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Replacing the Water Pump

on the 91 300SE (M103)

by sixto


M103 91 300SE water pump replacement pics

The tools I used to remove the water pump: 3/8" ratchet with 6" extension, 3" extension and deep 13mm socket; 1/4" breaker bar with 6" extension, u-joint and 13mm socket. Not shown are a 13mm box wrench and 5mm allen key. Also not shown are the tools needed to remove the serpentine belt, clutch fan, various pulleys, belt tensioner, radiator hoses, thermostat and heater pipe. Other things I don't remember as well.

1/4" socket wrench in action on the rear upper bolt. Viewed from the rear of the engine looking forward. Idle air valve is removed from its mounts but the connections are in place. Dipstick is removed so I can start the bolt by hand.

3/8" socket wrench in action on the rear lower bolt. Viewed from the front of the engine looking back. The water pump hides the 3" extension and 13mm deep socket. It's a straight shot. Nothing fancy. I used a magnetic pick-up tool to set the bolt in place.

Green coolant fill in June 2000 just before I got the car. The head surprisingly looked better. I don't know what it looked like in June 2000. I wish I had descaled it before all the work I just did. It didn't look that bad when I pulled the pump. I scrubbed the orange area with a wire brush then let it sit for a week for an opportunity to continue working before taking this photo.

Fan clutch tool set - 3/8" breaker bar, 10mm deep socket, 8mm allen key. My car has a two-piece shroud so it's off the car. A one-piece shroud would be draped over the fan. Does a 300E have this much clearance between the fan and the radiator? I couldn't get a good shot of the keyway behind the fan pulley. As it is with my car, I can hold the pulley enough to loosen the fan bolt by pulling or pushing on the belt. With the fan and heater pipe out of the way, it's much easier to slip the locking key (piece of stiff wire) into place to remove the four pulley bolts. I forgot to take a picture of the keyway before attaching the heater pipe.

Feeble attempt to show the serpentine belt tensioner scale. It's just to the right of the lower radiator hose clamp bolt. The wide end of the ramp section is clear. The gap and tall section are obscured by the shadow. The pointer is set to the middle of the gap. FWIW, I find it much easier to get the belt in place by releasing the top moung of the tensioner shock. The long hollow nut that takes a 13mm socket is part of the tensioner adjustment mechanism. CW increases tension, CCW drecreases tension. Yes, I'm going to clean the power steering fluid reservoir cap.

I couldn't get a good shot of the 19mm bolt that goes through the tensioner.

Discuss this DIY here.


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