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Pelican Technical Article:

Replacing Your Water Pump

Steve Vernon

Time:

4 hours4 hrs

Tab:

$50 to $80

Talent:

***

Tools:

10mm, 13mm, 15mm socket, 6mm Allen, flathead screwdriver

Applicable Models:

Mercedes-Benz 300CE (1990-93)
Mercedes-Benz 300E (1990-93)
Mercedes-Benz 300TE (1989-92)
Mercedes-Benz E320 (1994-95)

Parts Required:

New water pump and gasket

Hot Tip:

Work on a cool engine

Performance Gain:

Properly cooled engine

Complementary Modification:

Replace your timing belt

Most water pump failures result in coolant pooling beneath the car, but another sign that the pump is going bad is you'll notice that the car tends to overheat at low engine speed, such as sitting at a stoplight. When you accelerate, the engine temperature will drop. Now, this is not always indicative of a water pump, but a good starting point. You may also want to try squeezing the top radiator hose with the engine warmed up and running (use a glove and watch for heat). You should feel pressure build up on the back of the hose and surge once it is released. If you feel no pressure, it's a fair bet that the water pump is failing.

You will need to begin by safely jacking up and supporting the vehicle, draining the coolant and removing the drive belt. Note: loosen the bolts on the power steering pulley before removing the drive belt. Please see our article on these procedures for further assistance.

Note: there will be several pieces and components missing in the photographs that you will not need to remove. These pieces have been removed for photographic purposes only. You only need to remove what is described in each step. All coolant pump bolts should be checked and be replaced as needed.

Begin by disconnecting the ground cable from the battery.
Figure 1

Begin by disconnecting the ground cable from the battery. Use a 13mm wrench (red arrow). Verify you are working on the negative or ground cable (yellow arrow) and disconnect the cable. Make sure the cable cannot accidentally make contact with the battery ground post while working on the car.

Remove all the coolant hoses from the pump and thermostat (red arrows).
Figure 2

Remove all the coolant hoses from the pump and thermostat (red arrows).

Use a 10mm socket and remove the hard line from the pump (red arrow).
Figure 3

Use a 10mm socket and remove the hard line from the pump (red arrow). Make sure to replace the O-ring on the end of the hard line where it joins the coolant pump.

Remove the two electrical connections on the top of the thermostat housing (red arrows).
Figure 4

Remove the two electrical connections on the top of the thermostat housing (red arrows).

Remove the three 13mm bolts from the power steering pulley and remove the pulley (red arrow).
Figure 5

Remove the three 13mm bolts from the power steering pulley and remove the pulley (red arrow).

Remove the two 13mm nuts and bolts (red arrows) holding the power steering pump and reservoir to the mount.
Figure 6

Remove the two 13mm nuts and bolts (red arrows) holding the power steering pump and reservoir to the mount. Do not drain or separate any lines on the pump. There is not a lot of room to work behind the pump so take care not to drop the nuts on the back of the mount. With the pump loose set it aside with the lines attached.

Slide the locking mechanism on the engine wiring harness (red arrow) open and pull the plug (yellow arrow) from the connection.
Figure 7

Slide the locking mechanism on the engine wiring harness (red arrow) open and pull the plug (yellow arrow) from the connection. You will need the room to get your wrenches in so set it aside in the engine bay.

There are four 6mm Allen bolts holding the coolant pump to the engine block (red arrows, only one shown).
Figure 8

There are four 6mm Allen bolts holding the coolant pump to the engine block (red arrows, only one shown). These are all difficult to reach and you do not want to strip them! I found a long 6mm Allen worked for the bottom and upper rear bolts and an old fashion Allen key worked for the top front bolt. Make sure the Allen is completely seated before you try and break the bolt loose. NOTE: You will need to remove the tensioner assembly to get to that last 6mm Allen bolt.

With the four bolts removed you can remove the pump from the engine (red arrow).
Figure 9

With the four bolts removed you can remove the pump from the engine (red arrow). Even though you have drained the coolant be prepared for a fair amount of coolant co come out of the pump and block.

The area where the pump mounts to the engine can get very dirty and oily; make sure to give it a good cleaning before re-installing the pump (red arrow).
Figure 10

The area where the pump mounts to the engine can get very dirty and oily; make sure to give it a good cleaning before re-installing the pump (red arrow).


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Comments and Suggestions:
EricsinSilverdale Comments: Where do I get the info for a 300d? Eric in Silverdale WA
February 24, 2017
  Followup from the Pelican Staff: You may want to check out our 300TD articles some may apply to your 300D. - Casey at Pelican Parts  
joe Comments: to get to the upper inside bolt you have to go in between the power steering hose with extension where it maxe the curve you have to unbbolt the power steering box first
August 23, 2016
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 
Dray Comments: After further investigation, I found that I have a 13mm head bolt as opposed to the 6mm Allen bolt for that right upper connection on water pump to engine block. Used a small dental type mirror to view. Going to try some type of jointed socket to try and reach from between the header ribs. Doesn't look like much room to enter from below either. Was wondering if anyone here has run into this issue. Very hard to reach with angle and all. Pic attached for small reference. Thx.
August 1, 2016
  Followup from the Pelican Staff: Thanks for the follow up sharing your experience. These type of comments add so much to the Pelican tech community.
- Nick at Pelican Parts
 
Dray Comments: My 1991 300ce's setup is a bit different than the water pump on this car, the procedures for me are more simuliar to the w201 190. The rear upper 6mm bolt on mine is blocked by the manifold. Can you get an Allen wrench in there? The dip stick seems to be in the way also. Thks Nick.
July 29, 2016
  Followup from the Pelican Staff: You may be able to get a long rounded end Allen in to remove the fastener. - Nick at Pelican Parts  
Doug Comments: all due respect to nik who says the tensioner is in the way, its not. you can get the four allen head bolts but you cannot SEE them without a mirror..or by guessing where they are and feeling for them with a wrench. Its a tough job which I did as part of head gasket replacement process. I could not get one of the intake manifold bolts with the water pump in place, just not accessible..I removed about half the tensioner bolts trying for the water pump bolts before finally finding the correct bolts and getting the pump off.
May 18, 2016
  Followup from the Pelican Staff: Thanks for sharing your installation process and experience. These type of comments add so much to the Pelican tech community.
- Nick at Pelican Parts
 
nik Comments: dude you need to remove the tensioner assembly to get to that last 6mm Allen bolt............ You specifically wrote that some things were removed for photographic purposes but 2 days into this shit hole of a job I realise one of the 4 6mm Bolts is literally unreachable cause of the tensioner assemly
January 31, 2016
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. I will have the article updated.
- Nick at Pelican Parts
 

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Page last updated: Mon 5/22/2017 03:08:23 AM