alexi_k

Good evening, members.

I've tried to source a thread on changing the rear differential oil of a CLK - 209 series. I could not find a sticky note on this. If there is a thread on this, apologies for the re-post.

Can one advise as to when this must be done (every x years or x kilometres?)

I drive a 2007 Mercedes-Benz CLK 500 (M273, 5.5L) which currently has 83 400km's on the odometer.

Thanks in advance,

Kind regards,

Alexi

kb24forlife24

Every 6 years or 39,000 miles

Kelvin Bellrose

What is the recommended oil? 80w90 full synthetic?

JoiseyBenz

Best place to look for this answer is in your owner's manual. If you don't have one, you can easily find a pdf copy on the internet, perhaps even on the MB web site.

On my 2006 CLK500, the book says "Hypoid Gear Oil, SAE 85W90". I ended up using "Mobil-1 75W90 Synthetic". You'll probably hear 5 different opinions from 4 people. You have to decide for yourself what is best. You certainly can't go wrong using whatever your manual says. Up to you.

OR-CLK350

My experience w/lubricants has been that it is better to buy them at the dealer, and generally are not that expensive... specially something that needs changing every 6 years - BTW don’t forget to change the oil fill plug.

You can find the instructions here:

http://benzbits.com/w203/

Audi Junkie

Mobil 1 75w-90 is unbeatable.

alexi_k

Thank you, @kb24forlife24

Nektopoli

I bought the Lucas, not opened yet so I can take it back, can you tell me what I'm looking at? - NP

Audi Junkie

Yes, just in time. This is a AMSoil corrosion test of various GL-5 gear oils. Lucas is always a poor performer in the lab, with Royal Purple not far behind. There's some wear and sheer tests that I didn't bother to save, but yes....Mobil 1 is ideal, and usually the actual oem fluid in many cases. SynPower or another mainstream brand can be fine too, and I def recommend AMSoil or Redline in all cases.

Redline has a nice library of lube White Papers...

https://www.redlineoil.com/technical-info
https://www.redlineoil.com/Content/f...Tech_6.20_.pdf

I'm not even that picky with GL-5 gear oils, but GL-4 Manual Trans Fluids, that's worth "worrying" about. 9/10 times the answer there is Pennzoil Synchromesh from a practical standpoint, but the Redline MTFs are excellent, if not the best.

https://www.redlineoil.com/Content/f...Tech_6.20_.pdf

https://www.pennzoil.com/en_us/produ...ion-fluid.html

Mercedes don't have a lot of MT cars, but watch out for "tuner" retailers who want to put 75w-90 in a manual trans! Often they are using GL-5 or a combo product that is too slick for synchronizers and too thick compared to modern MTF, that is as thin as ATF or even thinner!

Back to gear oil, yes Mercedes back speced to an 80 or 85 weight gear oil, but 90 is still fine. Redline has a range of thinner gear oils and info on their tech pages.

Nektopoli

Thanks for the quick reply and I should have put this in my 1st message, but what about the GL5 vs GL4, for a rear diff on a 07' W203. Is the GL rating interchangeable? - NP

Audi Junkie

People think the GL-4 and GL-5 supersed each other, like one is better than the other. The specs just describe different kinds of gear oils for different tasks. GL-5 for gears is as slick as possible, and has other requirements like corrosion resistance. It's "FM" additives makes it a "friction modified" gear oil for diffs. Other types are for limited slip for gears that run at right angles....etc. Just like we have different ATFs, including ones for CVT, etc...

GL-4 is different simply because of limited use of FM additives, solely so the shift synchronizers are able to grab onto each other and spin-up for the next gear. GL-5 makes a mess of this process. Combo GL-4&5 fluids like Royal Purple are not ideal for either....ask AMSoil or Redine! That's why there are separate products, like Pennzoil Synchromesh ONLY GL-4.

Nektopoli

I noticed one was GL5 wasn't recommend for gearboxes, so I worried it would be recommended for the rear diff, this is the statement that got me posting here;

"GL-5 has roughly twice the amount of EP additives compared to GL-4, which is why it is often used in high-pressure circumstances such as in a front axle and rear axle differential. Sulphur/Phosphorus additives however have an unfavourable property: they can react aggressively towards bronze and copper. This can be disastrous for the synchromesh rings of a gearbox. Therefore it is not recommended to use GL-5 in a gearbox unless the manufacturer allows this."

Thanks again ! ! ! - NP

Audi Junkie

Yes, by "gearbox" they mean a manual transmission. I know it's confusing.

The notion that sulphur/phosphorus additives will corrode yellow metal parts, like bronze synchros is very out dated. Those type adds aren't used since 20 years ago.

There's an "MT-1" spec from API that indicates a fluid is safe for yellow corrosion...
https://www.oilspecifications.org/api_gos.php

Audi Junkie

For absolute clarity: GL-5 is for differentials and is usually called "gear oil" or for "axles", GL-4 is for manual trans "gearboxes". The only difference being the coefficient of friction.

https://www.pennzoil.com/en_us/produ...le-75w-90.html
https://www.pennzoil.com/en_us/produ...ion-fluid.html