All right fellas, here's a little info from my experiences and some of the trivial knowledge I have aquired over the years. And they said it would never matter.

No they will not mix, synthetic blends are manufactured that way, not just put in a pot and mixed together. They may mix to an extent and I don't think it will hurt, but I would change it when I got a chance just because that's how I am.

As far as a manual tranny taking dexron, the big three have been doing this since the late '60's. The three speed stick in my '71 Demon came from the factory filled with dexron. So do all newer sticks and has been pretty standard since the early '80's. Yes, you can empty them out and use gear oil, as a matter of fact my Demon recommended Dexron, but even suggested topping it off with gear oil or refilling after assembly with gear oil if Dexron was not readily available. I know a local tranny builder here in Albuquerque who fills ALL of his rebuilds with dexron after the build, sticks, autos, everything. He says it causes less problems in the long run as most people don't understand that there is a difference in tranny fluids and use dexron anyway.

As far as runnin' it like that? Like I said, theoretically it shouldn't hurt and should be better that being low, however, most of the tranny guys, I know would say change it quick because on their own the synthetic and regular oils are not compatible and won't mix on their own. They would tell me it's like mixing oil and water and it won't work. Same with any oils, don't mix them. Also, don't break your freshly rebuilt engines in with synthetics. You will have problems getting the rings to set properly.

Even though it's lighter, Dexron has better lubricating qualitys than heavier gear oils. Most medium and heavy duty trucks have been using synthetic Dexron for a few years now, and I tend to have to replace less of the new ones with the same amount of use. And I'm talking about eatons and spicers, hard use trannies in medium and heavy trucks. Another thing I have noticed is when we have to replace an older trans in these trucks the rebuilds, from the dealers, recommend synthetic dexrons instead of the gear oil that the failed unit used.

Anyway, enough rambling I hope this helps.