Growing a Helicopter under my hood - PeachParts Mercedes-Benz Forum

brilliantblue · #1 08-12-2007, 11:03 AM

Hey there, thanks for your time.
I've got a 1984 300D (172,000 miles) that has been developing the b-b-b-b-b sound of a helicopter at lower rpms. the sound gets more throaty as rpms increase. I can feel the corresponding vibration lightly through the shifter, which has a bad bushing and sometimes will rattle in sympathy.

No smoke. virtually no oil leakage or consumption. low blow by. adjusted the valves last week. good power overall.

Please let me know what you think may cause such a sound as I'd like to take care of it before it gets too bad.

Thanks again,
Jeff

Biodiesel300TD · #2 08-12-2007, 11:14 AM

I had a similar sound when I put a straight hose in place of the cigar hose. Which is the return hose from the top of the spin on fuel filter to the steel fuel line. There is a lot of debate on wether that hose it really necessary or not. A straigh hose in its place won't hurt anything, but it can make a little extra noise, but not always.

I experience a plusing noise in my wagon when it had a straight hose, but nothing changed in my 240 when I switched from straight hose to cigar hose.

brilliantblue · #3 08-12-2007, 02:47 PM

thats interesting about the cigar hose. when i need to replace it i'll stick with the cigar rather than switch to a straight one. though i wonder what makes the straight one louder.

i was concerned that maybe i had an injector that wasn't spraying as well. dieselpurge by lubromoly did little to help. i just thought maybe someone out there might have experienced this symptom before and could share an experience to give me ideas.

oldnavy · #4 08-12-2007, 06:33 PM

I had a clutch fan on a 77 V8 Ford that made a noise some what like you discribed when it went bad about 6 months after I bought that hunk of junk new.

TMAllison · #5 08-12-2007, 08:17 PM

Mounts (motor or trans) or flex disks?

d.delano · #6 08-12-2007, 09:11 PM

Check to see if it's the exhaust manifold.

vstech · #7 08-13-2007, 09:48 AM

The way you describe it, I get the idea of exhaust sounds... I second the request for checking the manifold, or the flex pipe after the turbo... plenty of places for noise under there...

tangofox007 · #8 08-13-2007, 10:06 AM

Quote:

Originally Posted by Biodiesel300TD

I had a similar sound when I put a straight hose in place of the cigar hose. Which is the return hose from the top of the spin on fuel filter to the steel fuel line. There is a lot of debate on wether that hose it really necessary or not.

Try driving a couple of blocks without the return hose and draw your own conclusions about whether or not it is necessary!!!

vstech · #9 08-13-2007, 10:09 AM

oh come on tango... most anybody could tell from his text, that he means weather or not it's necessary to replace the cigar with a cigar vs straight hose... not without it altogether...

Stevo · #10 08-13-2007, 12:52 PM

Quote:

Originally Posted by vstech

oh come on tango... most anybody could tell from his text, that he means weather or not it's necessary to replace the cigar with a cigar vs straight hose... not without it altogether...

I took that to mean..take the hose off to see if the noise stops, not weather or not the hose is needed.

oldnavy · #11 08-13-2007, 12:59 PM

Quote:

Originally Posted by Stevo

I took that to mean..take the hose off to see if the noise stops, not weather or not the hose is needed.

I sure didn't, and I am an easly confused old fart.

I mean when you stop and think about it you have to remember that fuel comes out that return hose and he knows that I am sure. If not he doesn't need to be under the hood.

Stevo · #12 08-13-2007, 03:50 PM

Quote:

Originally Posted by oldnavy

I sure didn't, and I am an easly confused old fart.

I mean when you stop and think about it you have to remember that fuel comes out that return hose and he knows that I am sure. If not he doesn't need to be under the hood.

I would think the word "return" would pretty much make that a "no brainer"

oldnavy · #13 08-13-2007, 04:10 PM

Well I took it to mean was the cigar hose needed or could regular hose work. And I remember those discusions a couple of years ago on here about if it was needed and why it was suppose to be there. Something about lessening a return pulse back through the system.

VegiBenz · #14 08-13-2007, 06:33 PM

I'll second (or third) the cigar hose. My old 300D and my current SD both have made the noise and it was because of the straight hose in place of a cigar hose. It somehow dampens the pulsations of the return line which does bang around and make a pretty good raquet. A straight hose will work for sure but won't dampen the pulsations that are there. Maybe the pulsations get worse as the straight hose "seasons" and gets worn in over time? Try a new cigar hose, you will probably be pleased.

brilliantblue · #15 08-14-2007, 02:12 PM

thanks for the advice. i will check out the exhaust and mounts/flex disc. i,ve got another exhaust from a parts car so i'll "hope" thats the source. this car has the cigar hose, which appears flawless, so i don't think i'll replace it. i was concerned that the noise could be from a failing injector.