Water Pump Noise?? Please help!!
 

Hello folks,

I've got a problem that's been nagging me for a few months. When I start my car cold, I hear a whirrring rattle from the engine (M119.960 V8 from 1992 500SL). As the car heats up after driving for 15-20 minutes, the noise is more subdued but it is definately still there. This is very consistent and happens everyday.

Finally, yesterday, I removed the serpentine belt from the engine and then started the car. The noise was COMPLETELY gone. :-) I was feeling pretty good knowing that it DEFINATELY is a drivebelt driven accessory but which one??!? I tried listening with a stethoscope to no avail. I tried turning all the pulleys with the belt removed but they all seemed fine. Now add this to the pot, in the last 6 months (and roughly 14,000 miles ago), I've replaced:

power steering pump
alternator
smog pump
a/c compressor
belt tensioner

Therefore, that leaves....the water pump.

Now, when I put the belt back on the car and retension it. I can feel an EVER SO SLIGHT, and I mean to stress the word SLIGHT play in the water pump pulley. My question is this:

My water pump currently doesn't leak, the engine temperatures remain steady, however, it has never been replaced on the car. Also, the fact that the noise gets less when the engine heats up seems more consistent with the water pump (hotter coolant expands tolerances, etc.). Can a bad bearing throw off the position of the plastic impeller perhaps causing the noise? Once again, it sounds kinda like if you spun a wheel on a bicycle and inserted a playing card into the spokes.

I'm tempted to pull the pump and replace it with a new MB one.

Also, I've checked all fluid levels (power steering, hydraulic fluid, etc.)

Thanks and sorry for the long message!

Satish
1989 560SEC - with M119.960 V8 32-valve transplant
1999 E430 Sport

Sounds like you are pretty handy with repairs, I say go ahead and change the pump, it can't cost very much.

You might be hearing the pumps vanes hitting the housing inside. That could account for the sound.

Thanks Ed,

I too suspect that it's the pumps vanes hitting the block. The pump is $234 from the dealer for an MB one. I made some calls and some aftermarket ones are in the $150 price range. I'll also change the thermostat I guess and replenish with fluid.

Satish

I had a water pump on my 420 that was extremely sloppy and worn out. But it did not leak a drop of fluid. It made a horible noise but never leaked. Us a stethoscope and you would be surprised what noises you can locate.

Hi Dave,

I used a stethoscope but couldn't locate the noise. What did your sound like on the 420?

Satish

Two things.

First, I have seen water pumps and the front main seal make noise. In the case of the front main, I pull back the lip and applied some oil. Case solved.

If you want a good pump, we sell them in FastLane and will deliver to your door.

Thanks Donnie! Tell me about the noise that the water pump makes. Mine is much more subdued as the car reaches full operating temperature (but is still apparant). This leads me to be highly suspicious of the water pump. It sounds like someone holding a plastic playing card in the spokes on a bicycle wheel that is spinning.

Also, how much is the water pump and thermostat? It is for the M119.960 1992 500SL engine. I'm thinking about doing the timing chain on this motor at some point in the near future. Perhaps this may be the time since all that MAY have to come off?

Thanks

Satish

It made a nasty growly noise. There was siginificant slop in the shaft. It was way past its prime. But it never leaked. First one in my experience that bad and did not leak. Using the scope there was no question as to what it was.

Hi Dave

My Alfa GTV6 had a huge amount of play in the shaft and the impeller was whirring like the playing card scenario. There was some evidence of metal in the coolant, and it generally sounded like a doomed engine!
Yup, didn't leak a drop!

Did the water pump have play in the shaft that you noticed AFTER you pulled out the old pump? I cannot notice much play at all in the pulley.

I took it to the dealer and they replaced the tandem pump (self-leveling/power steering pump) and belt tensioner all under warranty but it didn't change a thing.

The A/C compressor, alternator, and smog pump are only 6 months old. Also, why would the noise be more subdued once the engine is fully warmed up? Makes me think more and more that it IS the water pump. BTW, this is the original water pump from this engine (1992 M119.960 engine).

Satish

With the pump in place and tension on the pulley it is very difficult to observe any play. Play does not mean anything at all. I have seen pumps that have no play, dont leak but make an incredible amount of noise. It just depends on where they are in their death cycle. I recommend that you use a stethoscope and listen to each of the rotating components bearings and it should be very obvious which one is the problem.

Hey Dave - You are right on the money. If someone has not used a stethoscope and finally breaks down and buys one - He will kick himself for not having done it before. It is amazing the sounds you can pick up and pinpoint - and very quickly too. A real must in all tool boxes!
Maurice

Dave, as a retired electronic tech, I am curious. There must be a cute story behind your signature "electrons can do anything". What is it????
Maurice

Thanks Dave,

I took a long phillips screwdriver and placed one end on the pump and my ear against the other end. Sure enough, the pump is bad. I ordered an original MB waterpump, gasket kit, thermostat, and MB coolant today. I'll attack the job on Tuesday.

Thanks again everyone!!! I'll post my results soon.

Satish