Mercedes-benz w210 differential oil change (1996-03) e320, e420 pelican parts diy maintenance article gas oil ratio


A differential is just like any other mechanism with moving parts. It generates heat and friction while in operation. Just like in an engine or transmission, regular oil changes help to keep the bearings and gears inside well lubricated and clean. Over time, the differential wears just like any other component. However, it has no internal filter to capture small particles of metal as the gears wear. Also, the differential uses oil that is much thicker than engine oil. Usually, differential oil is good for up to 80,000 miles without changing. However it is commonly overlooked in the wide spectrum of vehicle maintenance. Failure to change the fluid at regular intervals can eventually cause the bearings in the differential to fail. In this article I will go over the simple steps to change the oil yourself and avoid a costly trip to your mechanic for something you can do in under an hour in your driveway. For this job, we are using Redline 75/90W Synthetic High-Performance Gear Oil. You’ll need 1.5 quarts to fill the differential.

First, drive the car around the block a few times to get the oil inside the differential warmed up. The fluid will flow out of the differential easier when it is warm. Now jack up the car and secure it on jack stands at the factory lifting points. You’ll want the car to be as level as possible to ensure that the fluid level is accurate when you fill the differential.

Now crawl under the car and look at the differential. On each side of the differential towards the bottom, you will see two 14mm internal Allen head plugs. These are the drain and filler plugs for the oil. The drain plug sits on the right side of the car near the bottom of the differential. The fill plug sits higher up on the opposite side.

Put a drain pan of at least 2 quarts capacity under the plugs and first open the top plug to relieve any possible vacuum inside the differential and help the oil drain out. Now loosen the lower plug and thread it out by hand. Keep in mind that the old oil will start to flow out as soon as you remove the plug, so make sure the drain pan is directly below. Also, gear oil is some of the worst smelling stuff on earth. If you get any on your clothes, you will never get the smell off again, so be sure to wear your worst work clothes.

Let the old fluid drain out of the car completely. Just watch it, it will go from a full stream to a small trickle then it will stop flowing. Once it has stopped, clean the drain plug threads and apply a small amount of non-permanent threadlocker. Now thread the drain plug back in and torque it to 55 Nm (41ft/lbs.). Now, get the new fluid and pump the new fluid into the filler hole at the top using a siphon. When the fluid begins to flow out of the top hole, it is full. Now clean the filler plug, put a dab of threadlocker on the threads and thread it back into the differential. Torque the plug to 55 Nm (41ft/lbs). Be sure to wipe up any fluid that may have spilled on the exhaust or on the outside of the differential itself.

Got under the car today, e-brake ON. Transmission in Neutral. All wheels blocked and on the ground. Reached under the car and spun the drive shaft by hand. Either direction. Spins freely both ways. The pinion input is spinning. Something must have broke in the diff?

Followup from the Pelican Staff: If spinning free without grinding, the connection may have failed. Usually when a diff fails there is noise, resistance when turning or grinding. Pull some fluid out of the diff to check for metal. – Nick at Pelican Parts

Comments: I have a 300e that was low on differential oil and caused a vibration when taking off. It’s full now and doing better, but it still has a slight vibration when taking off. Why is it doing this and what do I need to replace? Thanks.

Comments: I’m planning on replacing the differential oil in my 96 E320, so I naturally read through this article. My question is regarding the replacement oil. I see other oils out there that are synthetics like Mobil 1 75/90 or Motul 300, 75/90 gear box oil. Is there a better oil than the stock replacement oil? What do you recommend?

Followup from the Pelican Staff: I always stick to factory fluid. You can however sometimes improve on it. As long as the fluid is approved by MB. Give our parts specialists a call at 1-888-280-7799. They can help you find the right fluid. – Nick at Pelican Parts

Comments: Great pix, easy to follow! Thanks a million, Wayne! The only thing I’d add is, this is a difficult task if you can’t get the car off the ground. There just isn’t enough space to work. Elevate the car with whatever you have, and be safe.

Comments: the drain plug 14 mm was stripped by the previous owner and I can’t get the plug out. Should I use a cold chisel and beat it out or is there a more civilized say? Also I looked for the "Vent bolt" on the top of the chunk and didn’t see one, is there one? The car is a 77 Mercedes 450 SLC. Your expert advice is welcome. Where can I purchase a "Plug" once it comes out?

Comments: I think your differential will start whining as the bearings wear out, and the noise will increase as the condition worsens, so a minor and intermittant noise is not a sign of imminent sp? failure. This is a useful tech article, but it omits the most important reason to remove the upper plug first, which is to be certain that you will be able to re-fill the differential case after you drain the old fluid. The last time I did a differential fluid change, I used an L-style hex "allen wrench" in the plug, and used a box wrench to turn it.

Comments: Your directions are very detailed an sounds easy but I would like to know what the "Replace differential mounting bushings" looks like and how do I even find it from your parts list? Because, I couldn’t find it maybe because I don’t know what it looks like? by-the-way. I have 2002 E320 4matic. Thank you.

Comments: I was told by jiffy lube 8-31-13 when having an oil change that I neeeded rear differential. It was my 1st time ever hearing those words in reference to my vehicle a 1990 300E 4door sedan mercedes. He said fluid was little to none so he replaced the fluid but advised rear differential asap. I’m only now able to afford to have rear brakes done & have rarely been driving it. The noise still continued even after oil was replaced the noise only occurs when I 1st start up the car for the day & put it in drive & barely push on the gas it has a rumbling noise for about 2 seconds then stops. I’m having rear brakes pads replaced tomorrow what should I expect from the mechanic when I explain the differential situation to him? Please advise!

Followup from the Pelican Staff: If the noise is truly from the differential (and not the rear brakes or wheel bearings) then all you can do is either replace the differential now or wait until it seizes. Depending on amount and intensity of use, the diff could go years and just make more and more noise until it seizes. – Nick at Pelican Parts

Followup from the Pelican Staff: I hope the vibration is from a worn center bearing in the middle of the driveshaft. Drain and refill your rear diff with gear oil and see if the noise goes away. If not and the fluid level was low you may have already damaged the diff by running it low on oil. A professional mechanic would lift the car till the wheel were off the ground and use a stethiscope or an "engine ear", start the car put it in drive and accelerate a little and listen for the rumbling. An older mechanic would do the same thing but hold a long screwdriver against the diff or spindle (NOT A ROTATING PART)and put his ear against THE OTHER END OF THE SCREWDRIVER and reposition the screwdriver until he isolated the noise. Running the car on a lift requires some skill in setting up the car so vibration will not affect it. – Kerry at Pelican Parts