Let's Get to Know the Fluids Used in Vehicles

You found a puddle of fluid under your car. You’re wondering: what is it? Could this leak point to a serious, even dangerous, problem?

Your car uses fluids to do all sorts of things, and these fluids occasionally leak out of the vehicle. Knowing what different fluids look like, feel like to the touch, and smell like can come in handy when you find a puddle of fluid in your garage and want to know what it means.

Engine Oil

Your car uses oils to lubricate metal parts so they can move against each other without friction. Oil can be made from petroleum or produced synthetically. Engine oil’s color varies by manufacturer and type.

Clean engine oil is usually skin-toned or light brown. Heavy gear oil is darker and as thick as honey. Used engine oil darkens with the residue left in the engine after fuel combustion. To the touch, oil is very slippery, and it smells of sulfur or burnt popcorn.

A car leaking oil will eventually break down, since the metal components will move while rubbing against each other.

what engine oil looks like, what color it is — Engine Oil

Oil leaks can be caused by failed engine or axle seals, a blockage in the engine’s ventilation, a loose oil filter or drain plug, or even oil spilled on the engine while topping it up.

If you find oil, try to find the source of the leak. If the leak is from the engine, check your oil level. If the level is fine and the leak is small, you can have the vehicle checked by a professional. If the leak is large, or if your engine’s oil has dropped significantly because of it, have the car towed to a mechanic.

Brake Fluid

Hydraulic fluid is used to operate the brakes, and sometimes power steering. Hydraulic fluid is designed to be compressed to generate high pressure to operate various devices.

Brake fluid is clear or light amber in color and has the consistency of water, but it’s slippery like oil. It smells similar to baby oil.

If you find brake fluid under your car, don’t drive it. Leaking brakes are dangerous. Have your car towed to a mechanic.

brake fluid - hydraulic fluid. what brake fluid looks like, what color it is — Brake fluid

Transmission Fluid

Transmission and transaxle fluids work both like oils and like hydraulic fluids. They lubricate metal parts and can be pressurized like hydraulic fluids to operate the transmission during gear shifts. In power steering systems, they’re sometimes used in place of hydraulic fluids.

Transmission fluids are usually dyed so they can be distinguished from other fluids. Most often they’re dyed red, but some manufacturers use other colors. The bright color is the easiest way to identify transmission fluids. They’re oily but generally thinner than oils, and have a burnt smell.

what transmission fluid looks like, its color — Transmission fluid

If you find transmission fluid, locate the leak and determine whether it’s caused by overfilling. A very small leak can be driven to a mechanic. If it’s a large leak, don’t drive the car.

Antifreeze

Antifreeze, or coolant, is mixed with water and is designed to remove heat from your engine. It also prevents the water in your cooling system from freezing and expanding in a way that could crack the metal and damage the engine.

Antifreeze is usually neon yellow or green. It has a very sweet smell. It feels slippery to the touch, like soapy water.

An antifreeze leak means a gasket has failed, or the engine has overheated and the coolant has been forced out of the system. Since hot coolant expands, the system builds pressure, so be careful when checking a hot engine for leaks — the coolant can scald you.

what color is antifreeze, what does it look like — Antifreeze can be yellow or green.

If coolant is coming out of the overflow tank, your engine is probably running too hot, and you need to have it checked by a mechanic. If it’s a very slow leak, check around the hoses and fittings for dripping. If you have a high-pressure leak flowing out of an area due to corrosion or a failed gasket, have your car towed to a mechanic.

Water

Water can drip from your car for many reasons, most of them harmless. Most often, dripping water comes from condensation off the air conditioner. Water can also condense in the exhaust system and get blown out of the tailpipes before the exhaust gets hot enough to evaporate it. Water can also collect in areas after washing or driving in wet conditions, and later drain out as it’s dislodged.

You should be concerned if your engine cooling system is leaking water, as it could mean there’s no antifreeze in the system. If water is coming from the transmission or another system, it means there’s a leak letting water in. This needs to be checked, since water can lead to rust.

Fuel

Today, the most common fuels are gasoline and diesel. Fuels have the consistency of water and can range from clear to amber in color depending on the fuel’s grade and refinement. Diesel fuel has a slightly oily feel.

Fuels are known for their strong smell, which is a good indicator of a fuel leak. Biofuels can smell like cooking oil or burnt popcorn, depending on what they’re made from.

what diesel fuel looks like, its color — Diesel

what gasoline looks like, its color — Gasoline

If you find a fuel leak that isn’t caused by overfilling the tank, don’t drive the car. Fuel leaks are very dangerous and potentially explosive. If you find a fuel leak on your car, call a mechanic.

Windshield Washer Fluid

Windshield washer fluid is usually blue, though some manufacturers use other colors to differentiate their products. Most of these fluids are good for de-icing down to a certain temperature, and some help remove stubborn residue from your windshield. Washer fluid has a water-like consistency and can have a mild cleaner or sweet smell.

Leaking washer fluid is nothing to panic about. While running the system dry for too long isn’t a great idea, your car will keep running even if it runs out. You can have the leak fixed whenever you like.