'87 SDL has a high pitch whistle under load... - PeachParts Mercedes-Benz Forum

MercFan · #1 12-29-2012, 12:56 PM

My SDL has a high pitch squeel or a whistle when the boost goes high (starting at around 2500 rpms or so, depending on the grade).

Took it to have emissions test yesterday and the tech thought that it was coming from under the intake manifold but it's hard to locate the exact spot. I've tightened one of the bolts that I found loose and the noise diminished some but it's still singing (just not as loud).

I have replaced the intake gasket when I took off the manifold some time ago. Is there any compound that one needs to apply when re-installing the gasket?! The gasket was German-made (Viktor Reintz) purchased here.

Has anyone experienced that kind of condition and do you have any suggestions on how to narrow down the search!?

LoosBenz · #2 12-29-2012, 01:57 PM

When this happened on mine, it was loose bolts on the crossover. I do not use gasket compound when replacing intake gaskets, nor do I think it is needed. It sounds like you still have a loose fastener (or fasteners) somewhere.

MercFan · #3 12-29-2012, 02:15 PM

Quote:

Originally Posted by LoosBenz

When this happened on mine, it was loose bolts on the crossover. I do not use gasket compound when replacing intake gaskets, nor do I think it is needed. It sounds like you still have a loose fastener (or fasteners) somewhere.

My crossover doesn't have 'perfect' alignment with the intake - there is less then 1/4 difference - could the mis-alignment on there somehow cause the whistle?! I've replaced the gasket on cross-over at the same time I replaced the intake gasket.

engatwork · #4 12-29-2012, 03:21 PM

You are not supposed to hear it. There is a leak somewhere.

MercFan · #5 12-29-2012, 06:01 PM

I've taken my time today and tightened all of the hex bolts on the intake again - and yes, some of them were indeed loose - the access to some of them is difficult.. Went for a ride, the noise is still there but it's whole 2 tones lower than before - noticable improvement but it's not yet gone. All the hex bolts around the intake are now snug...

do I go around once again and tighten it even more?! Don't wanna overtighten - it's aluminum...

engatwork · #6 12-29-2012, 06:10 PM

With the car running spray some wd40 or something similar around the connections of the intake hose. When the engine speed changes you have found where it is leaking.

Mojoan · #7 12-30-2012, 07:46 AM

Most likely he is talking about the intake manifold; try spraying it around the hex bolts, maybe the manifold is warped?

If it does change when you spray it on the seal between the head and manifold, you should try cleaning the manifold and the head really well first and see if it helps.

Silber Adler · #8 12-30-2012, 11:20 AM

It is possible that your loose bolts and pressure caused the gasket to deform and now not offer a seal.

I had a similar noise on my VW after I installed a boost gauge. Turned out to be a leak in the tube I had installed. You might check any tubes that come off the intake manifold.

babymog · #9 01-01-2013, 01:39 PM

I can hear my turbo from around 8psi up. it changes with turbo speed, I know that it is the turbine, but in my case it is the intake tube resonating (not stock intake). On the stock turbo you can hear it if you power it up in a garage where the sound reflects back, again it is through the intake albeit more muffled through the tubing and AFM.

Check your intake path, you might be hearing the turbo if it sounds like a turbine whine. Otherwise look around the pressure-side tubing connections, there should be a slight oil misting around any leaking joints after being driven this way for a while.

oldsinner111 · #10 01-01-2013, 01:43 PM

I love turbo whine

MercFan · #11 01-05-2013, 02:27 PM

I pulled the intake manifold this morning and inspected it - there are at least three cylinder intake holes with more noticeable oil mist spray around them than the rest.

Also noticed something I didn't think about before when I re-installed the intake originally: the glow plug wire harness that runs along the head on the DS has two metal tabs that secure it to the block. During prior re-assembly, I've placed these tabs UNDER the intake manifold, instead of placing them on top of the manifold before inserting the screws. Essentially, what this does is it prevents the intake manifold from tightly fitting against the cylinder head. It's tight enough to work fine under light throttle, but under load, when the turbo is really spooling up the whistle of air escaping through the tiny gap gets really loud.

The noise can easily be mistaken for a slipping belt against a pulley - in fact, I was convinced that was it and even replaced my belt - still the problem persisted.

So lesson learned: be careful when re-assembling the intake manifold - the slack on the glowplug harness is minimal and it's a stretch to get it over the manifold but make no mistake - it must fit over, not under it...

Figured, it's a small contribution to the community.

Thx,
James

MBZ123 · #12 03-20-2013, 07:45 AM

? for OP. Been some time since you stated this was fixed and was looking for further confirmation. Has your fix kept this noise from recurring?

I'm having an issue that I would say is similar to yours where I get a high pitch whistle on my '86 SDL. This is most extreme after car has been at operating temp with continuous driving for about 20-30min. Make no mistake, this sound is LOUD!!! Definitely an attention getter, not my style at all. At highway speed it is audible with any conversation in the cabin almost like it was in the conversation (same level.) Through the city, though, ha, it is the ONLY thing being heard. Definitely a partial load occurrence, as under 2=2500 rpm and over about 4k rpm it fades away.

After reading your thread, did a check for the misplaced tabs and those were correctly situated and the intake appeared properly installed. I confirmed this with the starting fluid test at all charged air connections and down entire interface b/w mani/head. Not the slightest bit of revving.

I'm beginning to suspect the ARV, just haven't found anything solid in the forums yet and seeking info on removing this from circuit to test. Curious to know if your issue has/has not returned.

So back to breaking rock I go.

MBZ123

vstech · #13 03-20-2013, 11:53 AM

I would seriously inspect your fan clutch.

Quote:

Originally Posted by MBZ123

? for OP. Been some time since you stated this was fixed and was looking for further confirmation. Has your fix kept this noise from recurring?

I'm having an issue that I would say is similar to yours where I get a high pitch whistle on my '86 SDL. This is most extreme after car has been at operating temp with continuous driving for about 20-30min. Make no mistake, this sound is LOUD!!! Definitely an attention getter, not my style at all. At highway speed it is audible with any conversation in the cabin almost like it was in the conversation (same level.) Through the city, though, ha, it is the ONLY thing being heard. Definitely a partial load occurrence, as under 2=2500 rpm and over about 4k rpm it fades away.

After reading your thread, did a check for the misplaced tabs and those were correctly situated and the intake appeared properly installed. I confirmed this with the starting fluid test at all charged air connections and down entire interface b/w mani/head. Not the slightest bit of revving.

I'm beginning to suspect the ARV, just haven't found anything solid in the forums yet and seeking info on removing this from circuit to test. Curious to know if your issue has/has not returned.

So back to breaking rock I go.

MBZ123