How trustworthy are MFG Cross Listings?

S

SubieNate

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May 7, 2014
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My car (Chevrolet SS Sedan) specifies this in the manual for the rear differential:

IMG_8433.webp


I have been a big fan of Ravenol fluids for a while and they cross list their DGL and MDL oils for this GM number but only MDL for the Castrol SAF BOT 720 that has superseded the Carbon Mod.

https://www.ravenol.de/en/properties/empfehlung/gm-92184900

The SS and Pontiac G8 enthusiast forums are very convinced that the carbon mod/GM fluid has special sauce friction modifiers for our carbon based diff clutches. I’ve been told I’m going to ruin my diff. Stateside, it appears Redline and Royal Purple think you can use their fluids but AMSOIL has specifically told people to use the OE fluid.

I usually trust that the chemists at a place like Ravenol know what they’re doing when they say it meets a spec, but wanted to see if the experts here could weigh in. It literally has my spec printed on the bottle, but the volume (and volume) of comments I’ve gotten saying I’ve made a mistake make me nervous.

As a secondary question, if a fluid has multiple cross listings as in this case, is there a “best” way to choose between the two?

Cheers,
Nathan
 
MDL appears to contain a lot of PAO, judged by the density being low. PAO will do nothing to carbon anything.

DGL is thinner and seems to be made for manual transmissions with synchro's and LS differentials.

I'm not sure anything special is needed for those clutch packs; you just don't want very high solubility, like a group I mineral or ester based lubricant could have.

I would go with MDL unless you intend to use the car at extremely low temperatures (like -20°F and below).
 
Yes I initially picked the DGL because it seemed like a more standard friction modified gear oils and had the same viscosity range on the bottle as the stock requirement. The MDL also didn’t say GL5 anywhere.

FWIW Ravenol claims the DGL is also primarily PAO.
 
Really did a deep dive on this last night and found the below document from ZF, who makes the diff in this car:

https://www.zf.dk/wp-content/uploads/te-ml_18.pdf

Screenshotted below with the Carbon Mod fluids highlighted (Mine double highlighted).

1733024332090.webp


Doing a little legwork, here are all the cross references for the OE specs for the two Ravenol fluids that claim to meet the GM/AC Delco PNs:
1733025925311.webp


In addition to the above, Land Rover BOT 720 is thought to be the superseding castrol fluid, and it is listed under MDL on the Ravenol Site. Lots of land rover guys buying the GM bottled stuff for half the cost of their fluid.

Clearly Ravenol believes that both of these fluids are A-OK for these carbon based clutches, because they're cross listing both of them for multiple makes/models that use these ZF based carbon clutch diffs and for more than one application they are cross listing both.

I would love to talk to someone technical at Ravenol to understand how they come up with their cross listings, and why 5 or 6 OE fluids (6 if you include the Land Rover stuff) that are, according to ZF, rebottled Castrol SAF Carbon Mod seem to be randomly distributed between these two fluids.

The other cross listings I have found for the GM/AC Delco fluids are from Royal Purple, Penrite in Aus, and Redline, and in all three of those it's just their 'standard' LS GL5 in the 75W85 spec. YMMV.

For my money, I am going to put the OE fluid back in it for now and consider the ravenol fill a flush, but in the future I'd buy the MDL with no worries regarding the compatibility, and if I couldn't get that, I wouldn't fret putting the DGL in it. Why the MDL over the DGL? It's technically cross listed for more of the applications, and it's specifically for multi disc clutch type diffs.

I'd be putting the Ravenol MDL in it now if Blauparts had free shipping.

Cheers,
Nathan
 
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