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Mercedes Auxiliary Coolant Pump Replacement
 
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Pelican Technical Article:

Mercedes Auxiliary Coolant Pump Replacement

Steve Vernon

Time:

1 hr

Tab:

$250

Talent:

*

Tools:

Wrench, flat head screw driver

Applicable Models:

Mercedes-Benz ML320 (1998-03)
Mercedes-Benz W203 (2001-07)

Parts Required:

New auxiliary coolant pump

Hot Tip:

Replace the pump with the engine cold

Performance Gain:

Proper engine operating temperature

Complementary Modification:

Flush cooling system

Most people do not understand the function of the auxiliary coolant pump and due to its price some people do not replace it when it fails. This is absolutely the wrong thing to do. Most people think that the pumps just circulates water to the heater core to help get heat into the cabin quicker and while the pump does provide this function it also serves as the sole fail safe preventing hot spot or heat soak areas in the engine after it is shut down, that can lead to very expensive engine repair bills. If your pump does not continue to run after you have shut the engine down when it is running hot, then it has failed and you need to replace it before it leads to an even larger problem.

Unfortunately while these pumps are prone to failure, due to the nature of the environment they function, they are very easy to replace.

If you are going to be replacing the pump you might as well replace the coolant as well, as there may be the chance you have "cooked" the fluid if the pump failed. If it is an emergency and you need to get the car right back on the road it is possible to remove the pump without draining the radiator, but you will loose all fluid until the level gets even with the pump. I recommend doing it right and draining the coolant. Even with the coolant drained, you should expect a little spillage when removing the hoses, so be prepared for it.

Begin by safely jacking up and supporting your car. With the car safely off the ground you will need to remove the engine tray. There are six 8mm bolts holding the tray on, the rear two also help hold the transmission tray. If you are going to leave the transmission tray on, remove the rear two bolts first, lower the engine tray, reattach the transmission tray bolts, then remove the remaining four bolts on the engine tray.

With the tray removed you will see radiator drain plug on the lower left front of the car. Place a catch bucket or tray under the plug and use a large flat head screw driver to open the drain plug. The fluid will come out slowly at first so open the tank cap to break the vacuum and help speed things up. The fluid drains out a small spigot facing rearward and not through the red plug.

Begin by removing the right side air intake duct. Simply compress it back towards the engine and slip it off the front air inlet.

The auxiliary coolant pump is located on the front of the coolant tank. It is held in place by a plastic clamp on the front of the tank that holds a rubber isolation band on the pump.

Remove the electrical connection on the top of the pump by pulling it straight back.

Leave the pump attached to the tank and using pliers compress the clamp on the larger hose coming off the pump and remove the hose. If the pump is old you may have to slip a small screw driver between the pump and the hose.

With the larger hose off you can now remove the two other hoses.

You can now slide the pump out of the bracket on the tank and replace it.

Installation is the reverse of removal.

With the car safely off the ground you will need to remove the engine tray.
Figure 1

With the car safely off the ground you will need to remove the engine tray. There are six 8mm bolts (red arrows) holding the tray on, the rear two also help hold the transmission tray. If you are going to leave the trans mission tray on, remove the rear two bolts first, lower the engine tray, reattach the transmission tray bolts, then remove the remaining four bolts on the engine tray.

With the tray removed you will see radiator drain plug on the lower left front of the car.
Figure 2

With the tray removed you will see radiator drain plug on the lower left front of the car. Place a catch bucket or tray under the plug and use a large flat head screw driver to open the drain plug (yellow arrow).

The fluid will come out slowly at first so open the tank cap to break the vacuum and help speed things up.
Figure 3

The fluid will come out slowly at first so open the tank cap to break the vacuum and help speed things up. The fluid drains out a small spigot (yellow arrow) facing rearward and not through the red plug.

Remove the right side air intake to give you more room to work on the hoses.
Figure 4

Remove the right side air intake to give you more room to work on the hoses. Compress it in towards the engine (red arrow) and remove it from the front air inlet.

