Allison Transmission Fluid Changes: TES 295 and TES 668 Explained

Allison Transmission updated its automatic transmission fluid spec from TES 295 to TES 668 back in 2020, swapping a mineral base oil for a full synthetic fluid that holds up better under heat and lasts longer between services. If your truck, bus or off-road machine runs an Allison 1000, 2000, 3000 or 4000 series transmission, it pays to know the difference before your next Allison transmission fluid change, because the wrong fluid can affect your warranty and how your clutches perform.

Short version: TES 668 fluid is backward compatible with anything approved for TES 295, Heavy Automatics stocks Valvoline branded TES 668 fluid and can talk you through exactly what your series and duty cycle needs.

Fluid does more than lubricate in an Allison automatic. It also carries the hydraulic pressure that applies the clutches. Fluid that breaks down under heat or oxidises early means slipping, harsher shifts and, eventually, clutch wear that turns into an expensive repair instead of a routine service.

TES 295 vs TES 668: What Changed

TES 295 was Allison's long standing fluid spec, built on mineral base oils, and it did the job for years. TES 668 arrived in 2020 with a full synthetic base and a stronger additive package. That gives it better resistance to oxidation, less sludge and varnish build-up, smoother shifts across a wider temperature range and less clutch shudder as the fluid ages, while holding the same or longer drain intervals.

Allison's own approved fluids page confirms TES 668 is the current recommendation for the 1000, 2000, 3000 and 4000 series and now suggests anyone still running TES 295 or TES 468 make the switch at their next service.

Can You Run TES 668 Fluid in a Transmission That Calls for TES 295?

Yes. TES 668 is backward compatible with equipment approved for TES 295, TES 389 or TES 468, so upgrading at your next service does not need any hardware changes. Staying on a TES 295 product is fine too, if that is what your fleet already runs and it is still available, though most workshops, Heavy Automatics included, are moving new stock over to TES 668 as the older fluid gets phased out.

Which Allison Transmissions Take TES 668 Fluid

TES 668 fluid suits Allison's 1000, 2000, 3000 and 4000 series transmissions, which cover most trucks, buses and emergency vehicles on Australian roads, Heavy Automatics can confirm the right fluid and pack size for your transmission and duty cycle before you book a service.

When to Change Your Allison Transmission Fluid

Allison sets fluid and filter change intervals by series, duty cycle and Prognostics oil-life monitoring status, so there is no single number that fits every vehicle. Heavy Automatics checks your transmission's own service schedule and Prognostics data where it is fitted, then confirms when your next Allison transmission fluid change is due.

A few signs are worth a check between scheduled services:

• Shifts feel harsher or slower to engage than usual, particularly when the transmission is cold.
• The fluid looks darker than normal or smells burnt on the dipstick or through a sample.
• Your Prognostics system or dashboard raises a service reminder.
• You are approaching the distance, hours or months interval Allison sets for your series and duty cycle.

Why Get Your Allison Transmission Fluid Changed at Heavy Automatics

Heavy Automatics is the largest Authorised Distributor of Allison Transmissions in Australia, family owned since 1990 and an Allison distributor since 2008. Allison has recognised the business with its Gold Standard for Performance Award repeatedly since 2014 and a 15 Years of Excellence Award in 2024. Five service facilities across the mainland capital cities and more than $10 million in parts inventory mean Heavy Automatics carries the fluid your transmission needs and technicians trained to fit it right, whatever series you run.

That scale matters because the wrong pack size, the wrong additive package or a fluid without genuine Allison approval is how a routine service turns into a warranty dispute later. Heavy Automatics works to Allison's own specifications rather than a generic aftermarket substitute.

Book Your Allison Transmission Fluid Change

Call Heavy Automatics on 1800 022 831 to book a fluid change, or shop Allison-approved transmission oil directly through the Heavys store. For the full range of transmissions and service options covered, visit the Allison Transmissions page.

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