Hello all,

I have 139K on my E300DT. I purchased it 4 months ago.

The engine always made a air rushing noise when I accelerated and I thought that was normal. Recently there has been a whining noise coming from the engine bay. The noise is rpm dependent and is happening whether the car is in Park or Drive, moving or not moving... The noise did not increase or decrease when I turned the steering wheel or when I engaged the A/C.

I took out the serpentine belt and started the car (for 20 seconds or so) and sure enough the noise is gone.

I am thinking that I should replace the belt pulley as the culprit. I did some research and it looks like I have to take the fan clutch off to get better access to the pulley bolt.

Since I will be removing the clutch, is there a way to determine if it is bad? Should I just replace it, assuming that at 139K it might go bad sooner than later? Can the clutch make a whining noise?

Since I am so deep should I consider replacing the water pump? I am assuming that it won't require much more work to get at the water pump. I could not find a DYI writeup on changing the water pump. Again should I just replace it, assuming that at 139K it might go bad sooner than later? (not knowing if it was ever replaced).

Any ideas or suggestions are greatly appreciated.

Thank you.

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1998 E300 Turbodiesel 184K

With the belt off you should be able to spin each pulley and see if any seems to have strange resistance. That's probably the one causing the noise. If it is just the idler pulley I wouldn't even consider doing anything more than that as "preventive maintenance". My water pump is original with 157K miles on it and is still fine...why fix it if it ain't broke?

The air rushing noise could be caused by a leak in the connection where the charge pipe connects to the intake manifold or elsewhere on that pipe. That's basically the pressurized air from the turbocharger in that pipe. There is a large o-ring at the end of that pipe that often gets overlooked for replacement when the intake is removed. It may just be leaking enough to cause your noise.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Easy to determine if the fan clutch needs replacing, when up to temperature stick a carrot in the fan blades. Chopped carrot = clutch ok. Whole carrot = clutch faulty. Also, turn the engine off and if the fan keeps spinning then replace the clutch.

I wouldn't bother with the water pump.

My experience in the last 4 months of ownership (first MB) is that there is a lot of poor engineering in this car. I've already had 3 separate issues (including the current one). That is why I was thinking of replacing the parts that I will be removing anyway. Don't get me wrong, I also don't want to spend money like I've been doing in this car the last few months.

Example of poor engineering:
The fan regulator died. This is a common item to break in this car, but what makes me mad is that if I wanted to purchase a new one, I would have to replace the motor as well. The new fan, which was re-designed does not fit on my current motor. Hopefully the new regulator is better engineered. I didn't buy the new regulator for my car, instead I purchased it for another model and spliced the longer wires from my old regulator.

I think another example is the oil pump in the 1998 model was re-designed for the 1999 model. I saw some posts about this issue.

I can go on but that is not my purpose here. I really like driving this car, I just don't know if I like being the owner.

If I don't hear otherwise, I probably won't do anything to the water pump. My last diesel VW Passat "required" a new water pump with every timing belt change.

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1998 E300 Turbodiesel 184K

Yes, well, now that the car is nearing 10 years old it will have some issues, sure. The reason your VW "required" a water pump replacement is not that it was really required it is just that you do 95% of the work needed to replace the water pump in changing the timing belt, so for the extra cost of the part which is minimal compared to the labor it is highly recommended that it be done as part of the job as PM. This isn't the case with the OM606.

I haven't heard of any issues with the oil pumps in the '98. What I can tell you is the entire fuel system is an issue...o-rings can and will leak. They are not expensive nor difficult to replace but are just a headache which, if you own the car for any length of time you will undoubtedly deal with. Also, if you are very lucky you will not experience a broken glow plug stuck in the cylinder head, that's another weakness.

Yeah, the blower regulator is a problem part but you found the workaround to replacing the motor so for a small fraction of that cost you have fixed the problem and as you now know it was not all that difficult to do it. Get familiar with the window regulators next...oh, and then there is the K40 relay which can cause the engine to stop running at random times...

It took me 2 years to iron out all of the issues in mine, but for the past year it has been as reliable as any new car I have ever owned and hasn't given me any trouble whatsoever.

The way I look at it is this...if I wanted everything perfect I'd drive a new Lexus. I paid a small fraction of the cost of a new Lexus for my '98...in fact I paid a small fraction of what my car cost in '98. To get something which drives as well which is newer and superior in quality I would have to put at least $20,000 more into it in addition to what I could sell my '98 for. For that $20K I can probably keep my '98 perfect for another 10 years.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

As a follow up I want to say that replacing the pulley idler, shock absorber for the belt tensioner, belt, and the radiator fan clutch did not fix the whining noise.

I incorrectly assumed that the idler pulley was the culprit. When I started the car without the serpentine belt the whining noise was gone.

Now that the new belt and tensioner are on the car, the noise is louder than before. So this must point to something connected to the serpentine belt.

The noise is coming from the area of the alternator (passanger side). But the water pump is also in that area. The turbo is also on that side of the engine.

I am suspicious of the alternator, but I don't want to change parts that might not solve this problem.

Any suggestions?

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1998 E300 Turbodiesel 184K

Mechanics often use a stethoscope or length of vacuum hose stuck in their ear as a "probe" to help them pinpoint the origins of noises, so I would suggest you try this and you ought to be able to tell if it is coming from the alternator or the water pump. Both have bearings which can cause this kind of noise. Good luck.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Check the motor mounts to see if they are partially or wholly collapased.

17mm = New
13mm = Bad

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

Did you spin every pulley with the belt removed as suggested by nhdoc?

I had a similar issue with the bearing in my A/C clutch pulley "shelling out". Was REALLY wobbly with the belt removed.

Since you did effectively tighten the belt with its replacement (new belt is smaller and not streched as an old one) you've increased the preload on whatever pulley is the culprit, so it makes sense that the noise is louder.

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2005 Pathfinder LE
2001 E55
1998 M3
1982 320i

Have you run any cursory checks on the alternator, lights on while starting, voltage output, etc?

Ok, so I think I got it. I had to pull the fan clutch and fan off again, so I could get to the alternator.

Once the belt came off, I pulled the belt off as well, and yanked on the alternator pulley. It was rocking and rolling. So off came the alternator and now I have to look for a new one.

I will probably try to get the one from Auto Zone if I want to fix it right away.
The 115A alternator at Auto Zone is $220 for a rebuilt Duralast. The other sites ********az, buymbparts, etc are all around $360. The Auto Zone alternator does not come with the pulley. Can I expect the others to come with its own pulley?

Thank you.

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1998 E300 Turbodiesel 184K

You might only need the pulley. I believe that yours has a ratchet and bearing in it. Perhaps just these have failed.

The shaft has movement inside the alternator as I pull up and down on it.

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1998 E300 Turbodiesel 184K