The auxiliary coolant pump is located on the front of the coolant tank.
Figure 5

The auxiliary coolant pump is located on the front of the coolant tank. It is held in place by a plastic clamp on the front of the tank that holds a rubber isolation band on the pump (red arrow).

Remove the electrical connection on the top of the pump (red arrow) by pulling it straight back.
Figure 6

Remove the electrical connection on the top of the pump (red arrow) by pulling it straight back.

Leave the pump attached to the tank and using pliers compress the clamp (red arrow) on the larger hose coming off the pump and remove the hose.
Figure 7

Leave the pump attached to the tank and using pliers compress the clamp (red arrow) on the larger hose coming off the pump and remove the hose. If the pump is old you may have to slip a small screw driver between the pump and the hose.

With the larger hose off you can now remove the two other hoses (red arrows).
Figure 8

With the larger hose off you can now remove the two other hoses (red arrows).

You can now slide the pump out of the bracket (red arrow) on the tank and replace it.
Figure 9

You can now slide the pump out of the bracket (red arrow) on the tank and replace it.

10
Figure 10

Here is a picture of a new pump

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Comments and Suggestions:
Dave Comments: Do you have the part number for electrical connector for the pump? I'd like to install one in a tractor to supply coolant to the cab heater. Thanks Dave.
December 6, 2016
Shin Comments: Do you sell this Aux water pump in manila philippines? I need to purchase a new unit to replace a broken leaking unit in my c200 kompressor car.
October 12, 2016
  Followup from the Pelican Staff: Should be able to. Give our parts specialists a call at 1-310-626-8765 - Nick at Pelican Parts  
gciccol Comments: Hi Nick, thanks for the feedback. I pulled off the electrical plug going into the pump and checked it for voltage. It was showing 13.5 volts. I then put my volt meter prongs on the two terminals on the pump and did not get any reading, not even continuity. Should the two prongs on the pump at least show continuity with the car running?
Once again, I appreciate your patience and help. Thanks
September 14, 2016
  Followup from the Pelican Staff: Not sure about the pump. If the connector has power, the pump should be oN. sOUNDS Like it is faulty. - Nick at Pelican Parts  
gciccol Comments: Hi Nick,
Thanks for responding to my question. Sorry but I'm just a backyard mechanic.

How do I access the pump to tell if it has power? If I disconnect the wire harness going into the pump and put a volt meter on it should it have a constant voltage reading or only have a reading when it's engaged to run? Also, how do I make it come on? thanks for the help.
September 14, 2016
  Followup from the Pelican Staff: Locate it using the article. Then test at the electrical connector for power and ground when it should be on. - Nick at Pelican Parts  
gciccol Comments: Hello,
I have a 2002 Mercedes Benz CLK320 with an A/C problem. It suddenly started blowing hot air. I ran the DTC codes and received error B1416, Coolant Circulation Pump Malfunction.
Is there a test I can perform on the pump to make sure it is bad? I don't want to buy it and then find out that was not the problem. Thank you for your time.
September 13, 2016
  Followup from the Pelican Staff: Access the pump, does it have power and ground to run when commanded on? - Nick at Pelican Parts  
Michel Harbie Comments: I have a 2002 ML500 and this car I use it in all time hot wether can be eliminate the auxiliary water pump and how? because need replacement can some one help please,thks




















































August 24, 2015
  Followup from the Pelican Staff: We can get you a replacement pump. Give our parts specialists a call at 1-888-280-7799. They can help you find the right part.
- Nick at Pelican Parts
 
duwendag Comments: I have replaced this pump with a 2nd hand pump, the old pump is ok apart from worn brushes, any idea where I can buy new brushes or brushes that can be modified to fit, regards Pete
February 25, 2015
  Followup from the Pelican Staff: No I don't. Try a local electric motor rebuilder. - Nick at Pelican Parts  

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