Keep in mind that MOPAR stopped supplying their branded version of the Castrol Syntrax Limited Slip 75W-140 somewhere around 2018-2019. It was NOT listed in the pdf version Chrysler/MOPAR “2020 Vehicle Lubricant & Chemical Catalog”. While a few bottles existed at some dealerships, many of us had already started buying the Castrol version directly from Mercedes dealerships that came in metric equivalents of pints and quarts…at an excellent price. The pint size (actually 500 ml) has a very handy extendable spout. INTERESTINGLY, this Castrol Syntrax Limited Slip 75W-140 has now disappeared from many Mercedes dealerships…and, from Castrol’s online product list.
The latest Castrol differential product for Mercedes AMG’s, BMW M series, Nissan GTR’s, and PRESUMABLY Gen V Vipers that supersedes the Syntrax Limited Slip 75W-140 is Castrol Transmax Limited Slip LL 75W-140. The container looks like the Syntrax…with the same cool spout on the 500ml bottles which sell for $26.75 apiece retail (tax included) here in Indy today. While it puzzles me that Castrol picked the name “Transmax” for a differential lubricant, the Castrol Tech Supporyt Help Line in the UK who I contacted by telephone TODAY assured me that the Transmax Limited Slip LL 75W-140 is an IMPROVED lube for our differentials.
IMPORTANT RECENT DISCOVERY by Viper Wizard Chuck Tator (Owner of Tator’s Garage…Head of VOA Tech Committee):
While preparing to use some of the original MOPAR “SAE75W-140Gear and Axle Lubricant” in a Gen V Viper differential, Chuck noticed that this “fluid” had turned to “jello”, with lumps, and a gritty precipitate was also noted. THIS IS MOST ALARMING as many (most ??) folks that I know generally squeeze these bottles by hand to fill the differentials directly without the potential mess of using a transfer pump. So, WHO would know the status of the fluid ?? Unfortunately, the fluid that Chuck had purchased from a dealership had no discernible date codes…so the actual age was/is unknown. Chuck got rid of the whole lot.
When doing a little lube research, I found that a general rule of thumb for these fluids is that they have about a 5 year shelf life. Fluid and lube EXPERT Tom Hayden was kind enough to give me a short tutorial on these types of products…noting that this is complex chemistry. Tom MAY get in on this thread in the near future…and if he does, please LISTEN to his advice and explanations. By the way, during my conversation with Castrol UK today, they indeed confirmed the 5 year shelf life of these products…noting that once the container has been opened and resealed, it must be used within 2 years or discarded.
WITH the background information updated above, I PERSONALLY would RECOMMEND that Gen V owners use only Castrol Transmax Limited Slip LL 75W-140 purchased at one’s local Mercedes dealership…paying strict attention to the date code on the bottle before purchase and use.
If you have a supply of the older Syntrax with date codes less than 5 years, I would only use it after decanting it (like a bottle of wine) into a clean, clear container to check for separation of the contents, thickening of the fluid, and/or precipitation of components .
If you have some of the discontinued MOPAR fluid, I would NOT USE IT and would merely discard it in the appropriate fashion.
Unless RP substantially changed their formula they would be one of my last choices. You can Google testing results of differential fluid. We called RP products a boutique oil. Lots of effective marketing. Don’t know why one would not accept Steve-Indy’s post as fact.
FYI I do use a RP oil filter in my Ram 6.4L. My choice is based on testing results not marketing.
Thanks Steve, just had my rear diff service and I showed Fred Ragel ( Viper Tech ) at Woodhouse Dodge your info. They only have the new fluids , but still good data to have in case someone brings in old fluid they bought and stored years back.