1987 420SEL Water Pump Replacement Questions
 

I woke up to a nice sized puddle of coolant under the front of my 1987 420SEL this morning. Coolant is definitely leaking from the front of the engine, i can't see exactly from where but by running my hand under the pump reveals its wet, so I'm guessing the leak is from the Water Pump.

I looked up the PeachParts DIY water pump replacement article and have a few questions:

1. is there something other than the water pump in the front of the engine that could be leaking coolant?
2. Assuming it is the water pump, what one should i buy? I'm not rich...the prices range from $441 to $84?
3. What else besides the pump should i replace? thermostat, fan clutch, belts, hoses? the belts are 5yrs old and in good shape. hoses look fine.
4. Why do i need to remove the radiator? there appears to be plenty of room to remove the fan, then pull the pump.
5. What else do i need to consider when doing this job?

Thanks, any help is appreciated.

Have you been losing coolant? Is there axial or radial play in the pump pulley?

Sixto
98 E320s sedan and wagon

about 3 weeks ago my coolant level light came on and it was low so i added 1 qt. couldn't see any leaks. then last week it came on again. i parked the car, came out and saw the fluid on the ground. again, about 1qt. Its hard to check for play in the WP with 5belts on there so I'm going to go ahead and just replace the pump and thermostat.

metaprinter, buy a remanufactured water pump from your local MB dealer. You will need to pay a core charge if you do not give them the old water pump. Check the condition of the coolant hoses and drive belts before automatically replacing them. It would be a good idea to replace the thermostat. You should not need to remove the radiator, although I have never worked on a 126 vehicle with a V8 engine. Make sure the O-ring that seals the water pump at the block remains in place during the installation.

UPDATE: In order to replace the water pump on a 420SEL you do indeed need to remove the radiator as well as the distributor and the harmonic balancer...i kid you not. While i was in there i changed all the belts, hoses, thermostat.

metaprinter, it's surprising that MB would design a vehicle that required that much disassembly to replace the water pump ... another reason to avoid buying a MB with an 8-cylinder engine, or at least that vintage MB with an 8-cylinder engine.

I left the dizzy in the 560 when I did the water pump. Somewhere I reported this could be just due to the deck height differences between the M116 and M117. So try doing this without pulling it. Maybe you just need to pop the cap.

Balancer removal IS required. But, while that far in, you should replace the front main too. Thermostat 100%. If your rad hoses are original, swap them. Keep the old two for roadside repair in your trunk tool kit.

Why avoid a V8 MB? The original pump lasted 30 YEARS. I replaced mine when I rebuilt the intake manifold and fixed many oil leaks. Figured prudent while in there.

It sounds much more difficult than it really is to do to this. The balancer is not pressed on, it just bolts to the hub.