Why isn’t all lubricant oil the same in function?
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All lubricant oil *is* the same in function…to lubricate.
What’s different is the conditions under which it needs to do that, which drives you to different formulas (“recipes”) for different oils with the same basic function.
How hot & cold does it need to work? How long does it need to last? How much pressure will it be exposed to? What other chemicals or stuff might be mixed into it and how well does it have to work when that happens? Does it matter if it’s flammable? What other functions does it have to do, if any, beyond lubrication? How much can it cost? How much of it needs to be available, and how easy does it need to be to make? How bad is it if it breaks down?
The answers to all these questions between, say, a handheld power tool, a Formula 1 race car, a bulldozer, and a rocket are *wildly* different.
There is always friction between two lubricated surfaces, the lubricants job is designed to minimise that friction as much as possible, but it is always there.
How well a lubricant performs compared to others is determined by its properties and how they are influenced by external forces such as heat, pressure, moisture, mating surfaces etc.
This is why an engine oil designed for warmer climates can result in engine failure when used in cold climates and vice versa.
Because they operate under different conditions and have different requirements. The engine oil in your car has to work in relatively high temperatures and supports the crankshaft allowing it to ride on a thin layer of oil to prevent metal to metal contact. It also has to deal with the byproducts of combustion that sneaks past the piston rings and keep the engine clean. Since it goes into an engine and some will likely get burnt; the byproducts of it’s combustion can’t clog catalytic converters. Gear oil, on the other hand, works in the differentials and manual transmissions. It’s designed to be in the car for 30k+ miles at much lower temperatures and doesn’t get burnt inside the engine so it can have additives in there to deal with the extreme pressure it will likely see between the gears of a car. It also might need friction modifiers required by limited slip differentials and special parts of the transmission that require friction to work. Grease is designed to displace water and keep it from coming in as well as stay in place for years unlike oils.
Just a few examples off the top of my head:
**Viscosity** – some are thick like honey, some are thin like water
**Viscosity modifiers** – For a car – it’s actually ideal if it’s more watery when the engine is cold so when you start the engine the oil splashes around and coats everything. Then as the engine warms up the oil thickens to offer better protection. Most oils work the opposite way where they’re thicker when cold, and thin when warm.
**Safety** – If you have a personal lubricant that’s designed for humans – for example when giving a baby a rectal thermometer – then you have to make sure it’s safe. If it’s for a car engine, toxicity is a bit less important.
**Taste** – If a doctor uses a lot of personal lubricant on their patients, if it has a bad taste then maybe that taste will stay on their hands and ruin the taste of the sandwich they have for lunch. As a result some adults like flavored lubricants that are tasty. If they have a sandwich with peanut butter and grape jelly, maybe they’ll choose a grape flavored lubricant to compliment his sandwich.
**Oil vs water based** – oil based lubricants can damage certain plastics, but they last longer. Water based lubricants are safer on plastic, but can dry up faster.
**Solvent vs silicone** – solvent based lubricants like WD-40 dry up quickly so they’re designed for permanent use. Silicone lubricants can last a long time on the other hand.
**Corrosion Inhibitors** – some lubricants contain ingredients to stop metals from rusting. A lubricant that protects iron can be different than one that protects aluminum. If it’s for plastic, maybe these corrosion inhibitors will do more harm than good.
**Planned Service Life** – if you have an engine and you change the oil every 5,000 miles – you design a lubricant that offers the best protection for 5,000 miles. If you have a transmission and you change it every 50,000 miles – now you need longer lasting substances.
**Environmental Friendliness** – Transmission oil used to be made of whales, and it was super effective. But killing whales wasn’t good for the environment. When they stopped putting whales in transmission oil, then transmissions started breaking way more frequently – [https://www.nytimes.com/1975/04/17/archives/transmission-problems-in-cars-linked-to-ban-on-whale-killing.html](https://www.nytimes.com/1975/04/17/archives/transmission-problems-in-cars-linked-to-ban-on-whale-killing.html#:~:text=DETROIT%2C%20April%2016%E2%80%94Owners%20of,in%20its%20automatic%20transmission%20fluid)
**Ambient Conditions** – If something is completely sealed, it’s not exposed to any air. If something is exposed to air, then it needs to be more resistant to oxidation. If something gets very hot like a turbocharger, then it needs to be more resistant to heat. In a very cold place like Antarctica, it needs to be resistant to cold. Even in a car – the sulfur content of fuel can change the type of oil needed.
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