When transfer case oil should be changed?
A transfer case is an important part of the vehicle four-wheel drive system. In pickup trucks and truck-based SUVs, a transfer case is a large mechanism attached to the rear end of the transmission (see the photo). It may contain a central differential, low-range gearing and other controls of the 4WD system.
Most compact and mid-size all-wheel drive SUVs and crossovers have a smaller transfer case (see photo below) that is often called a power transfer unit
. A transfer unit simply provides power output for the rear axle. Regardless of the size, a transfer case or unit is filled with and lubricated by a special fluid or oil. How often should transfer case fluid be replaced? A lot depends on the use of the vehicle. For example, the maintenance schedule for the 2017 Toyota RAV4 recommends replacing transfer case oil every 15,000 miles if the vehicle is operated in special operating conditions. These conditions include driving while towing, using a car-top carrier, or heavy vehicle loading. For normal driving conditions, Toyota recommends only inspecting the fluid every 15,000 miles, but doesn't mention replacement.
For the 2017 F150 pickup truck, Ford recommends changing transfer case fluid every 150,000 miles for normal driving conditions and every 60,000 miles when towing a trailer, operating in dusty or sandy conditions or off-roading.
What if you only do normal city and highway driving and your maintenance schedule doesn't mention transfer case fluid change for normal conditions? Can a transfer case last a lifetime without fluid change? Unfortunately, it's rather a wishful thinking than a reality. Any mechanical device with moving and rotating parts is subject to wear. In addition, in many cars, a transfer case is located close to hot exhaust components, which causes the fluid to deteriorate sooner. See this photo
of an inside of a failed power transfer unit at 105,000 miles.
As recommended by car manufacturers, a transfer case should be checked regularly for leaks. If signs of leakage are present, it should be repaired as soon as possible.
In our opinion, for normal driving conditions, the transfer case fluid should be replaced at least every 60,000-70,000 miles or sooner if so recommended in a maintenance schedule. The fluid also should be changed if a transfer case has been submerged in water. Your mechanic may suggest checking the fluid condition first and change it if it's dirty. Typically a transfer case or unit has two plugs: a fill plug above and a drain plug at the bottom. The fluid level and condition can be checked through the fill plug.
In most vehicles, a transfer case is filled with gear oil 75W-85, 80W-90 or 75W-140 grade. You can find details in the "Specifications" section of your owner's manual. A transfer case fluid change costs form $120 to $250 in the repair shop.
We have included links to manufacturer's websites where you can check the maintenance schedule at the bottom of this post.