Hello All, just did the archive search and did not find relevant info.
My 1995 C280 with the M104 6 cylinder engine has developed a mild noise, apparently after the engine is warmed up.

Using a stethoscope, I was able to pin point the sound as coming from the driver side body of the water pump.
(last replaced Dec 2011 or about 8K miles ago)

The sound is similar to a metal object bouncing around inside the pump.

I can't tell whether the sound is resonating from some other internal engine area but so far it seems isolated to the water pump body.

Is this the sound of the pump bearing going bad?
Can it be something inside the engine behind the pump? Like what?

No water leaks (yet) and no over heating.

When cool, or cold, there is no noise.
Noise is muted and not sharp but audible inside the cabin driver side at idle when engine is hot.(not a sharp noise like a diesel engine 'nailing' noise)

Any tips from C280 owners or knowledgeable Mercedes savvy members?

Thanks !!

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

I'd suggest the first thing might be to remove the fan belt and run the engine for a short time to see if the noise disappears. There are a lot of things close by the water pump that could "phone" noise into it. Of course, don't run it more than a few seconds without the water pump turning. Likely suspects: belt tensioner or a pulley. while the belt is off, try spinning the pump by hand to listen for any noise, and wiggle the pulley to check for bearing play.

DG

Plus two to the guru's suggestion of removing the belt. That will let you know if it's internal to the engine or confirm that it's one of the rotating accessories.

Something in the AC compressor can make exactly the noise you're describing and it travels quite well. That said, if the noise you are hearing through the mechanic's steth can ONLY be heard when it's on the WP and not anywhere else, it's a good bet it is the WP.

Have you slipped off the belt and just checked the WP? Spin it by hand, back and forth, and check for free play, see if it feels/sounds odd.

Good luck.

Thanks Guru and Know, I just retested and let it idle about 5 minutes and then took a short ride. Fans went on and off.
No noise, at idle or after the short drive, then idle.

Actually it seems to be operating cooler now. Just a tad above 80 rather than much higher (95) which has been the norm for years (even after new thermostat).

Weird. Maybe a fluke now that I am scrutinizing. (artifact observation)

I will monitor and if needed, will try removing the belt.

Unfortunately, in another thread, my 300SE's fan is hitting some lower pulley.

For sure I need to remove the belt and test the pulleys for wobble motion.

I will update.

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

The operating temp is probably the same as before. I think the illusion is based on my increased scrutiny.
It normally operates around 95 degrees.

Again I tested it from cold start. No noise whatsoever for quite a long period while 'cool'.

Once it gets to operating temps, that subdued noise is apparent from the water pump body.

Correcting my own previous observation, the noise at issue is not a clear metallic sound but more like a subdued or muted sound 'as-if a hardish object is rolling around in there'.

I am now hoping that it merely is the sound of hot coolant gushing around, although I have never noticed such 'noise' before.

Anyway, I plan on monitoring and will update. No seeping coolant on garage floor.

That is good !

Thanks for everybody's help.

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD