How do I adjust the belt tensioner on an OM606
 

Or is it even adjustable? I know it is on the OM603. I think my serp belt might be a little loose, because every once in a while it squeals like a pig when I turn the AC on, and occasionally the AC cuts out when I'm standing still in a way that feels like the AC clutch isn't engaging.
Also my clutch fan is kinda sappy, but got a bit better when I replaced my badly worn old belt.

I don't think it is adjustable on any of OM60x engines. It is automatic belt tension system which is controlled by the spring and the tensioner shock. If the belt is loose then very likely you need a new shock or spring. The shock and the idler pulley rarely last more than 50k miles in my experience (400k miles on the OM602 motors).

Tan

'87 190D 2.5t
'91 300D 2.5t
'87 300TDT

Are you sure the belt is too loose? Possibly the clutch going on the compressor? The belt isn't adjustable on the 606. On mine the spring seemed to last, the shock would only go 30-50K before it started rattling and I replaced the pulley once at about 180K.

Answer
 

Inspect the

Belt Tensioner Lever, At Belt Tensioner Pulley
MB# 606 200 00 73

For proper motion = it can in rare cases seize on the pivot pin #17.





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As for the sappy fan clutch, it's actually NOT sappy that's the problem... :) These clutches tend to leak out the viscous oil and over time lose effectiveness.

My car being a prime example at the time.

I'm wondering if your compressor is on it's last leg?

Ive been chasing around a squeekey belt issue for 2 months now on a 190d ,same similiar problem .Not to hijack thread but we may have the same problem if Im right.Early on I would spray wd on the power steering bearing and the noise would go away ,then reappear ,It seemed to be the problem ,wrong.I then checked the shock and spring ,all was good.Yesterday I bought a new shock just to make sure ,installed it ,no go.I did notice though as I inspected the pivet piece that the shock and spring attach on to was loose ,it rides like a seasaw and looks like a wishbone.This is my next replacement.It seems that if it is loose this bearing is on its way out ,Im suspecting its letting the belt move from what should be true dead on center but maybe letting the belt have a squirreley ride .

Your clutch IS disengaging. I have a 1991 350SDL and it has the same problem. Your clutch will kick out if your tach and your compressor speed are not the same. That KLIMA RELAY, at the firewall mid engine, is there to keep you from throwing a belt in case of compressor lock. So, like me, you have to figure out if its a pulley, tensioner, or belt stretch. I've been chasing my grimlen ever since I replaced the belt which makes me wonder if my belt is a 1/2 inch too long.

most loose belts are caused by glazed out belts and bad tensioner shock. Investing in a clutched pulley on the alternator is also wise - it extends the usable life of the belt tensioner shock.