this is how far you need to be to tell if the pump is leaking through the vent hole pictured earlier. You may need a mirror to see the vent hole on the bottom side of the water pump. Note; this is how far the Tech at the BMW dealer had mine apart before he gave me the diagnoses that the pump was bad and the area my coolant was escaping from.
To Change the Pump remove the 4 nuts. From here there are two ways of removing the pump. Between the side holes there are 2 metric treaded holes. Matching bolts can be threaded in to these holes that will act as a puller. The method I used was to gently rock and pull the water pump out. At this point the only thing holding the pump in place is a rubber O-Ring. The picture of the new pump below will give you an idea of what is inside.
The next picture shows the engine with the water pump removed.
From this point reverse the process putting everything back together but, don’t fill the radiator until reading that procedure. I may also suggest using Engine Assembly Lube or Vaseline on any metal components that may be a close fit. The items I’m referring to ate the outside diameter O-Ring area on the Water Pump and the inside diameter of the water pump pulley.
After everything is back together similar to the picture below, it’s time to fill the coolant.
Remove the coolant cap and THE BLEEDER SCREW. Failure to remove the bleeder screw will result in air in the system. If this happens the car will overheat.
Slowly fill the expansion tank with specified coolant. According to the E45 Owner’s manual “The coolant level is correct when the upper end of red float is at least even with the upper edge of the filler neck. The end of the float may stick out a maximum of ¾” inch – that is, up to the second mark on the float.”
Note; this is usually mixed 50/50 with water. Having too much water will risk the possibility of freeze up in cold weather or over heating in worm weather. If you want to check how good, or how low your coolant temp is good for you need an Antifreeze Hydrometer and they are available at your local pars store.
Once complete cap off the expansion tank and the bleeder. Start the car and let it heat to the normal midpoint on the data in the car. I suggest only taking the car on close test drives and paying very close attention to the gage on the dash. If it does overheat bring it home and weight until it cools for a few hours before attempting to bleed the system again. This system is under severe pressure when hot. Opening THE CAP WHEN HOT CAN AND WILL CAUSE SEVERE BERNS TO YOUR FLESH.
Good luck,
3ZHPGUY
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Originally Posted by Linh
