m103 water pump
 

Having trouble with water pump leaking where the pump connects to the cylinder block. I removed the pump and replaced the o-ring. It's leaking still. Removed the pump again, and added some RTV on the outer surface and its still leakin. WTF? I bought 3 of those o-rings just in case so I can remove pump and do it correctly, but what am I missing?

Look very closely at the back of the pump...IIRC mine looked as though it was the pump to block o-ring but it was the cover on the back of the pump. Had to replace the pump.

Good luck!!!

If you put sealer on like i do for insurance .The i would say coolant leaking from some other part of the pump ...did you put some sealant in to the bolt holes . ?

I've done more than enough of these to know that when they leak out of the weep hole, as they should when worn, the coolant rolls back and drips right where it mates to the block which makes it appear to be a leaky o-ring. Me personally, out of the hundreds that I've done, I've never seen a leak at the o-ring unless it was installed wrong.

New water pump was installed 2/2016 and is still under warranty. Sending it back and getting a replacement shipped. Cheers!

Original MB?

No, Laso brand.

Please post the solution/close the thread. Thanks!

m103 water pump: RESOLVED
 

New water pump installed and used JB weld blue RTV around mating surfaces. No more leaks. Although, now I suspect the problem was not the water pump failing, possible just a bad seal.

ismalley Good job done . I know others dont like the use of sealant .But at the end of the day those people dont have to remove it again to seal it up .

Here's one I did.
https://farm4.staticflickr.com/3032/...51e_z.jpg?zz=1

You really need the area and the little channel the seal fits in thoroughly cleaned before installing a new seal and the pump.

MB actually advises not to use any sealant on the O ring. I use sealant but very, very sparingly.

Most ongoing leak issues were caused by el cheapo pumps not being machined properly.

Use only Laso or Graf pumps.

Changing a M103 pump is a frustrating job. You only want to do it once.

Elcheapo pumps use inferior plastic impellers.
When the pump itself leaks there is evidence such as :
https://farm4.staticflickr.com/3339/...36e8cd39_o.jpg

Yes, the original pump I had installed 2 years ago was a Laso. I did not see any signs of the drain hole weeping, but it was still under warranty so I had them send out another one. Ans yes, this is a job you do not want to do twice. Unfortunately for me I ended up removing and installing the WP 5 times until I finally took the Laso off, put on the spare one I had and used sealant on it. No more leaks. Sent the Laso back and got another one, used sealant on that and now I'm good to go. This is something I do not want to have to worry about during the summer

Installing the WP 5 times. 😩😩
I feel your pain😱
This is a job you want to get right the first time around. Its easy to foul up the belt tensioner and you need to remove it to get to the water pump.
m103 WP relacement has got to be one of the worst MB pitfalls

Glad it is done!!!

You must be getting good at changing them. What was your best time?

I did that too, kind of. Put a warrentied pump in and it squeeled. They said "no problem, just send it back and we'll send you a new one." I disagreed with their "no problem" part.