The fastest way to turn a healthy transmission into a warranty claim is to put the wrong fluid in it. Eaton and Allison — the two brands under most heavy trucks in North America — do not share a fluid, and within each brand the correct spec depends on the model, the vocation, and even the year. Allison automatics want a TES-approved fluid; Eaton manuals and automated manuals want PS-386; and using a generic ATF or the wrong grade can cause shift problems within 10,000 miles and void the OEM warranty outright. This guide lays out the actual fluid specs for each brand — TES 295, TES 668, PS-386 — the real service intervals for general versus severe duty, why fluid analysis beats guessing, and how PM software keeps every different spec and interval straight across a mixed fleet so nothing gets the wrong fluid or a missed service. Start a free trial or book a demo to see transmission PM scheduling built for a mixed Eaton and Allison fleet.
PREVENTIVE MAINTENANCE · VEHICLE FLUIDS
Eaton & Allison Transmission Fluid Service: A Fleet PM Guide
Two brands, different fluids, different intervals — and a wrong-fluid mistake that voids the warranty. Get the exact spec for each transmission, the real general and severe-duty intervals, and let PM software keep every spec straight across the fleet.
The Warranty-Voiding Mistake
Generic ATF like DEXRON-VI is no longer approved in commercial on-highway Allison transmissions, and using a non-approved fluid can cause shift problems within 10,000 miles and void the transmission warranty. Eaton is just as strict: since January 1, 2017, warranty coverage requires a PS-386 approved lubricant. The fluid on the shelf that "looks close enough" is how a five-figure transmission becomes an out-of-pocket repair.
Eaton vs. Allison: The Fluid Split
These are two fundamentally different transmission families with different fluids. The first rule is knowing which brand — and which spec — each truck in your fleet actually takes.
EATON
Manual & Automated Manual
Required fluid: PS-386
Applies toEndurant HD/XD, UltraShift PLUS, Fuller Advantage, FR & RT Series
Fluid typeFull synthetic, non-EP
Linehaul interval~500,000 miles
Vocational interval~120,000 miles
Special caseProcision dual-clutch uses PS-278 only
PS-386 replaced the older PS-164 rev7 and is mandatory for warranty since 2017. The differential still runs 75W90 EP-5 gear lube — never put EP gear oil in the transmission.
ALLISON
Automatic
Required fluid: TES 295 / TES 668
Applies to1000, 2000, 3000 & 4000 Series automatics
Fluid typeFull synthetic ATF (TranSynd & approved)
General duty~50,000 miles
Severe duty25,000 mi / 2,000 hrs
Best practiceFluid analysis every ~12,500 mi
TES 668 is the newest spec and supersedes TES 295 — it's backward-compatible and keeps the same drain intervals. TES 389 is older and gives shorter intervals. High-capacity filters extend service life.
Decoding the TES and PS Spec Numbers
The alphabet soup of transmission fluid specs isn't marketing — each code is a specific OEM approval, and mixing them up is how the wrong fluid ends up in a transmission.
TES 668
Allison's newest fluid specification, superseding TES 295. Full synthetic with better oxidation stability and wear protection; backward-compatible with 295/389/468 and keeps the same drain intervals. The direction Allison is moving all fleets.
TES 295
The long-standing synthetic Allison spec required for 3000/4000 series and for Extended Coverage. Enables the long drain intervals. Still fully valid and widely stocked while fleets transition to 668.
TES 389
An older, conventional Allison fluid. Usable in some traditional on-highway units but does not deliver the extended drain or filter intervals of TES 295 — the cheaper fluid that costs more in service frequency.
PS-386
Eaton's synthetic spec for manual and automated transmissions, required for warranty since 2017. Non-EP, reduces sump temperatures, and supports the long linehaul drain intervals. Replaced the obsolete PS-164 rev7.
PS-278
The only approved lubricant for the Eaton Procision dual-clutch transmission. Do not use it in other Eaton models, and don't substitute PS-386 in a Procision — this is a common cross-up.
Not Approved
DEXRON-VI and C4 fluids are no longer recommended in commercial on-highway transmissions. Generic ATF may cause shift problems within 10,000 miles and voids the OEM warranty. "Universal" is not a spec.
Service Intervals by Brand & Duty Cycle
The single biggest interval mistake fleets make is running a severe-duty truck on the general-duty schedule. Duty cycle changes everything. Swipe the table horizontally on mobile.
