My 95 E320 is coming up on 113K. I've had the car since 52K with no records before that, so I assume the water pump is original. I'm curious if now is a good time and if it's wise to replace the water pump before it goes out on me at some inopportune time. I take the car on 200 mile trips during the summer, and I'd hate to be stranded because of a water pump that decides to leak. The convertible is retired for the winter season for about another month or so, so I can do the job at a leisurely pace.

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95 E320 Cabriolet, 159K

They can go at any time, but I had one car that had 300k on the original WP. If you're worried about it change it. If you do it your self, it's not a great deal of money. From my limited experience, WPs usually start to weep before leaking badly allowing you to get home. So getting stranded is not too likely.

I thought there was some predictable timeline for water pump failure. I'm borrowing my thinking from the engines that have timing belts, where it is commonly prudent to change the water pump along with the timing belt. With my limited experience, once the water pump starts weeping, it becomes a gusher rather quickly, within 50 miles.

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95 E320 Cabriolet, 159K

I tend to " life " parts as I'd rather change them on my schedule and not at random.

113 K is well within in the failure window, I bought my 97 SL320 at 124 K and the pump was starting to leak.

When you do the pump, change as many hoses as possible. I bought all of the hoses at the dealer and the pricing was what you would expect for a Chevy at a generic auto parts. The limiter here is that I deleted the expensive looking heated window washer tank and windshield molded " T " hoses as my car is summer only. Talk to the dealer parts guy, many times they can put your order under a garage discount if you look the part and order a pile of stuff.

I also added a second valve to the heater core so it does not get hot under the dash. The SL heater core has large in and out hoses plus a small bleed line, this bleed line allows coolant to circulate even when the stock valve is closed.

Also get a grease needle and lube the idler pulleys with one pump, this will keep them going. ( Don't put in too much grease, the added friction will burn the grease causing it to degrade. )

Water pumps don't usually "suddenly" fail....they start to rattle and leak for a few thousand miles first...

My 300E M103 has the original pump working fine with 163k on it....if it was a car I drove on multi hundred mile trips all the time, I'd probably change it, but since it rarely goes more than an hour away, I'll wait till it shows signs of failure.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Failure progression rate varies. If the bearing starts to fail, it can allow the seal to lose contact resulting in a slow leak but that is only one failure mode.

All modern water pumps use a spring loaded face seal. Many have a rubber diagphtam that once it tears, complete failure is rapid. If the rubber ring around the seal seat degrades, the leak will start out slow and slowly get worse.

In short

m104s fail about 212,000 miles

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

Both my Dad's 1995 M104 water pump and my M103 water pump failed at about 170K mi here in FL. Based on that and my current practice of driving more on long distance trips I replaced my M112 pump at 170K mi. I used a dealer rebuilt pump on the M103 and Grafs on the M104 and M112. No problems with any of them. I would much rather replace a part like this at my convenience than have to deal with the headache and cost of replacing while on a trip. Further, if the pump should manage to fail suddenly you may miss the high temps and fry your engine. Just my $02. It's interesting that years ago (60's in my personal experience) MB would specify replacement schedules for major components such as water pumps, generators and suspension components. IIRC the W112 300 series air suspension bellows were to be replaced at 100-110K kms with a set age limit as a kicker. Sure, you could get a little more life out of these components but not that much more that the risk of breakdown was worth it. Mark