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Pelican Technical Article:

Alternator Replacement

Time:

1 hour1 hr

Tab:

$200

Talent:

**

Tools:

10mm, 13mm, 15mm sockets, screwdriver

Applicable Models:

Mercedes-Benz W210 (1996-03)

Parts Required:

New or rebuilt alternator

Hot Tip:

ALWAYS disconnect the battery before beginning

Performance Gain:

Car charges again

Complementary Modification:

Change serpentine belt

The alternator charges the battery and provides your car with a constant source of electricity while the engine is running. Over time, the alternator will begin to fail and cause trouble with the various electrical devices in the car. If you suspect alternator trouble, you need to check to see that is operating correctly, and is indeed the cause of the problems with your charging system. Sometimes bizarre electrical problems can be caused by a number of faults other than the alternator. It's important to troubleshoot the system prior to replacing your alternator.

The first thing to check is the battery light on the instrument cluster. This light bulb is part of the alternator field circuit; if it burns out the alternator will not charge. Simply turn the key on and see if it illuminates briefly then goes off. If the light does not illuminate, you'll need to replace it before continuing.

Inspect the belt that drives the alternator. Is it tight and amply turning the fan? If not, then check that the belt tensioner is working correctly. Modern belts seldom break, but they get brittle and glazed with age, and can slip on their pulleys. Replace the belt with a new one as required.

The next item to check is the voltage at the battery. This should read a little more than 12 volts with the engine off. Wait two minutes after starting the vehicle for (accessory cycling) voltage to stabilize. When the car is running, the voltage must read in the range of 13 to 14.5 volts with the engine at 3000 rpm. If your battery appears to be leaking, then your voltage regulator has probably failed. The battery will usually only leak acid if it has been overcharged at a much higher voltage. If the voltage measured at the battery is more than 15.5 volts when the engine is running, then the regulator is probably bad. If your battery has boiled over and has acid overflowing out the top, make sure that you clean up any spilled acid immediately. Dousing the area with a water and baking soda solution should help considerably to neutralize the acid, and prevent it from eating away at the metal.

An important item to check on your car is the engine ground strap. The engine is electrically isolated from the chassis by rubber motor mounts. If the engine ground strap is damaged or disconnected, you will have problems, including electrical system malfunctions, no and/or difficult starter cranking.

If you've checked all of these things and you still have charging problems, it's likely the alternator will need to be replaced. The first step in replacing any alternator is to disconnect the battery. You will be working around live electric wires here. If you happen to touch the lead going to the alternator against something, you can cause permanent damage to the electrical system if the battery is hooked up. Be smart here and disconnect it. Please refer to our article on battery replacement for more info. Also remove the air filter housing from the car. This will give you a bit more room to remove the alternator on some cars. Refer to our article on replacing the air filter for more info.

Shown here is a rebuilt alternator.
Figure 1

Shown here is a rebuilt alternator. Typically, you'll need to transfer the pulley from the old alternator onto the new one. Rebuilt alternators usually include a core charge. That means that a fee that is refunded to you after you return the old alternator. The old alternator is then sent back to the company to be rebuilt.

Remove the two spring clips that hold the fan shroud in place on the top of the radiator support (green arrows).
Figure 2

Remove the two spring clips that hold the fan shroud in place on the top of the radiator support (green arrows). Pull the coolant line going to the expansion tank out of its groove on the fan shroud (purple arrow) and carefully pull the fan shroud up and out of the engine compartment. This will give you a bit more room to work with.

On the back of the alternator are two electrical connections.
Figure 3

On the back of the alternator are two electrical connections. One is a 10mm nut and the other a 13mm nut (green arrows). Remove the nuts and pull the connector off the terminals.

Locate the serpentine belt tensioner to the left of the radiator fan.
Figure 4

Locate the serpentine belt tensioner to the left of the radiator fan. Use a 15mm socket to rotate the tensioner pulley clockwise. This will loosen the serpentine belt and allow you to remove the belt from the alternator pulley. In this picture, you are looking down at the ratchet sitting on the tensioner nut.

Remove the serpentine belt from the alternator pulley and locate the two 15mm bolts that hold the alternator in place (green arrows).
Figure 5

Remove the serpentine belt from the alternator pulley and locate the two 15mm bolts that hold the alternator in place (green arrows). Loosen and remove the bolts. Keep in mind that these are rather long and you may need to turn the radiator fan to get clearance to remove the lower one. Also, keep one hand on the alternator itself when you remove the bolts to keep it from falling. Once the two bolts are removed, maneuver the alternator out of the engine bay.

Here's a shot of the engine compartment with the alternator removed.
Figure 6

Here's a shot of the engine compartment with the alternator removed.

