I have a 1989 300E. It is experiencing electrical failure after extended drives with air conditioning and equipment. I can jump start the car and it runs fine----and slowly discharges. Then try to restart, only to find the the engine will not turn over. Advice given---check the battery and alternator for adequate charge cycle. Also, check the voltage regulator to ensure operation. My question---concerning the prior repair of belt tensioner--a full replacement of $560.00. If the voltage regulator is the problem--did I need the belt tensioner replaced. The serpentine belt was obviously loose---but I wonder now if I was taken advantage of-----Is there a test to determine what specific repair is needed? Thanks for your assistance.

If the belt was loose then the replacement of the belt tensioner was justified. Have you had the altenator output checked? What was the result of this test? It appears that you have a problem with the charging system.

Hi Corky---I have not had the alternator checked yet----What is your opinion regarding this type of problem? I thought the belt could simply be adjusted---like my 300D Turbo when belts were replaced. If it only needed to be adjusted----then I overpaid the service center-----What are your thoughts?

Ammadeus
There is no adjustment persay on your 89 124
chassis car. When the belt is to be replaced the tensioner is releavied and then reset after the belt is reinstalled. The tensioners job is to maintain the tension of the belt. This is accomplished by a rubber type insert inside the tensioner. When this rubber material wears out tension is no longer maintained. If your belt had not been removed in the day or so pryior to this happening there is no other assumption to be made except for the tensioner to have failed.
Professional technicians are not in the business if repacing parts for no reason at all.

I have seen many times that the belt tensioner fails right after being adjusted. This is especially true when the tensioner is old! The rubber will find a spot where it likes to travel and when a new alternator or belt is installed the tensioner fails. It is not the tech's fault when this happens, just an old part!! When I feel it is called for I write one on the estamate sheet to warn the customer in advance!!

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM