Starter? Alternator? or Battery?
 

Hi all,

Had what I thought was a bad starter in my wife`s 190e. Was cranking slow and slower for a few weeks and finally bit the dust in a Target parking lot. Battery appeared strong.

Got a replacement McParts starter and installed it. First cranks sounded great... subsequent cranks sound terrible and ultimately result in the starter not making full contact with the ring gear. Ouch!.

Put a charge on the battery and the car starts strong first few cranks and then again starts to fade.

Battery is about 2 years old. It is a GOOD Interstate monster that put out close to 13.6v sitting (wow) even after it abusing it with the starter. Checking the charge from the alternator and I am reading about 13.8v at idle and with most accessories running.

Is it possbile for the alternator to put out enough voltage but not enough amperage to keep the battery properly charged?

Course of action?

Curious.

Tinker

I think your problem lies in the McParts starter. Double check the water level in your battery, voltages sound OK, but check the level. Haven't heard much good about anything less than a Bosch or MB reman starter.

In my opinion its best to have the starting and charging system checked out the proper way. A VAT 40 or eqivalent tester will tell you a lot about your problem.Start off with a fully charged battery..load test it for 15 seconds,record your readings,disable the vehicle so it wont start but will still crank..check your starter draw,record your readings,now enable the vehicle for starting and start it...run it up to 2000 to 2200 rpm and load the system to get your alternator output,record your readings.I think that somewhere in the test you will find your problem..should save you a lot of money in changing parts the hit/miss method.If you have no VAT 40 or equivalent then any good automotive repair facility will have one on hand.
Hope that this helps
Phillip
1992 300Ce
84,900 miles

Tinker,

Check the connections to the battery and the starter. The battery ground, and the cable connection from the line to the positive post from the starter can be getting corroded. Poor connections usually get much hotter than the cable itself as there is a significant voltage drop across the corrosion products. If the cable itself is getting very hot there is a chance the cable has suffered some damage from either heat or being crimped during some other repair effort.

Anyway, the idea that the starter is getting weaker as it runs longer sounds like you have a connection problem, cable problem or the starter insulation is bad. I have seen the starter issue on Diesels regularly. If it is the starter, buy on from FastLane as theirs are Bosch rebuilds and get the stator rewound if the insulation is weak. Most other starter rebuilds are confined to mainly mechanical items, like bearings, brushes, the solenoid or a paint job. Rewinding cost effectively requires special tools and machines typically only available at the OEM.

Old stuff, especially starters that have had some hours spent cranking cars reluctant to start will have problems with the winding insulation. This is because the starter output rating is based on being used "intermittently" meaning for 10 seconds or so a couple times a day with long cooling down periods between starting attempts. If you run the starter for a few minutes continuously you will overload it as its continuous rating is much less than the intermittent duty rating. It will heat it up significantly more in continuous duty, which is not a design condition. Thus, the insulation will break down, leading to lower output and internal leakage of current (shorting), and ultimately to the demise of the starter. Fixing bearings and solenoid won't address the winding problems.

Good luck! Hope this helps, Jim

Thanks for the input guys. I am kicking myself for not getting a rebuilt starter from the dealer. Wife needed the car the next day and I was desperate and went to McParts with its `lifetime` warranty. The thing is, it`s not the first starter I got from them. The first one sounded worse and also grinded on the ring gear so I swapped (not a fun job) it out with this latest one. This one has the same symptoms, but only with continuous cranking. They were/are both Bosch starters but as you guys have indicated there are degrees to their rebuilding. Maybe this was a $175 lesson I needed to learn.

I will get the battery load tested and double check the cables to be safe. The battery took a bit of abuse in the previous weeks trying to diagnois a vacuum leak/fuel problem. I put a charge on it last night and it initially takes only 3 amps and drops pretty quickly to an amp.

Thanks

Tinker

Tinker,
I go once the same problem with a French car.
The cure was simple. I drove to a good batteryshop
to replace it by a new one. The shopowner refused!
He said " Let's first check out the old one!"
And right he was. The old battery withstood a regular
15 sec. test but after a hole minut under full load, the
capacity dropped spectacularely.
So we put in a new one and all problems solved.
At several occasions he did tests for me on other
batteries and I had never to pay for it even when
I was not buying anything!