After reading March's article about gear oil,
I felt much more knowledgeable about it.
Coincidentally, I had a family member bring up how poor his gas mileage was in his
1999 Nissan Frontier V6 4x4 with a manual transmission (he was only getting 12 MPG highway). I asked him how many miles were on the vehicle, and he said "oh, only about
60,000, so there can't be much wrong with it." I proceeded to explain in many cases,
and likely his, time is a greater factor than mileage regarding fluid service life and drain
intervals. I explained just because there weren't that many miles didn't mean the 12-year-old lubricants weren't degraded.
I issued him a challenge, and he agreed to let me change his front and rear differential lubricant (MTG), transmission lubricant (MTG) and transfer case fluid (ATF), as
well as his engine oil (OEF). All still had the original fluids, except the engine of course,
where he was using Pennzoil conventional oil. I used AMSOIL Engine and Transmission
Flush in the motor, and poured a bottle of P.i.® in his fuel to ensure his fuel system
was up to snuff. He immediately noticed smoother gear transitions and better speed
retention when coasting out of gear. He just reported to me after a 600-mile trip he
averaged 15.5 MPG. A rather incredible improvement, and a testimonial not only to
AMSOIL, but the necessity of proper fluid maintenance, especially in 4x4 vehicles.
As a second note, his rear differential only drained about a half quart of the original
gear lube, and it holds three quarts, illustrating the effect of volatility over time.
It's safe to say another year and he was probably looking at failure of that gearset; it was a miracle it hadn't already.