I have 2200 miles on my '04 now and have changed the oil once (1500mi).

I intend to get it to about 5000mi (which will probably take until fall) and then switch to synthetic motor oil. I reckon that's a solid break in period and at that point no wear is a good thing.

My question deals more with the transmission, diff and transfer case lubricants. If synthetic motor oil is proven to cut wear to almost nothing, will synthetics in all other areas (tranny/diffs/transfer) result in almost no wear?

I understand the schedule for changing these fluids is much longer than the engine oil, however, would going ALL synthetic at 5000mi be detrimental in much the same way as putting synthetic oil in the engine might be from too early in the break-in period?

Should I concider putting synthetic in the rear diff. prior to the front? I probably have 20 miles on the front diff right now and by fall, even with some off roading that might only be up to 200 miles.

Any comments welcome.

I changed to all synthetic execpt brake and power stearing at 8k. 16k on it now with no probs at all.
Using Amsoil all around

Going synthetic all around is a good idea, especially if you forge water, etc...as the synthetics won't form emulsions the way the regular dino juiced versons will, and will protect the gears better if you get water in the diffs, etc. (The oil film stays on the metal instead of forming a foamy vinegrette, etc.)

One time I forgot to extend the diff vent tube on my synthetic filled jeep, and articulated under water, popping off the tube, and filling the rear diff with water...

When I drained the diff, hours later, the gears were still lubed/protected.

In the lab, we often ran tests that simulated water in the oil...and the results were pretty consistant...we could add additives to reduce the damage for the dino juice oils...but additives tend to coke out over time, and increase engine deposits, so it was always a compromise between water protection and deposits.

So is it ever too late to change your oil and/or other lubricants over to synthetic ....... I mean, once you get up in milage is there a good reason to change to synthetic? Or, is staying with regular lubricants just as well seeing the milage already on the machine? I guess I am asking if you change to sythetic late in the life of your X, will it be a big deal?

According to the Mobil 1 website, you do not need to wait for a break in period before switching to synthetic oil. They list several manufacturers that use synthetic from the factory. I swear by synthetic oil, and on below zero mornings when my X starts right up and is ready to roll, it confirms that belief. I started using synthetic oils in my wifes 95 Toyota Land Cruiser which has 145K on it. No problems what so ever, even the filler opening looks cleaner! Go for it, it will be the best move you can make for your Xterra.

I started using Mobil 1 in the engine at 10K and changed the tranny, diffs, and transfer over to Mobil 1 at 30K. Haven't had any problems with it yet and its at about 65K. I'll probably change out the diffs and what not again at 80K.

Axle

Synthetics's are a sure fire way to help protect your engine. Mobil 1 boasts being the synthetic oil supplier in such new cars as MB, BMW, Porsche, Jag etc. Yes, those are high performance engines and tend to consistently run at higher rpm's, but the added protection is always welcome in any vehicle. The price of the oil and lubes, usually about 25% more depending on what deal you can find is offset by more protection and less wear from your drivetrain. If you plan on keeping you car to high mileage, then it is an added benefit and peace of mind that will pay off. It isnt some hyped up product, but is actually for real. Consider it as being skid plates and rocker guards for your internal mechanical components; it will prevent damange short of catastrophic failure and prob save you money. I switched to mobil synthetic in my VQ35 path, and run it in all of my other vehicles (its the standard manufacturer oil but still).