Anybody knows what type of fluid the 6spd uses? I'm thinking about replacing it with Redline MTL. Anyone tried this yet?<br><br>Thanks<br><br>MikeyB

 

Search the 24 valve engine/drivetrain forum and the &quot;other&quot; site, this is a popular topic and is as controversial and lengthy as any of your &quot;Why isn't Amsoil API certified?&quot;/&quot;Ford owns Cummins&quot;/&quot;How often should I change my oil?&quot; threads.<br><br>The only fluid other than the Mopar fluid (which by the way says on the bottle that it is specifically blended for the NV-3500 transmission) that STATES ON THE BOTTLE that it meets the Mopar MS-9224 specification is a Penzoil product that has been seen at Auto Zone. If you poke around in an old enough thread you will also see references to a Texaco product that is no longer made.<br><br>That said, if you search the threads you will find folks are using products from Amsoil, Redline, Royal Purple and everything from gear lube to 5W-30 motor oil. Apparently there are issues with the metal used in the sychros that can be deteriorated by the wrong fluid, and the fluids that are best for shifter &quot;feel&quot; are not necessarily good for the synchros.<br><br>To make a long story longer I am in no way qualified to render an opinion on your specific question. I am satisfied with the factory fluid in mine (although it took 20 ounces to top it off after I received the truck) I do not have the notchy shifting or the third gear grind that I have read about. Look around, there are a lot of opinions out there.<br><br>Good luck.

 

The Ford guys at the diesel stop are asking the same ???'s for the ZF6.<br><br>Here's my non-answer comment. I've spent a fair amount of time draining fluids out of my cars and truck transmissions (syn, dino, oil, fluid), But; after spending $30+K on a brand new vehicle inside the warranty window, I'm gonna stick with the OEM recommendations (found in the Owners Manual). I have some of those aforementioned oils/fluids in my car and boat - and I like them. But the Blue Beast will follow OEM for now.<br><br>I'm an engineer, but not a ChemE; and even then wouldn't relish a grueling interrogation ordeal with DC Warranty folks if in fact something happened inside my tranny and I had decided to use an &quot;improved&quot; oil/fluid in proving my case. Can it be done? Sure. But my life is busy enough, why add an unnecessary variable?

 

It's my understanding the factory fluid in the NV5600 is &quot;fill for life.&quot; However, as we know, that isn't necessarily the case in the real world, as things can happen.<br><br>Red Line MTL would be an excellant choice. It's a GL-4 rated lube. GL-4 usually contains about 1/2 the sulfur/phosphorus anti-wear content of a GL-5 lube. Sulfur has been known to attack yellow metals, ie synchros, at high temperatures. Some claim this isn't an issue with a synthetic lube as they tend to run cooler. GL-4 will also provide better &quot;traction&quot; for the synchros. <br><br>Most other gear lubes I've researched are rated GL-5. I know Mobil 1 specifically states not to use their GL-5 synthetic gear lube in transmissions calling for a GL-4 lube.

 

The 6-spd doesn't use heavy weight gear oil. It uses something similar in consistency to motor oil. GL-4 and GL-5 are gear oil specs, are they not?

 

Red Line MTL is a lightweight GL-4 gear oil. It says to have low temperature shiftability equal to an ATF and will not thin out at high temperatures. ATF atypically is a 20W oil. The higher synchronizer coefficient of friction of MTL allows faster upshifting and downshifting, and is non-corrosive to synchros and bushings.<br><br>MT 90 is their heavier transmission oil, which is a 75W-90 GL-4 lube. That would be indicated for the NV4500 5 speed transmission.