Rkanuch88

Hello, my 2009 C300 sport is really confusing me. I'm pretty mechanically inclined, I'm a mechanic for the army, and I work on all my own cars regardless of the job.

Problem 1: My voltage with car running is never constant. It ranges from 14.2 down to 12.1. When I come to a stop, my voltage will drop down to 12.1 and stay there and my ac will cut off due to the loss of power, then when I start driving again the voltage shoots back up to between 13.5-14.2 and it just jumps around like crazy, and my ac comes back on.
So far I have ordered a new voltage regulator, and the company I ordered from sent me the complete wrong one... so I just changed the alternator instead since autozone had one in stock and it comes with the voltage regulator. After the install, the car still does the same thing.

Problem 2: My temp gauge on the dash moves around like crazy then I overheat. It moves rather fast to about 90 degrees C from cold, then eventually bounces around back and forth then reaches the red and stays there. My initial thought was my thermostat was stuck closed or I had air in the system. I bled the system of all air and the problem persists, so next I took off the thermostat and took the internals out (until I can get a new one to replace it) since atleast if it were stuck closed, it would be open now. I also drained all the coolant, filled with water, ran it for a half hour then drained again, then refilled with new coolant. I bled the system, then took it for a drive. While bleeding the system, I had the heat on and fan on high, but was only getting Luke warm air. Once driving, It started over heating after a short loop around the neighborhood.

The weird thing is, it seems to run okay for the most part until I come to a stop and the voltage drops. Once that happens and I start driving again, the ac comes back on but then the temp gauge starts going up.

Has anyone seen this before? Or could give some ideas on what to do? I'm about to move (army's needs) and need this car for transportation in like a month and as of now I can't take it anywhere!

Rkanuch88

Also, while it's overheating.. both the upper and the lower radiator hoses get rock solid which doesn't seem normal. It feels like they are going to burst

Carsy

This was posted a few days ago. It sounds very similar to your problems.

A new fan module sorted the issue.

When you are in motion the air cools the coolant . When at a standstill you will need your fan running

https://mbworld.org/forums/c-class-w...tor-fan-c.html

Rkanuch88

the fan comes on no problem, it does run on high just about all the time however

tekfoc

Any codes come up ?
Could be a bad ecu

Rkanuch88

I have Carly for BMW as well as for Mercedes and I get codes for a short in the left mirror heater and the right turn signal. It says they both have short circuits but both of them work?

In the engineering menu under historical fualts I get a ton of dtc386 external fan defect. The fan come on high once the car is at operating temp and stays there.

I was just outside making sure I got all of the air out of the coolant system and I realized I'm not getting any heat at all with the heat all the way turned up and fan on high.

Carsy

this may be your problem :-

https://mbworld.org/forums/c-class-w...o-mbworld.html

"Anyone considering jump starting a Mercedes via the battery terminals, Don't Do It!, doing so sends a surge to electrical components and will cause damage.
I'm my instance it burnt out the ac control unit in the dash, lucky I found a used replacement online, if you can find a used one with the same hardware and software codes you can do a direct swop without having a MB dealer reprogram it.
After replacing the ac module the engine fan returned to normal speed and the aircon reset itself and is blowing a blizzard."

Carsy

https://mbworld.org/forums/c-class-w...e-too-low.html

Use the search feature. lots of scenarios!! John

Rkanuch88

I actually have searched high and low through this forum and a few others and haven't found anything. I was messing around with it today, cleaned the outside of the radiator and condenser they're almost perfect but the car is just overheating like crazy. I'm not getting any heat out of the heater whatsoever either. I'm considering selling this car and going back to BMW.