AMSOIL guide
80W-90 Gear Oil Guide
80W-90 is the traditional warm-climate viscosity grade for hypoid differentials, transfer cases, and other GL-5 final-drive applications. AMSOIL SEVERE GEAR 80W-90 100% Synthetic Gear Lube (AGL) is the severe-duty pick: full synthetic, API GL-5, engineered for the towing, hauling, and off-road temperatures that overwhelm a conventional 80W-90. For cold-climate operation or sustained extreme load, step to 75W-90 (better cold-flow) or 75W-140 (heavier high-temp grade). Always honor the GL-4 vs GL-5 rule: GL-4 in manual gearboxes with brass synchros, GL-5 in differentials.
Shop AMSOIL SEVERE GEAR 80W-90
AMSOIL SEVERE GEAR viscosity options at a glance
| Viscosity | Best fit | Where to buy |
|---|---|---|
| SEVERE GEAR 75W-85 | Cold-climate light-duty differentials | Buy online | Product details |
| SEVERE GEAR 75W-90 (SVG) | Most modern light-truck and SUV differentials, cold-climate towing | Buy online | Product details |
| SEVERE GEAR 80W-90 (AGL) | Warm-climate differentials, traditional muscle car and classic truck | Buy online | Product details |
| SEVERE GEAR 75W-110 | Heavy-duty pickup and SUV differentials, hot-climate towing | Buy online | Product details |
| SEVERE GEAR 75W-140 | Severe-duty 3/4-ton and 1-ton truck differentials | Buy online | Product details |
The GL-4 vs GL-5 rule
Gear oil is governed by the API gear-oil service categories. GL-4 uses a moderated sulfur-phosphorus EP additive package designed to protect gears without corroding the brass and bronze synchros found in most manual transmissions. GL-5 uses a higher-EP additive package designed for the heavy gear shock found in hypoid differentials and final drives.
The rule is simple: GL-4 in the manual transmission, GL-5 in the differential. Putting GL-5 in a manual gearbox that calls for GL-4 corrodes the synchros and ruins shift feel within a few thousand miles. The matching manual transmission fluid guide covers the GL-4 side for synchromesh boxes and European 75W-90 GL-4 transaxles.
When to pick 80W-90 vs 75W-90 vs 75W-140
80W-90 (AGL) is the traditional warm-climate viscosity for hypoid differentials. It works well in muscle car, classic truck, and warm-climate light-truck applications where cold-flow is not the limiting factor.
75W-90 (SVG) has the same hot-temperature grade as 80W-90 with substantially better cold-flow at startup. Pick 75W-90 for cold-climate operation, for towing applications where the diff sees cold soak overnight before a hard morning pull, and for any modern light-truck or SUV that calls for 75W-90. The full breakdown lives in the 75W-90 gear oil guide.
75W-110 (SVT) and 75W-140 (SVO) are the heavier-duty picks for sustained towing, hauling, and 3/4-ton and 1-ton truck differentials that see continuous high-load operation.
Bottom line: when should you use 80W-90?
- Warm-climate hypoid differential, classic truck, muscle car. Pick AMSOIL SEVERE GEAR 80W-90 (also online from AMSOIL).
- Cold-climate or modern light-truck/SUV. Pick AMSOIL SEVERE GEAR 75W-90; see the 75W-90 gear oil guide.
- Hot-climate severe-duty towing. Pick AMSOIL SEVERE GEAR 75W-140.
- Manual transmission with brass synchros. Use a GL-4 fluid; see the manual transmission fluid guide.
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80W-90 gear oil FAQ
What is API GL-5?
API GL-5 is the gear-oil service category for hypoid differentials, transfer cases, and other final-drive applications that take heavy gear shock. The GL-5 additive package contains higher levels of sulfur-phosphorus EP additives than GL-4. Use GL-5 only in differentials and transfer cases. Putting GL-5 in a manual transmission with brass synchros corrodes the synchros.
When should I use 80W-90 vs 75W-90?
80W-90 is the traditional warm-climate viscosity for hypoid differentials. 75W-90 has the same hot-temperature grade with better cold-flow at startup, which matters for cold-climate operation and for towing applications where the diff sees cold soak overnight before a hard morning pull. AMSOIL builds SEVERE GEAR 80W-90 and SEVERE GEAR 75W-90. For severe-duty 75W-140 picks, see the 75W-90 gear oil guide.
Does AMSOIL SEVERE GEAR work in a limited-slip differential?
Yes. AMSOIL SEVERE GEAR contains friction modifiers compatible with most limited-slip clutch packs. For LSDs that specifically call for an additional friction modifier, AMSOIL Slip Lock Friction Modifier is the matched additive. Verify your differential's requirements against the OEM service manual.
How often should I change differential gear oil?
Most owners' manuals call for a change every 30,000 to 60,000 miles in normal service, with a shorter interval for severe service (towing, hauling, plowing, off-road). Sealed differentials still benefit from periodic drain and fill at the same intervals.
Is 80W-90 gear oil compatible across brands?
Yes for mineral 80W-90 gear oils. Synthetic and mineral 80W-90 gear oils are miscible, so a top-off with one in the other is safe. For best results, run a complete drain and refill with one oil rather than topping off across formulations long-term.
Where do I buy AMSOIL 80W-90 gear oil?
Order online from AMSOIL on the SEVERE GEAR 80W-90 product page, or browse the full gear oil lineup on AMSOIL's gear oil page. The matching gear lubricants overview covers AMSOIL's full SEVERE GEAR lineup with side-by-side spec comparisons.
Order AMSOIL SEVERE GEAR 80W-90
Order online from AMSOIL's SEVERE GEAR 80W-90 product page. To unlock up to 25% off, add an AMSOIL Preferred Customer membership to the same cart and qualifying products switch to member pricing immediately, with no separate sign-up step.