Synthetic oil is not only recommended by DC, it's the factory fill the vehicle comes with. You may void your warranty -- if you still have one -- by *not* using synthetic. The synthetic should be the equivalent of 70w-85. Do not use a GL-5 rated oil, as they contain various shear and pressure additives that will destroy your synchros in a few tens of thousands of miles. Use a high quality GL-3/4 synthetic, instead.

I use Redline MTL, and it's nearly eliminated the infamous second-to-third gear grind when cold.

MM's right, when you change the oil, make sure to locate, remove, and clean the big magnetic pad on the bottom of the transmission case, between the PTO plates. It'll have a lot of metallic gunk on it.

And I agree with MM on the Fastcoolers. They're more than I would've liked to pay, but they do increase the capacity to levels I'm comfortable with. Actually, I mounted a single Fastcooler on the NV5600, and put the other Fastcooler on the PTO access to the NP241HD transfer case. On the other transmission PTO plate (passenger side), I've mounted an Eton transmission filter housing from Geno's. The combo works well.

GP

 

The NV-5600 holds 4 quarts - requires a MS-9224 spec oil - you can get it at the Dodge dealer for $10 a quart - Redline has it, and so does Pennzoil - tho' I've yet to find any of the Pennzoil stuff in any of the local outlets...<br><br>Engine oils are NOT usually adequate for manual transmission use - the operation and stresses in a transmission and it's syncronizers are substantially different than that of an engine...<br><br>Redline, on their website, and commenting on proper lubes for the NV-5600 says THIS about use of engine oils in the 5600...<br><br>============<br>These lubricants are not well suited for transmission use because of two factors - shear stability and improper coefficient of friction - which will be discussed in more detail later. At even lower temperatures such as -17.7°C (0°F), the differences between conventional lubricants and Red Line MTL are even more dramatic. At such a temperature many of these lubricants would prevent shifting into certain gears, depending on the design of the transmission. <br><br>All oils are slippery, and with most lubricated components, the slipperier the better, but this is not so with manual transmissions. The synchronization of shifting gears requires friction to transfer energy from the synchronizer, which is locked to the input shaft, to its mating surface attached to the gear to be locked in as the drive gear. Few modern transmissions use sliding gears to change gearing other than for reverse gearing. Synchromesh transmissions have the gear pairs constantly in mesh. The drive gear is selected by using the shift forks to slide a synchronizer ring, which rotates at the same speed as the input shaft, in contact with the selected drive gear. Once the drive gear is brought to the same speed as the input shaft, the locking ring on the synchro assembly is allowed to slide over and lock into the drive gear. <br><br>The time this process takes depends on how easily the synchro ring moves and the rate of frictional energy transfer between the two synchronizer surfaces. Higher viscosity lubricants slow the sliding of the synchro ring on the input shaft and require a longer time for the oil to be squeezed out from between the mating synchronizer surfaces. After the lubricant is squeezed out, the coefficient of friction of the lubricant determines the rate of frictional energy transfer between the two surfaces. Slippery lubricants such as hypoid gear oils and ATFs can take too long to synchronize the gears, which promotes synchronizer wear. Red Line MTL and MT-90 has a coefficient of friction which is greater than conventional oils, allowing a quicker transfer of frictional energy. <br>===============<br><br>SO, use yer own judgement as to what to pour in yours...

 

There are several cases where folks figured their 5600's weren't shifting to suit them - and they switched to different &quot;magic cure&quot; lubes - including 5w-30 engine oils...<br><br>In SOME cases, shifting was apparently improved - but at what long-range cost? There is a specific spec for lubes in these trannies that addresses MANY wide range areas of importance - ability to flow properly in the cold - or heat, shear stresses, detergency, lubricity to protect against wear while ALSO providing for proper syncro operation - the list goes on, and MANY of those aspects might not be readily apparent until you get close to the ragged edges of the tranny's ratings - like towing a heavy trailer up in the Colorado Rockies on a hot day - THEN, that easier shifting ability MIGHT not be as important to you as shear ratings and hi-temp survivai that WEREN'T important to you down in the valley when all you were hauling was groceries...<br><br>Make sure you get a TOTALLY capable lube - not merely a substitute or compromise that may provide more potential problems than cures...<br><br>&quot;Yeah man, my 5600 shifted REAL good with that magic lube.... for about 30,000 miles, then the syncros were shot - and so were most of the bearings...&quot;