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On the Dexron II-III; depends on the application. If you're talking about a transfer case, for example -- you're fine. If you're talking about an automatic transmission -- sometimes yes, sometimes no. The two ATF's have somewhat different characteristics and in certain applications it can make a difference.

On the NV5600 oil -- 75w-90 is NOT a good way to go, and neither is the 5w-30 -- Amsoil or not. 75w-90 is usually a GL-5 rated oil, and will hammer your synchros and yellow metal -- you'll get maybe 50,000 miles out of the transmission before you'll have to rebuild. On the other hand, 5w-30 will not be able to handle the intense shock loads and shear values of the transmission gears -- especially in the NV5600, which pulls heavy loads behind a high-torque engine. You'll end up chipping and cracking gear teeth.

Go with Redline MTL. It's a low-sulphur, GL-4 rated oil with friction coefficient additives for the synchros, and is the best compromise between saving your yellow metal and saving your gears. Royal Purple is also good, but I prefer the Redline product, largely because I've experienced a quantifiable difference in shifting and heat build-up.

GP

Guest

Both DC and New Venture recommend against using any 5w-30 oil in the NV5600. So do most of the major rebuilders and kit-swapper manufacturers. Redline MTL is an &quot;equivalent&quot; lubricant to both 70w-80 and 5w-30 -- which means that it can function as a replacement for either in manual transmission conditions, but has additional properties that both don't have. DC's and New Venture's recommendations for the NV5600 are different than for the NV4500 -- DC's lubricant is a different part number in my manual and in my dealer's books. The recommended lubricant has a low viscosity, is synthetic, and has formulated properties of both a GL-5 and a synchro-specific fluid. <br><br>Redline is usually not sold by local autoparts chains -- it's expensive. You can find it on the web -- Summit carries it, but I use Al Smith's outfit in Baltimore. <br><br>Many people swear by Amsoil products, ratings, and recommendations. Many people don't. The GL-5 yellow metal buffer solution has been tried before by Pennzoil and Mobil, but my information is that the additives tend to break down after a relatively short period. Ultimately the choice is yours --I suppose, with a lot of luck, there are manual transmissions that will run tens of thousands of miles on mineral oil or cod liver oil. <br><br>GP