w126 300SD squealing while accellerating at any speed
 

Hello All...

interesting issue with my 1985 300SD: Squealing noise (almost seems boost-related) while accelerating. The turbo has almost no lateral play to speak of and boost builds rapidly; as it should to factory spec of 0.8bar. This squealing noise seems louder when the engine is not at full-operating-temperature in the morning but maybe it's just my ears/mind fooling me. Oil change with Amsoil, etc and checking for oil leaks around turbo/oil lines = no difference. I noticed the noise this evening while driving with the roof and windows open even at full-operating-temp and decided it was time to ask :singer: the experts! Anyone heard,seen, or experienced this issue? I've quickly inspected the turbo for shaft-play (as stated earlier), and given the intake gaskets, etc a once-over but haven't found anything which looks to be the cause just yet. I'd like to get this corrected before it gets any worse or causes damage which requires major down-time.:(

Any pointers will be sincerely appreciated! :nice:

Did you check your belts? AN alternator belt loose can do this. Also check for loose or missing ehxaust manafold bolts.

I second the Alternator belt check. I had the same issue and found that one of the two belts had stretched. Replaced them both and the noise went away.

yup. alternator belt... and don't figure it's ok, just because it's tight. it has to be in good shape too. get a MATCHED pair of new belts in there.

you said it may be boost related so it might be the ARV.

The best way to check this is to have someone (you trust ;) ) put it in drive and apply the brakes and accelerator while you search for the squeal under the hood.

Add w/e-brake applied also...not pointed towards the house or other objects.

YOu have an 85... it IS the ARV. I know everyone will tell you belts, but I bet it's the ARV since it sounds like you noticed it was boost related. ARV= Air Recirculation Valve... its an emmisions only devise to allow a large enough flow through the EGR during certain boost levels... it HOLDS BACK boost and limits power when it's open... I took it apart when I had the turbo off and plugged it permantly, but the plug will do it.

See that blue line going into the side of the turbocharger compressor?? Pull it off and put a BB into the rubber connector and smile as the squeeling goes away.

thanks for all the replies!
 

forgot to add the fact that all belts are brand new and properly tensioned... I already (accidentally) have BB's in the EGR and ARV lines :D....(for safety reasons, of course!) Maybe one of the lines is split or cracked. Will check it this evening. Thank you all very much for the input! Now if I could just get the cruise to work at speeds over 70MPH... (please see my other posting, if anyone has a clue as to the cause of this after trying 3 different reman. amps :confused:...)

thanks again!
Erik d.

no hoses/tubing found loose or damaged. Belts all secure. Still squealing.... :(