Shown here is the old alternator next to the new one.
Figure 7

Shown here is the old alternator next to the new one. You'll need to transfer the pulley from the old alternator (green arrow) to the shaft on the new one (purple arrow). The best way to go about this is to use an impact wrench on the pulley nut.

Transfer the pulley to the new alternator and use the new 24mm nut and lock washer, secure it to 80 Nm (59ft/lbs.
Figure 8

Transfer the pulley to the new alternator and use the new 24mm nut and lock washer, secure it to 80 Nm (59ft/lbs.). Re-fit the two 15mm bolts that hold the alternator in place and torque them to 42 Nm (30ft/lbs.). The 10mm electrical connection is torqued to 4 NM (2ft/lbs.) and the 13mm electrical connection is torqued to 15 Nm (11ft/lbs.). All that's left to do is refit the serpentine belt, fan shroud, and then reconnect the battery.

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Comments and Suggestions:
Bricedes Comments: 1995 s320 im wanting to replace my alternator, are other model alternators compatible?
March 3, 2016
  Followup from the Pelican Staff: Just the alternators for you vehicle, none other I know.
Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Dillon Comments: I have a 1992 mercedes benz 300E. I'm replacing the alternator. Do I need to remove the radiator to get to the alternator?
February 18, 2016
  Followup from the Pelican Staff: I don't believe so, but I am going by memory. - Nick at Pelican Parts  
BenzBoi223 Comments: In figure 5 and 6, where is the wire next to the radiator hose going from end to end? I think I broke it while removing the alternator but the car still runs fine...
February 17, 2016
  Followup from the Pelican Staff: I think it runs to the starter cable. Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
cal Comments: My 2001 Mercedes E320 4matic remove key light and beeping stays on when the car is running, also I have a new battery, alternator and serpentine belt but the battery is still not charging
December 26, 2015
  Followup from the Pelican Staff: The EIS may be faulty, recognizing a key when none is present. Also causing the battery drain. - Nick at Pelican Parts  
cal Comments: my remove key light and warning system beep stays on when the car is running , also I have a new battery and alternator but the battery is not being charged
December 26, 2015
  Followup from the Pelican Staff: The EIS may be faulty, recognizing a key when none is present. Also causing the battery drain. - Nick at Pelican Parts  
Ben Comments: I have a 1997 non turbo diesel and I want to upgrade the alternator. Will the alternator from the turbo model fit without modification to the brackets to the non-turbo?
December 10, 2015
  Followup from the Pelican Staff: I don't think so. To be sure, check if the part numbers match. - Nick at Pelican Parts  
MAS75 Comments: My 1996 E300 Diesel when dark on me yesterday. I parked the car in the morning at work and left the keys in the ignition by accident. They car was in park and the e-brake was on. I cannot verify if I left the key in the on position, I moved it before thinking. But know the car is completely dead, no electronics shown any sign of life. No blinking green/red lights unlock lights, nothing on the dash lights up when I insert the key. Had to push down the locks on the car doors last night hopefully this doesn’t hurt the airlock system and use the key to lock the driver’s door and trunk.

Any suggestions on what to look at would be helpfully.
October 14, 2014
  Followup from the Pelican Staff: Try jump starting the vehicle, then letting it run for a while to recharge the batteries. Check your owner's manual for instructions. - Nick at Pelican Parts  
vietnamvet43 Comments: The charge battery light comes on and sometimes stay on after the car is turned off. The battery is new ,I get 13.6 volts across the battery while idling and a little over 12 volts when off also I am not getting ac voltage. Sometimes the car keep running after I turn the ignition off. Could I still be needing a voltage regulator or do I have other problems ?
January 28, 2014
  Followup from the Pelican Staff: This could be a fault with the ignition switch or another component backfeeding voltage. You will have to check voltage from the ignition switch to confirm it is turning OFF. - Nick at Pelican Parts  
Sillaw Comments: My 2006 ML 320 CDI went into a melt down after the battery warning light appeared.
The dealer tells me the alternator overcharged the battery and both have to be replaced along with the SAM unit, whatever that is and then there is a pulley belt which was cracked and an earth lead and they also say the harmonic balancer was loose but not related to the electrical troubles all adding up to a budget deficit the size of a small European country.
Should all this happen on a six year old car costing well over $100,000?
It is serviced regularly and driven average kilometers mostly on long trips.
June 10, 2013
  Followup from the Pelican Staff: I hope this DIY saved you some money.
All of the listed failures are common maintenance items.
Repair work after the factory warranty expires, is always HIGH at the MB dealer.
For discussion of Vehicle cost/value, I recommend Jeremy Clarkson, Richard Hammond, and James May
Top Gear http://www.topgear.com/uk/

-whunter-
 

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