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Old 09-05-2003, 12:08 PM
Registered User
Join Date: Sep 2003
Location: Florida
Posts: 24
coolant leak

found coolant leak when changing oil. it drip down side of oil pan from back of water pump. anything to look for before pulling pump?
please advise how to remove water pump if I need to and tools needed.
forgot 1988 300SE
thanks brian
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Old 09-05-2003, 01:42 PM
sixto's Avatar
smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 18,745
Yup, that's the pump. Leaks out the weep hole on the lower side of the snout behind the pulley, down to the bottom of the pump flange, along the side of the block and to the ground in the area of the motor mount.

Lots of info on M103 water pump replacement in the archives but in a [coco]nutshell:

- drain coolant
- remove or release shroud
- remove fan; easier with belt on and tight; 8mm allen in front of fan
- loosen water pump and power steering pulley bolts
- release tensioner tension
- remove belt
- remove water pump and power steering pulleys
- remove tensioner
- shove the power steering pump aside
- loosen the clamps on the stubby bypass hose; consider replacing this difficult-to-replace hose
- remove thermostat
- remove the heater pipe that goes across the front of the engine
-- 10mm hex head bolt on the water pump
-- 5mm allen head bolt behind the fan pulley
-- hose clamp to the right of the AIR pump
-- you'll probably need a new o-ring
- remove water pump
-- one allen head bolt in upper front, the rest are 13mm hex head
-- the upper rear one is accessible with a 1/4" drive socket on a u-joint with a 6" extension and easier with the dipstick out of the way (13mm head bolt into the intake manifold, then yank out the tube, watch for the o-ring, plug the dipstick hole so you don't get coolant in the sump). Alternatively there's a Snap-on tool that works perfectly - check the archives for the part number.
-- the lower rear one is accessible with a 3/8" drive socket with a 12" extension from behind the power steering pump

Installation is the reverse but put a dab of grease or sealant on the water pump o-ring so it stays in the groove as you wiggle the pump into position. And for heaven's sake don't forget to have the stubby hose and clamps in place before you install the new pump.

This is from memory so I might have missed a few things.

Good luck.

95 S420
91 300SE
87 300SDL
83 300SD
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