Hi All- need some help here. I just purchased a 2013 GLK 350 4Matic with just over 40K miles and a great service record. Warranty is out so looking for expertise and help, not judginess please!

Just recently, I started noticing that at times (usually when it was parked for a few hours or overnight), the vehicle was slow to crank, with very similar symptoms of a bad battery or alternator. Took it to AutoZone and batter checked out fine (looks brand new too). The weird part is that if I try cranking long enough, it eventually starts. Once it's going, zero issues and if I turn it off and on, no issues either until it sits for a prolonged period of time. The situation is getting worse, with this occurring more and more (working on attaching video today or tomorrow). I'm thinking this could might be a failing starter relay or starter (although it seems odd for such low mileage). Has anyone heard of this prior? Any other ideas? Thanks in advance for your help!

Saul

 

Generally speaking failing starters usually will get worse when the car is hot however that's not a rule of course. I do agree with your logic however. I would imagine that part is quite expensive. I would recommend checking all connections for possible corrosion. Maybe you'll get lucky.

 

When you took it to auto zone to test the battery the motor was just shut off and the battery just fully charged , test the battery voltage before you start it, leave the hood open all night , then try leaving a charger on it all night . Is it a mb AGM battery? Is it AGM ? The charge profile is different. You need an AGM battery and portable charger that has the AGM profile. Charging an AGM battery with a non AGM proflle charger and the battery won’t fully charge. I know it’s confusing but figure out what you have first.

 

I sure agree about heat being a factor,. One time a car I owned had a problem with a ground wire going to the starter and did not present that as a problem using a tester. After a few days of being unable to locate the problem, I spent time to track down each wire and finally found the source of the shorted ground wire that was seperated in half and barely attached to the wire plug it went into, All this was after replacing the starter which was within service range of operation but was very old.

 

have you had the fuel pressure checked? " The weird part is that if I try cranking long enough, it eventually starts."

 

Ok - so, as it turns out, despite the positive test results from the AutoZone test and a relatively new state-- the battery turned out to be bad. . Rookie move. Thanks everyone for the help.

I took it to a shop that did a (free) inspection using a Snap-on device and the results showed the battery was failing (contradicting what I heard from AZ). So, just this evening, I replaced the bad Exide battery with an Autocraft AGM battery from Advance Auto and the thing cranks and starts like a dream. Sorry for sounding the alarm for help when the solution was so simple. I had simply assumed the AutoZone test was right. @Mmr1 - can't recall if the engine was on during the test, but you're probably right that the battery was potentially fully charged at that time.

Sharing in case this helps anyone else out there.

Saul

P.S. happy to report down the road how the Autocraft battery works on my MB if anyone's interested

 

Great news. I'm glad you resolved the issue.