Motor Oil vs Gear Oil: Which One Should You Buy?

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Below: how the fluids differ, what each one does, and motor oils ranked for engine work.

Motor oil vs gear oil: where the difference comes from

Motor oil works inside an engine, where pistons, bearings and valves move at speed and combustion leaves deposits behind. The motor oil listings in this group stress wear protection, deposit defense, sludge control and heat protection, which are engine problems, not gear problems. A motor oil grade, such as 0W-20 or 5W-20, is named on the listing, and the vehicle manual names the grade for that engine.

Gear oil works on gear teeth, where the load is concentrated on a small contact area as gears mesh. Its job is to keep those teeth separated and protected under that load, in a gearbox, a differential or a transfer case. That is a different job from engine lubrication, so a fluid made for an engine should not be poured into a gear set, and a fluid made for a gear set should not be poured into an engine, unless the manual for that vehicle calls for it.

Gear that fits the job

No gear oil listing is included in this group, so the gear section below covers motor oils only, ranked by their stated protection claims. Gear oil choice should follow the vehicle manual and the gear set requirements, not a motor oil listing.

Ranked first is the Valvoline Advanced Full Synthetic SAE 0W-20 Motor Oil, in a 5 QT size. The listing states 40% stronger wear protection than industry standards, 15% better deposit defense versus industry standards, and up to 2.5X better heat protection versus industry standards. It also states advanced protection against wear, friction, heat and deposits, excellent low-temperature flow for cold starts, and requirements met including ILSAC GF-7A, API SQ, API SP, and API SN with SN PLUS. Additional specifications named are Ford WSS-M2C962-A1, Chrysler MS-13340, and GM dexos 1 Gen 3. It ranks first on the breadth of its stated protection claims.

Ranked second is the Mobil 1 Advanced Fuel Economy Full Synthetic Motor Oil 0W-20, in a 5 Quart size. The listing states that it helps increase engine efficiency, contains additives to help fight sludge, and is suitable for hybrid vehicles. The title states 10,000-Mile Protection, while the bullets state that it protects for 15,000 miles, so the two figures do not agree, and the bullet figure is used here with that discrepancy noted. The spec table states a Limited Warranty, with a note to contact the manufacturer for full details, without a stated term length.

Ranked third is the Mobil 1 High Mileage Full Synthetic Motor Oil 0W-20, in a 5 Quart size. The listing states high mileage for engines with 75,000+ miles, protection for 15,000 miles, a seal conditioner, and sludge prevention. It also states that it helps extend engine life of higher mileage vehicles and keeps an engine running like new. The spec table states a Limited Warranty, with a note to contact the manufacturer for full details, without a stated term length. It ranks below the Advanced Fuel Economy pick because its stated focus is higher mileage engines rather than the broadest protection claims.

Ranked fourth is the Valvoline MaxLife High Mileage 5W-20 Synthetic Blend Motor Oil, in a 5 Quart size. The listing states formulation for engines with 75,000 miles or more, seal conditioners to help prevent oil leaks and reduce oil consumption, 20% better wear protection and 15% better sludge defense than industry standards, and extra detergents against friction, corrosion and deposits. It meets or exceeds requirements including ILSAC GF-7A, API SQ, API SP, and API SN with SN PLUS, with additional specifications Ford WSS-M2C970-A-1 and Chrysler MS-13340. It ranks last here on the breadth of its stated protection claims in this set, with a high-mileage focus rather than the broadest protection claims.

When to use which fluid

Use motor oil for an engine oil change, in the grade the manual names, and use gear oil for a manual gearbox, differential or transfer case service, in the fluid the manual names for that gear set. Do not swap the two because both come in a jug and both feel oily; the jobs, the parts and the protection claims are different. If the manual names a motor oil grade, pick a motor oil listing with that grade, such as 0W-20 or 5W-20 in this group, and check the stated protection claims against the engine in hand. If the job is a gear set, look for a gear oil listing made for that gear set, since none of the listings in this group is a gear oil.

Follow each maker’s instructions for handling and changing fluids, and collect used oil for recycling. Check the level and the condition of the fluid during routine garage work, and change it on the schedule the vehicle manual gives, rather than waiting for a problem to show up.

FAQ: garage tools

Can motor oil be used as gear oil?

No, not as a general swap. Motor oil is made for engines, with claims for wear, deposits, sludge and heat inside an engine. Gear oil is made for gear sets, manual gearboxes, differentials and transfer cases, where gears mesh under load. Use the fluid the manual names for each part.

Why do the Mobil listings give different mile figures?

The Mobil 1 Advanced Fuel Economy title states 10,000-Mile Protection, while its bullets state protection for 15,000 miles. The Mobil 1 High Mileage listing states protection for 15,000 miles in its bullets, without that title discrepancy. Check the listing in hand, since the two figures on the Advanced Fuel Economy listing do not agree.

Which grade should I use, 0W-20 or 5W-20?

Use the grade the vehicle manual names. The listings in this group include 0W-20 full synthetic motor oils from Mobil and Valvoline, and a 5W-20 synthetic blend from Valvoline. Grade alone does not decide quality; the stated wear, deposit and heat claims, and the specifications met, also matter.

Do high mileage oils fit older engines?

The high mileage listings in this group state engines with 75,000 miles or more, or 75,000+ miles. Valvoline MaxLife states seal conditioners to help prevent oil leaks and reduce oil consumption, and Mobil 1 High Mileage states a seal conditioner and sludge prevention. For a lower mileage engine, the Valvoline Advanced listing in this group states broader protection claims.

Is there a gear oil pick in this group?

No, all four listings in this group are motor oils. For a gear set service, look for a gear oil listing made for that gear set, such as the best heavy duty gear oil guide, and follow the manual for the fluid required.

Related: synthetic vs conventional motor oil, and the engine and shop equipment hub.