Om651 (x218 cls250cdi)

[garethbevan59]

Hi guys I'm experiencing some weeping from the water pump and a bit of play from the bearing so I plan to remove and replace. I will be buying the water pump from Mercedes as they offer a recon unit with 2 year warranty. I need some advice please...

1. Is this an easy job to do?
2. Are these engines hard to bleed the coolant system.
3. When refilling the coolant system does it require vacuum refilling or is it ok just to pour in as normal
4. How many litres of coolant do I need
5. Can I buy coolant other than the Merc stuff what is it I actually need

Any other tips/advice/pitfalls please share

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[MinionBob]

Easy job on my 651. No majors. No problem bleeding the system ( I have done it twice), just stick it in. I elected to buy backwards-compatible coolant, and flush most of the old stuff out.

It perplexes me why mfrs keep coolant specifications in particular such a secret..

 

[garethbevan59]

Thanks Bob, I bought the water pump from Merc today along with coolant they recommended 2 bottles (3ltrs) and mix accordingly due to our climate no need for 50/50 ratio - the new pump assy is metal one rather than plastic did you do the job from underneath?

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[MinionBob]

The 651 engine can be mounted in different ways; transversely or longitudinally; I think mine is longitudally mounted so the pump is just bolted to the front of the engine, making everything accessible from the front, top (bled screw for rad on bottom, RHS when viewed from front, screw is coloured red.)

No drama's; basic home mechanics toolkit will suffice.

 

[garethbevan59]

Thanks yeah mine longitudinal also so pump 12oclock top on front of engine thanks again for your input

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[Uncle Benz]

They can occasionally be a swine to bleed out. I have a clever vacuum unit which sucks the cooling system to a high vacuum, then open a tap and draw the coolant in. You can do without, but when you have filled the cooling system be prepared that you might see a sudden rise in coolant temp. If you do, stop, allow to cool and then top up the header tank. In most cases just the one stop and top up will do the trick, but be aware that they can air-lock and need that one big gulp to get the air out. The in car heater is often a good barometer. If the heater gets hot you usually have all the air out. If it won’t get hot there is invariably air trapped in the system

 

[steveq]

I have heard that if you have the car on a slope with the front higher when you do the job and then put the new coolant in, it won't get airlocks.
I replaced my S212's water pump with the car like that and didn't get any airlocks but of course who knows if it actually made any difference.

There is a good video of a German mechanic doing it on a C Class with the OM651 engine. It is well worth a look prior to doing the job.