← Swipe to see all columns →
| Transmission | Fluid | General / Linehaul | Severe / Vocational |
|---|---|---|---|
| Allison 3000/4000 | TES 295 / 668 | ~50,000 mi | 25,000 mi or 2,000 hrs |
| Allison 1000/2000 | TES 295 / 668 | Per Allison schedule | Shorter, per vocation |
| Eaton Fuller / FR / RT | PS-386 | ~500,000 mi (linehaul) | ~120,000 mi (vocational) |
| Eaton Endurant | PS-386 | Per Eaton schedule | To 2,000 hrs / 5 years |
| Eaton Procision | PS-278 only | Per Eaton schedule | Per Eaton schedule |
| Severe-duty triggers | Any | — | Refuse, transit, on/off-highway, >1 stop per mile, retarder |
i
Change the fluid AND the filters, on whichever comes first: Allison's rule is to change fluid and filters at or before the recommended mileage, months, or engine hours — whichever elapses first. A truck with a dense stop-and-go duty cycle often hits the hour limit long before the mileage limit, so tracking by miles alone quietly overshoots the real interval. This is exactly why Allison recommends fluid analysis as the primary method for setting intervals, not the odometer. See multi-trigger interval tracking in action.
4×
faster fluid degradation at 240°F versus normal
Heat Is What Actually Ages the Fluid
Transmission fluid life is governed by temperature as much as mileage. As a rule of thumb, every 20°F above 200°F roughly halves fluid life — so a transmission running at 240°F is destroying its fluid about four times faster than one at 200°F. Overheating usually traces to low fluid level, clogged cooler lines, a failed cooler fan, an overloaded route, or excessive idle in heat. Catching a temperature trend early is what turns a fluid change into a save instead of a rebuild.
One fleet, five different fluid specs and intervals — spreadsheets can't hold that.
Fleet Rabbit stores the exact fluid spec on each transmission and schedules its service by miles, hours, and time — so no Allison runs on Eaton's interval and no truck ever gets the wrong fluid.
Why Transmission PM Is a Multi-Spec Tracking Problem
A mixed fleet might run three Allison series and four Eaton models, each with its own fluid, interval, and duty classification. The chemistry is knowable; keeping it all straight across dozens of trucks is where it breaks down — and where PM software pays for itself.
Fluid Spec on Every Asset
Each transmission's exact fluid — PS-386, TES 668, PS-278 — lives on its record, so the tech doing the service sees precisely what to use and the wrong-fluid warranty risk disappears.
Multi-Trigger Scheduling
Service triggers on whichever comes first — miles, engine hours, or months — so a dense-cycle truck that hits its hour limit early gets serviced on time instead of at the mileage overshoot.
Duty-Cycle Aware Intervals
Flag a vehicle as severe duty and it gets the shorter interval automatically — no more running a refuse or transit truck on the linehaul schedule and wearing it out early.
Fluid Analysis & History Logs
Record oil-analysis results and every service into one history, so you can follow Allison's advice to set intervals by fluid condition and prove the maintenance for warranty and resale.
Keep Every Transmission on Its Own Correct Schedule
Fleet Rabbit stores the exact fluid spec for every Eaton and Allison transmission, schedules service by miles, hours, and months on whichever comes first, applies severe-duty intervals automatically, and logs fluid analysis into a full history — so no truck gets the wrong fluid and no service slips. At $5/vehicle/month, no hardware, live within 72 hours, free for up to three vehicles.
Fluid spec per transmission
Miles / hours / months triggers
Severe-duty aware
Fluid analysis logs
Transmission Service Do's & Don'ts
The rules that keep a transmission — and its warranty — intact, in one place for the shop. Swipe the table horizontally on mobile.
← Swipe to see all columns →
| Topic | Do | Don't |
|---|---|---|
| Fluid choice | Use the exact OEM-approved spec per model | Use "universal" ATF or DEXRON-VI |
| Filters | Change filters with the fluid, every interval | Change fluid but reuse old filters |
| Interval basis | Track miles, hours, and months together | Rely on odometer alone |
| Duty cycle | Apply severe-duty intervals when they fit | Run vocational trucks on linehaul intervals |
| Eaton diff | Keep 75W90 EP-5 in the differential | Put EP gear oil in the transmission |
| Overheating | Investigate coolers, fans, fluid level | Ignore a rising transmission temp |
Frequently Asked Questions
Can I use the same fluid in Eaton and Allison transmissions?
