We finally had to have a new water pump installed on my mothers 1988 300SEL (M103 engine).

We bought all of the parts and had a mechanic do the labor. I picked the car up, drove it home - the car was already warmed up, I guess from the mechanic running it, checking for leaks. He put on a new water pump, thermostat, belt and drained all of the old coolant and refilled with new Zerex G05 coolant.

Well the car set for a few days, as it isn't not used much. I was going to drive my mother to town and when I was warming it up, I noticed a roaring/whirring noise at certain rpms. We started to leave at it was making a really loud noise, started back home, but then it started to quit. We went on and it never made another sound. I kept a check on the gauge, it was running in the normal range and no leaks.

My question is - is there a break-in period for these? I don't think it should be making any noise. I was also thinking maybe there was air in the cooling system causing it. I don't know.

I am trying to do a little research before calling my mechanic. It was a pretty big job labor-wise and I hate to think it may be a bad NEW water pump and it has to come off again.

Thanks.

No break-in for water pumps; it should be nice and quiet, even if there was some residual air in the system. Could it be the fan clutch? They will tend to howl a bit when first started cold, and then loosen up as the motor warms.
Also might check the tensioner pointer to be sure the belt is properly tight.

DG

guessing here but i'd say the shop set the belt tensioner too tight. good luck, chuck.

Thanks!

Thanks!

I started the car and I do believe the sound is coming from the tensioner (or pulley) located above the alternator on the passenger side - that may just be a pulley and not the tensioner, because I do not see where adjustments can be made there. it looks like the tensioner may be below the water pump? I hope not, it would be terrible to have to remove all of this again. It was a pretty time consuming job. Our mechanic charged $200 labor.

It definitely was not making the noise before the mechanic installed the water pump. The belt does not seem too tight or too loose. Maybe it is a coincidence that the bearings have went out in it at the same time the belt was replaced?

How old is the tensioner and the belt?

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'89 260e (212K Mi.), '92 400e (208K Mi.), '92 400e (not a misprint) (146K Mi.), '95 C220, '81 240D--Sold