Today I decided to repair the Auxillary Water Pump in my wife's 98 ML320. I used this same procedure to repair the E-Box fan in the fuse box on the same vehicle last weekend. It works on 95% of the sealed electric motors I've attemped it on. The pump is designed to run for 10 minutes after the engine is shutdown. It circulates water thru the engine to disipate heat more efficiently. Other MBs have these pumps so see if yours is working and if not, use this procedure to repair it. A new pump costs $220 at the dealer and $160 at independent parts houses. The pump is located on the Starboard (passenger side for you landlubbers) side of the wheelwell on the ML. It sits in a rubber bracket mounted to the wheelwell and is simple to remove. You will need the following tools, 7mm nut driver or a flahead screwdriver, 1/8" drill bit, drill press or a steadly held electric hand drill. A can of CRC 3-36 lubricant/cleaner. Please don't use WD-40 since it contains chlorine. A small piece of air conditioning aluminum tape and finally two small wooden dowels to plug the waterhoses that attach to the pump. Remove the electrical connector from the bottom of the pump by squeezing the two stainless steel clips noted in the attached picture. Remove the two hose clamps using the 7mm nut driver or the flat screw driver. Remove the hoses and plug them with the two wooden dowels. Remove the pump from the rubber bracket by lifting up. Now clean and dry off the electric motor with a shop towel. Drill two small 1/8" holes into the side of the case with your drill press or hand drill. Please be careful to just drill deep enough to break thru the thickness of the case. Remember there's things inside of the motor that don't like to be drilled into. The metal is soft so not much pressure is needed. Once the two holes are drillled where indicated in my pictures, the next step is cleaning the inside of the motor. Take the CRC and insert the spray tip (hold the motor over something that fluid can run into) into one of the holes and hold the motor in your hand with both holes facing up. Fill (and I mean fill up) up the motor with CRC until the second hole starts to discharge dirty fluid. Stop spraying. Now turn the motor over and shake out the dirty fluid. Repeat this process again and continue spraying until the fluid runs clean. Shake the fluid out again. It doesn't all have to be removed since some of it will now lubricate the clean motor. Wipe off the case and stick it back in the mounting bracket and reattach the electrical connector. Turn the ignition switch to the run position for a few seconds and then back to off and remove the key. The pump should now be in the 10 minute run cycle. You should be able to feel and hear it running. If not, don't dispare. Take the nut driver or screwdriver and rap the side of the metal case a few times. 99% of the time this frees up the motor and off it goes. Let it run it's 10 minute cycle so the lubricant does its job. Now remove it and take the aluminum tape and plug the two holes you drilled in the case as seen in the attached photo. Make sure you clean the oil off or the tape will not stick. Now reinsert the motor into the rubber bracket, attach the electrical connector, attach the two hoses and tighten and be happy that you just saved some hard earned cash for about 1/2 hours work.

Here are the photos.

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