Gear oil

Gear oil is the heavy-duty lubricant designed for gearboxes, differentials, and transfer cases — basically, anywhere metal teeth are chewing against each other under high load.

Here’s the straight business rundown:

1. Core Function
    •    Lubrication: Creates a protective film between gear teeth to prevent metal-to-metal contact.
    •    Load handling: Withstands extreme pressure (EP) and shock loads without breaking down.
    •    Cooling: Carries heat away from friction zones.
    •    Protection: Fights rust, corrosion, and oxidation.

2. Viscosity & Classification
    •    Gear oils are graded under SAE J306 (not to be confused with SAE engine oil grades).
    •    Common grades: 75W-90, 80W-90, 85W-140.
    •    “W” = winter rating (low-temp flow), the second number = high-temp viscosity.

3. API GL Ratings (match to application, or you’ll destroy the gearbox)
    •    GL-1 to GL-3: Light duty, obsolete for most modern gearboxes.
    •    GL-4: Moderate EP — used in manual transmissions with brass/bronze synchros (won’t attack yellow metals).
    •    GL-5: High EP for hypoid differentials; higher sulfur-phosphorus content (can corrode synchros if used in wrong application).
    •    MT-1: Heavy-duty non-synchro manual transmissions.

4. Base Types
    •    Mineral gear oils: Lower cost, good for standard drain intervals.
    •    Synthetic gear oils: Better high/low temp performance, longer service life, better oxidation stability.
    •    Semi-synthetic: Balanced cost vs performance.

5. Additive Packages
    •    EP additives: Sulfur-phosphorus chemistry for load protection.
    •    Anti-foaming agents
    •    Corrosion inhibitors
    •    Viscosity improvers

6. Common Failure Causes
    •    Wrong API rating (GL-5 in a GL-4 spec transmission can kill synchros).
    •    Overheating due to underfill or wrong viscosity.
    •    Water ingress (milkshake-looking oil = scrap it).
    •    Contamination from metal wear particles.

7. Service Life
    •    Light-duty cars: 50,000–100,000 km.
    •    Heavy trucks/off-road: change based on hours of service or oil analysis, sometimes yearly.

CVT stands for Continuously Variable Transmission — it’s a type of gearbox that doesn’t have fixed gear ratios like a manual or conventional automatic.

Here’s the blunt version:

1. How it Works
    •    Uses a belt and pulley system (or sometimes a chain) where the pulleys change diameter on the fly.
    •    This lets the transmission continuously adjust the gear ratio to keep the engine in its most efficient RPM range.
    •    No gear “steps” — acceleration feels smooth, almost like a scooter or snowmobile.

2. Advantages
    •    Fuel efficiency: Keeps engine at optimal RPM for load.
    •    Smooth drive: No shift shock.
    •    Better torque control: Especially in low-speed climbing or towing (if designed for it).

3. Downsides
    •    Driving feel: Lacks the “kick” of gear changes; some drivers hate it.
    •    Durability: Early CVTs had belt wear and overheating issues, especially in high-torque applications.
    •    Cost: Repairs are pricey; often cheaper to replace the unit than rebuild.

4. Where You’ll See Them
    •    Many Japanese brands (Toyota, Nissan, Subaru, Honda) in sedans and crossovers.
    •    Hybrid cars (Prius, etc.) often use e-CVTs (planetary gear-based, not belt-driven).
    •    Powersports (ATVs, snowmobiles).

5. Key Maintenance Point
    •    Despite “lifetime fluid” marketing, CVT fluid must be changed (often every 40–60k km) to prevent belt/pulley wear and keep hydraulic pressure stable. Wrong fluid kills them fast.