Rkanuch88

Hello, I just purchased my first MB and so far it's great. I've owned 3 or 4 audis, 3 bmws, and 2 saabs before and decided to give MB a try. I ended up getting a 2009 C300 sport with the amg wheels.

My car is having a few issues and some help would be excellent. Basically, on hot days while I'm driving the temperature gauge will go from 90 degrees up to 100 then to 105, 110, then back down then back up. It's pretty jumpy. My next issue is that once the car is up to operating temp, if I come to a stop at a red light or a stop sign, with max cool on, once I stop the ac will basically cut off. The blower motor slows down to nearly a stop, but as soon as I begin driving again it starts blowing fast again.

I opened up the engineering menu and displayed the battery voltage while driving today, and when these issues start happening, the voltage goes from a steady 13.5, down to 12.2v and it stays at 12.2 until I begin moving again.

Im kind of cunfused and leaning toward either a defective battery, or a defective alternator. Anyone see this before and can offer some help?

michail71

My temp gauge always stays steady even though when I check through Torque it can vary considerably. I've read that the temp gauge isn't really reporting the actual temps. It must apply some kind of smoothing algorithm.

Given the car's age you could be nearing the end of the second battery the car has had. They can act weird when the battery is old without showing any kind of starting issues.

Rkanuch88

That's the other thing, unless the previous owner had the battery changed at the dealer, this looks like the original battery. I'm going to run to autozone and have them use their bettery tester on it

Rkanuch88

Got the battery checked and it turned out to be good, it was only charged 83% however because the alternator is only pushing out 13.14 volts, and it drops as low as 12.2 volts. Should I change out the alternator?

Carsy

The alternator usually generates above 14 volts when slightly above idle.

System low voltage seems to create weird electrical problems with these cars.

I would seek the services of a auto electrician who knows MB.