Belt Question
 

I recently replace all the belts on my car. I looked in the MB manual and they give a tension setting for new and for used belts. I always readjust belts after a little time in use but at what point are the belts considered used. Every other car I have ever had I just made sure the belts were tight but I went out and bought the clicker type tension tester recommended by MB for this project.

Some publications say that one trip around the pulleys is all it takes for a new belt to become an old belt.

That makes sense in that it is the flexing of the material that causes it to stretch etc. The manual say to tension some of the belts to 50lb new and. I think, 30lb used. I have been running them for 3 weeks so I guess I'll go with the used setting.

That should be a very safe bet. I theory, the belts would have "slackened" to the used belt tension as they broke in.

I suspect that the new belt working deeper into the "V" of the pulleys accounts for more tension loss than stretching.