No. Eaton manual and automated transmissions require a PS-386 approved synthetic, while Allison automatics require a TES-approved automatic transmission fluid such as TES 295 or the newer TES 668 — they are different fluids for fundamentally different transmission designs. Using the wrong one risks shift problems and a voided warranty. On a mixed fleet the safest approach is to store each transmission's exact spec on its record so no truck gets the wrong fluid, which is something you can book a demo to see set up across your whole roster.
What's the difference between TES 295 and TES 668?
TES 668 is Allison's newest fluid specification and it supersedes the long-standing TES 295. It's a full synthetic with better oxidation stability and wear protection, it's backward-compatible with TES 295, 389, and 468, and importantly it keeps the same drain intervals — so switching is straightforward. Allison isn't forcing an immediate change but is steering fleets toward 668 over time. Understanding which of your Allison units are on which spec, and tracking that transition, is something you can book a demo to manage on each asset record.
How often should I change Allison transmission fluid?
It depends heavily on duty cycle. General on-highway service with an approved TES 295 or 668 fluid and high-capacity filters runs around 50,000 miles, but severe duty — refuse, transit, on/off-highway, or more than one stop per mile — drops to roughly 25,000 miles or 2,000 hours, whichever comes first. Allison actually recommends fluid analysis every 12,500 miles or so as the primary way to set the interval rather than a fixed number. Tracking those multiple triggers per vehicle is exactly what you can book a demo to automate.
How often should I change Eaton transmission fluid?
For Eaton Fuller, FR, and RT series running PS-386 synthetic, linehaul applications typically go about 500,000 miles between services, while vocational applications run closer to 120,000 miles because of the harder duty cycle. Endurant models follow their own schedule, often expressed to 2,000 hours or five years. The wide spread is exactly why the vocation classification matters so much, and applying the right interval to each truck automatically is something you can book a demo to see handled by duty cycle.
Does using non-approved fluid really void the warranty?
Yes. Allison no longer recommends DEXRON-VI or C4 fluids in commercial on-highway transmissions, and generic ATF can cause shift problems within about 10,000 miles while voiding the OEM warranty. Eaton has required PS-386 approved lubricant for warranty coverage since January 1, 2017. Beyond the warranty issue, the wrong fluid genuinely damages seals, clutches, and friction materials. Keeping the approved spec visible to every technician is the simplest protection, and it's something you can book a demo to build into your service workflow.
Do I change the filters every time I change the fluid?
Yes — for Allison, the rule is to change fluid and filters together at or before the recommended interval, and high-capacity filters are what enable the extended drain intervals in the first place. Reusing an old filter with fresh fluid undercuts the whole service and can shorten the fluid's effective life. Scheduling the filter change as part of the same PM event, with the right filter part number on the record, is something you can book a demo to see bundled automatically so it never gets skipped.
Why does transmission temperature matter for fluid life?
Because heat ages fluid faster than miles do. As a rule of thumb, every 20°F above 200°F roughly halves the fluid's life, so a transmission running at 240°F degrades its fluid about four times faster than one at 200°F. Persistent high temperatures usually point to low fluid, clogged cooler lines, a failed cooler fan, an overloaded route, or heavy idle time. Watching for a temperature trend and acting on it can save a transmission, and building that awareness into your maintenance triggers is something you can book a demo to explore.
How does PM software help with mixed Eaton and Allison fleets?
By holding every transmission's spec and schedule in one place instead of a technician's memory or a spreadsheet. It stores the exact fluid — PS-386, TES 668, PS-278 — on each asset, schedules service on whichever of miles, hours, or months comes first, applies severe-duty intervals to the trucks that need them, and logs fluid analysis into a full history for warranty and resale. Across a fleet with several transmission families that's the difference between every truck on its correct schedule and a warranty-voiding mistake, and seeing it run on your own equipment is exactly what you can book a demo to do.
Never Put the Wrong Fluid — or Miss a Service — Again
Fleet Rabbit keeps every Eaton and Allison transmission on its own correct schedule — the exact fluid spec on each asset, service triggered by miles, hours, and months, severe-duty intervals applied automatically, and fluid analysis logged for warranty. Protect the most expensive driveline component on every truck. Integrated in 5–7 working days, at $5/vehicle/month, free for up to three vehicles, with no hardware required.
Free tier for up to 3 vehicles · No credit card required · No hardware installation
August 3, 2026By Emily Parker
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