The pump itself is a snug fit to the housing. The combination of the tight fitting pump and corrosion can cause the pump to weld itself to the housing and refuse to break loose, making removal of the pump and housing together a better choice...especially if you don't have ready access to a replacement housing.

So it might be easy to get just the pump out, or it might be necessary to take them both out and separate the pieces on the bench. This has happened to me more than once. The latter case obviously entails more work.

If the housing has to come out, use some extra caution when loosening and re-tightening the banjo bolts for the vent line between the housing and head. It kinks very easily. Or, plan for it and get a replacement ahead of time, since it's probably been clogged up for a while.

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'79 240D

I agree.

And, besides that this thread is about replacing a Water Pump and we are not talking about chasing threads on main bearings or cylinder heads or other threads where strength is important.

I just changed the Water Pump on My Car and the OP had brken off one of the Blots an unknown length of time ago. I did not drill it out and just like the single broken Bolt cause no issues with the previous Water Pump I am not expecting any with the new Water Pump.

I chased the internal threads with a cheapie Harbor Freight Tap as I did not have a better quality one in that size.

It is common to sear off Water Pump Bolts and also Bolts on the Water Pump to Block Housing

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84 300D, 82 Volvo 244Gl Diesel

Stripped Water Pump Bolt Threads
Water Pump - Mercedes-Benz Forum

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84 300D, 82 Volvo 244Gl Diesel

Thanks for the info, everyone.

This turned out to be a complete non-issue. All five water pump bolts SEEMED stuck at first, but once I cracked them loose, all five unthreaded easily and cleanly.

I learned a few things:

1. The last person who replaced the water pump gave the bolts a light coating of what looked like white lithium grease, which kept them from seizing
2. The water pump that came out was a genuine Mercedes part (had a Mercedes star stamping), but I doubt it was original to the car
3. I'm not sure, but I think the bearing was starting to seize up. It didn't turn as smoothly as I would have expected. I'll compare it to the new pump when I have that in hand.

Incidentally, the thermostat housing bolts also backed out easily, though they had been put in dry. Honestly, I was expecting a terrifying ordeal from these eight bolts (I never did a water pump on a Mercedes before, but I've replaced thermostats, and have ALWAYS had trouble with the bolts on the thermostat housing).

Much of the problem has to do with whether or not the coolant has ' access' to the bolt on the inside of the cooling cavity... if so... sure needs some kind of thread protection for the next time they need to come out...

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

If the pump was leaking out of the weep hole, the bearing likely is seizing up. The bearing is protected by the seal which holds back the coolant from contaminating it. Once the seal wears out, coolant gets into the bearing and causes it to seize. The weep hole let's this leaking coolant run out so you are aware of the situation and replace the pump.

My water pump bolts came out easy as well (although that's on a 601, totally different). I was very pleased.

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'84 190D 2.2 5MT (Red/Palomino) Current car. Love it!
'85 190D 2.2 Auto *Cali* (Blue/Blue) *sold*
http://badges.fuelly.com/images/sig-us/302601.png
http://i959.photobucket.com/albums/a...0/sideview.png

It wasn't leaking that I know of, but in over 3.5 years, I've never driven the car more than in and out of my own garage. Before that, it sat in the previous owner's garage for around five years before I bought the car. I doubt the pump was new at that time. At any rate, I have no idea how old the pump is, and am replacing it for preventive reasons.