Auto-Trak II Transfer Case Fluid is a specialized lubricant developed primarily for the transfer cases of General Motors (GM) four-wheel-drive vehicles. It is composed primarily of hydrotreated neutral oil-based lubricating oils (80-90%) and specific additives. While its viscosity is similar to standard Dexron III or Mercon fluids, it is distinguished by a proprietary additive package.
This fluid is engineered to handle the unique demands of automatic four-wheel-drive systems (often found in GMT-800 platform trucks) where the system must sense wheel slippage and engage internal clutches. Its primary functions include protecting clutch packs, preventing shudder, and protecting transfer case components under high heat.
Using regular ATF is generally discouraged as it lacks the specific friction modifiers which can lead to viscous coupler failure or “toasted” transfer cases.
Side note: Keeping the transfer case healthy is vital for these high-mileage rigs. Owners should also stay ahead of engine-side maintenance by monitoring 5.3 common oil leaks that frequently occur in the same GMT-800 era vehicles.
Auto-Trak II Transfer Case Fluid Alternatives
Below are aftermarket fluids that claim compatibility with GM specification 9986186.
TRIAX DTF-2 Professional 75W-85
TRIAX DTF-2 Professional is an aftermarket full synthetic differential and transfer case fluid formulated as a broad-spectrum replacement for multiple OEM specifications, including GM Auto-Trak II applications.
This 75W-85 fluid is built around synthetic and ester base oils with integrated friction modifiers for limited-slip differentials and transfer cases. It’s designed for front differentials, transfer cases, and gear cases requiring API GL-5 specifications with controlled slip capability.
TRIAX markets this as compatible with GM specification 9986551 and multiple Chrysler/Dodge/Jeep part numbers (68083381AA, 68378949AA, 68237820AA, and others), along with Ford WSS-M2C942-A. The viscosity satisfies SAE 75W-80, 75W, 80W, and 85W requirements.
At 100°C, the kinematic viscosity is 12 cSt, which is higher than Auto-Trak II’s 7.3 cSt. This viscosity difference matters in applications where precise fluid characteristics are critical.
Very important: Do not use this in manual transmissions or transaxles with synchronizers. The friction modifiers will cause uncontrolled slippage and synchronizer engagement problems.
Other compatible applications:
- BMW/Mini (multiple part numbers including 83 22 2 295 532)
- Mercedes-Benz (MB 235.7, MB 235.74, and related specs)
- Toyota/Lexus Gear Oil LT/LX applications
- VW/Audi G 052 513
Valvoline Transfer Case Fluid
Valvoline Transfer Case Fluid is an aftermarket synthetic replacement formulated specifically for GM Auto-Trak II and Ford XL-12 applications.
This fluid is built with premium base stocks and additive technology designed for chain-driven transfer cases in full-size and compact trucks and SUVs. At 100°C, it measures 5.91 cSt, which is thinner than Auto-Trak II’s 7.3 cSt specification. This viscosity difference is notable but Valvoline markets this product explicitly for Auto-Trak II applications.
The Brookfield viscosity at -40°C is 10,200 cP, indicating solid cold-start performance. The fluid is red (not blue like OEM Auto-Trak II), so don’t be surprised if you see a color change after filling.
Valvoline formulates this fluid to provide low-temperature fluidity, wear protection through advanced additives, oxidation control for extended high-temperature operation, and seal compatibility. The viscosity index of 156 shows good stability across temperature ranges.
The product is recommended for transfer cases requiring Dexron/Mercon or ATF+4 fluids in addition to Auto-Trak II and XL-12 specifications.
Other compatible applications:
- Ford XL-12 transfer cases
- Transfer cases requiring Dexron/Mercon fluids
- Transfer cases requiring ATF+4
About GM 9986186
GM specification 9986186 is the official technical standard for Auto-Trak II Transfer Case Fluid. This specification defines the requirements for fluid used in automatic transfer cases like the NVG 246-NP8 or NP246. These are the transfer cases with an Auto setting that senses wheel slippage and engages internal clutches without driver input.
The current GM part number meeting this spec is 88900402, which supersedes the older 12378508. You’ll also see related part numbers like 10953626, 88865625, and 88865882 depending on packaging and distribution channels.
Fluid meeting 9986186 runs at approximately 7.3 cSt at 100°C. The spec requires special friction modifiers engineered to protect wet clutch packs inside the transfer case. Without these modifiers, clutches burn up and you’ll experience shudder, clunking, or grabbiness during low-speed turns in Auto 4WD mode.
The specification also mandates improved oxidation resistance for extended high-temperature operation. Transfer cases run hot, and the fluid chemistry needs to survive.
This strict adherence to chemistry is common across the GM lineup. For instance, manual transmission owners often face similar hurdles when searching for a GM 88861800 equivalent that won’t compromise synchronizer performance.
Why Auto-Trak II Alternatives are Hard to Find
Auto-Trak II is a proprietary “super secret fluid,” which makes its aftermarket equivalents extremely rare and hard to find. Its close-guarded formulation also gave rise to several unverified rumors online.
The most common rumor claims Auto-Trak II is just synthetic Dexron or Mercon with blue dye and extra friction modifier. Auto-Trak’s viscosity matches Dexron III exactly. However, chemical analysis shows Auto-Trak II contains specific additives (150 ppm Boron, 300 ppm Phosphorus) that standard ATF lacks.
Some may claim that Auto-Trak II is a repackaged Mobil 424 tractor hydraulic fluid. This rumor stems from similarities between GM and Jeep transfer case fluids (both use clutch packs and similar blue fluids). But there’s no verification for this claim.
If you’re not sure that it’s an Auto-Trak II equivalent (meets GM 9986186), don’t take that chance.
Closing Notes
Auto-Trak II contains friction modifiers for wet clutch packs that standard ATF doesn’t have. That’s what makes it different, not the blue dye.
If you use an aftermarket fluid, choose one that lists GM specification 9986186 compatibility. Valvoline Transfer Case Fluid and TRIAX DTF-2 both claim to meet this standard, though their viscosities differ from OEM.
Don’t mix different fluids. Change your transfer case fluid every 30,000 to 50,000 miles regardless of brand. Transfer cases run hot without dedicated cooling, so additives could break down faster than you might expect.
If your GMT-800 truck is under warranty, use ACDelco.
