New water pump making whirring/roaring when cold - M103 '88 300SEL
 

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?

Question
 

How old is the tensioner and the belt?

86560SEL, it may be a failing fan bearing bracket that is making the noise. I had that experience after a mechanic replaced the water pump in our 1991 300CE, due to the drive belt being over-tightened. If you are not a DIY'er replacing the fan bearing bracket requires stripping down the front of the engine ... quite expensive if you're paying a mechanic. If that's the problem buy a reconditioned fan bearing bracket from a MB dealer, rather than some cheap knock-off brand.

I would take the car back to the mechanic and get an explanation for the noise. There are many things that could be making the noise. In any case you would expect the noise existed when the mechanic finished replacing the water pump, and didn't suddenly appear right after you got your car back.

Not sure about the tensioner, but the belt is brand new.

Yeah, it didn't make a peep before that. We had the pump replaced because it was leaking water. We have already spent over $400 in getting the water pump replaced.

We will see. Thanks!

This is one of the reasons why I didn't install customer parts when I had a shop. The last person to touch the car is held liable for anything that fails later, even if they did nothing wrong.

Does this have an automatic or manual tensioner? A bearing starting to fail can be made louder my adding tension.

At this point we don't know what is making noise and can't reliably diagnose remotely.

My mechanic is going to look at it on Wednesday. He has a garage behind his house and he will sometimes get the parts, or he will let the customers bring them, as they are normally parts he would get anyway. I spoke to him about it at length and he said this car has an automatic tensioner and he did say that with the new belt installation that he added tension to it, but he said a little more, not much. It could be that, but it sounds to me like it is the pulley above the alternator, but I could be wrong.

Thanks.

an 88 103 engine has a manually-set tensioner. there's a screw, a nut, a guide and a pointer. not automatic. good luck, chuck.

86560SEL, as far as I know the tensioner on your vintage engine requires a manual adjustment, as porkface states. If somehow there is an automatic tensioner on your engine I am not sure how your mechanic could possibly add tension. That doesn't make any sense. Does your mechanic work exclusively on MB and BMW vehicles, or does he work on any brand vehicle?

When adjusting the manual tensioner it's necessary to loosen the center bolt on the tensioner 1/2 turn or so; otherwise, you will destroy the tensioner when turning the adjustment rod. If your mechanic was unaware of that step, he likely destroyed the tensioner and you will need a new one.

How strange. My mechanic said it had an automatic tensioner. He just had it apart 4 days ago. Oh well.

He usually works on all makes and models, but works on a lot of Mercedes and BMW's. He brought up the conversation to me when I was talking to him about the noise, he said your (my) car has an unusually seen set up with an automatic tensioner... he could be wrong though. I have no idea. Lord knows I know nothing about them. Well I hope he has no destroyed anything, especially if it requires tearing down the front of the engine again. I hope just once it is nothing too serious. Have not been able to catch a break here lately. We are already over $400 in a new water pump... I hate to spend another $400.

Thanks.