MY99 E300 hot start whistle, what is it? - PeachParts Mercedes-Benz Forum

jnc19610 · #1 07-13-2006, 02:23 PM

My 99 E300 has a very odd whistle when it starts hot, that I can't quite diagnose. It didn't make the noise over the winter. It doesn't ever make the noise on a cold start. Only on a hot start, after it has stopped for a few minutes. If I start it right away, after stopping, it doesn't make the noise. If I let it sit for say, 1/2 hour, it doesn't make the noise. It only makes the noise if hot, restarted after a 5 minute or so heat soak.

I think it's vacumn related, but I can't find it. If I put the hood up, start the car, and quick run to the front, the noise is already gone before I get there. It almost seems like it comes from behind the dash, but I can't really tell.

My other guesses were the electric fans starting, or a vacumn leak under the dash, or maybe an idler on the serpentine belt. It is really weird, cause it whires and whines for about 3 seconds, then stops. If I quick stop and restart, no noise. If I wait 5 minutes and restart, there might be no noise, if it isn't hot enough.

Bottom line is, I'd like to know what is it. Otherwise, it's a fine running machine, getting 29mpg on the highway, smooth as silk.

husk · #2 07-13-2006, 02:57 PM

mine does the same thing, not sure what it is

rrgrassi · #3 07-13-2006, 03:54 PM

The starter bendix may not be retracting fully, and is being spun by the flywheel for a moment. Since it goes away so fast, it wil be hard to tell. The belts can chirp like that also, if they are a little loose, or glazed and cracked.

jnc19610 · #4 07-13-2006, 09:00 PM

I don't think it's a starter. It could be a belt, but I would think that a belt noise would repeat on startup. This noise doesn't repeat, if you shut down, and restart immediatly. Wait 5 minutes for a little heat soak, or vacumn leakdown, and it does re-occur. Wait 10 minutes, when it's a wee bit cooled off, and it doesn't happen. I'd think a starter noise or belt noise would repeat, without the wait.

husk · #5 07-25-2006, 01:48 PM

Mine does exactly the same thing at the same time intervals, if you ever find out what it is let me know. I think its related to the A/C

F18 · #6 07-25-2006, 02:38 PM

Quote:

Originally Posted by husk

Mine does exactly the same thing at the same time intervals, if you ever find out what it is let me know. I think its related to the A/C

Thats a good question.....is your A/C ON when you start? The extra drag from the compressor might be making the hot belt chirp. You said it made no noise this past winter.....The A/C would not have engaged or you would be running in the EC mode on your environmental controls. Try a hot start with the EC botton ON which will shut off the compressor.
Good Luck finding the problem
Cheers

husk · #7 07-26-2006, 01:19 PM

Quote:

Originally Posted by F18

Thats a good question.....is your A/C ON when you start? The extra drag from the compressor might be making the hot belt chirp. You said it made no noise this past winter.....The A/C would not have engaged or you would be running in the EC mode on your environmental controls. Try a hot start with the EC botton ON which will shut off the compressor.
Good Luck finding the problem
Cheers

When the AC is on it will always do it, when the ac is off it will sometimes do it.

F18 · #8 07-26-2006, 02:23 PM

Quote:

Originally Posted by husk

When the AC is on it will always do it, when the ac is off it will sometimes do it.

It seems like it is associated with the A/C compressor clutch plate or the belt and A/C compressor pulley.

With the engine off inspect the a/c electromagnetic clutch plate in front of the A/C compressor pulley. With every thing off it should spin with your fingers without any rubbing. Sometimes rust scale or dirt will jamb in the narrow clearance between the clutch plate and the compressor pulley and make all kinds of wierd high pitched noises. Use a small brush (tooth brush or small wire brush) to nock the crud lose around the rim edge. Drip a little WD-40 in between the A/C clutch plate and the pulley (careful...you don't wont it on the belt). Also buy some spray on "belt dressing"..its inexpensive, and condition the belt, it may be worn and glazed which may cause it to slip when its hot and the A/C compressor is engaged.. Try it...it won't hurt and if it cures the problem then you got away cheap!
Thats all I can think of.....may be someone else can shed some different light on the problem if it does'nt work.
Cheers,

Rick Miley · #9 07-26-2006, 03:18 PM

Yes, mine will do that on occasion as well. It's a very difficult noise to describe, but I would swear it is made by a vacuum and not anything mechanical. At any rate, mine has been doing it for several years and still runs fine, so I don't worry about it.

F18 · #10 07-26-2006, 04:35 PM

Here is another fleeting thought.....check to see if there is a loose clamp or leak in the intercooler hoses. The two 2" hoses are to the bottom right of the engine and radiator ....you will need to remove the front chassis splash guard to get a good look at them.

My 98 E-300TD is the same set up as your 99. I put in a new radiator once and forgot to tighten a clamp on one of the intercooler hoses and got a slight hissing or whizzing sound. I found the leak and tightened the clamp and the sound was gone.....How that would relate to it happening in yours when its hot....I don't know! May be when the air leaving the turbo is hot the hoses soften and leak more...?

husk · #11 07-26-2006, 09:45 PM

I just got my car back after my mechanic installed a new suspension and did not notice any clamps etc loose. I had him check it and he said it could be the oil pump, or the A/C Compressor pulley.

On an interesting note I noticed a silver pipe underneath the intake manifold (it has a sensor and wire) is leaking some sort of oil from the connector. Not sure what this pipe goes to or why its leaking oil.