Car leaking oil: how serious is it

Reading the puddle before you panic

Slide a sheet of cardboard under the car overnight. It catches the drip, holds the colour, and shows you where under the car it is landing, which is most of the diagnosis.

The one warning light that means stop

Worth separating this from everything else on the page, because the two get confused constantly.

The oil pressure warning light, usually a red oil can symbol, does not mean the oil is low. It means the engine has lost oil pressure, and an engine running without pressure destroys its bearings in a very short time, sometimes within a minute. If that light comes on while driving, pull over, switch the engine off, and do not restart it to move somewhere more convenient.

The oil level warning, which on cars that have one is usually amber and often shaped differently, means the level has dropped below a mark. That is a top-up-and-investigate situation rather than an emergency.

Some cars only have the red pressure light and use it for both, which is why checking the dipstick before restarting is worth the two minutes. If the dipstick shows oil at a normal level and the red light was on, the pressure loss is mechanical and the engine should not be run.

We say this on every call about a red oil light: the cost of a tow or a mobile visit is a very small fraction of the cost of an engine, and the difference between those two outcomes is often a single drive.

Finding out whether it is actually oil

Cars carry six or seven different fluids and most of them can leak, so identifying which one is on the ground narrows the job immediately.

Engine oil is amber when fresh, darkening to brown and then black with age, and it feels slippery between the fingers. Transmission fluid and power steering fluid are both usually red or pink, slippery, and thinner. Coolant is brightly coloured, green, orange or pink depending on the type, smells distinctly sweet, and feels slightly sticky rather than oily. Brake fluid is clear to light brown, feels slippery, and is the one to take most seriously because a brake system leak affects stopping.

Then there is the fluid that is not a fault at all: clear water dripping under the passenger side after using air conditioning is condensate off the evaporator, and it is supposed to do that. Every summer somebody worries about it.

Location helps as much as colour. A drip under the front centre of the engine is a different set of suspects from one at the rear of the engine or at the very back of the car. Cardboard under the car overnight gives you both pieces of information at once and costs nothing.

Where engine oil usually leaks from

Valve cover gaskets are the most common, particularly on engines past 80,000 miles. The gasket sits at the top of the engine, hardens with heat over time, and starts to weep. Oil then runs down the outside of the engine and often drips onto the exhaust manifold on its way, which produces a burning smell and sometimes a wisp of smoke from under the hood. It is one of the more approachable repairs.

The oil pan gasket, at the bottom of the engine, is next. Oil pans also get damaged directly by road debris and by contact with speed bumps and kerbs, and a dented pan or a stripped drain plug leaks steadily.

The drain plug and the oil filter deserve a mention on their own, because a leak that started right after an oil change is usually one of those two: a plug not torqued correctly, a crushed washer that was reused, or a filter with the old rubber gasket still stuck to the housing under the new one. If your leak began within a week of a service, say so, because it changes where we look first.

Front and rear main seals are the more serious ones. The rear main sits between the engine and the transmission and leaking one is a labor-heavy job. The front, behind the crankshaft pulley, is more accessible.

Then there are the leaks that are not gaskets at all: an oil cooler line, an oil pressure sending unit, or a filter housing gasket that has hardened.

Why finding the source is harder than it sounds

Oil does not drip where it leaks. It leaks, then travels, carried along the engine block and across the underside by airflow at speed and gravity at rest, and it can land a foot or more from where it came out.

That is why a visual glance underneath frequently gets it wrong, and why people replace a gasket only to find the leak still there a week later.

The reliable method is to clean the area thoroughly first, using a degreaser to remove the accumulated film that makes everything look wet, then run the engine and look for fresh oil against clean metal. With the surface clean, the highest wet point is the source.

Where that is not conclusive, a fluorescent dye added to the oil and a UV light traces it exactly. The dye circulates with the oil, glows under the lamp, and shows the path from the actual source rather than the point where it drips off. On a car with several old leaks overlapping, that is often the only honest way to tell which one is doing the damage.

Being straightforward about this: on an older engine with oil over everything underneath, there is frequently more than one leak, and part of the job is telling you which one is worth fixing and which one you can live with.

How much oil loss is too much

Some consumption is normal, and manufacturers publish figures that surprise people. Many engines are considered acceptable losing up to a quart every 1,000 to 2,000 miles, and some performance engines are specified looser than that.

What matters more than the absolute number is the change. An engine that used no oil for five years and now needs a quart a month has developed something, and that is worth investigating regardless of whether the figure sits inside a specification.

The practical habit is to check the dipstick every couple of fill-ups, cold, on level ground. It takes a minute and it turns a vague worry into a number you can act on. Knowing you lose half a quart in 1,000 miles is useful. Knowing the level is somewhere below full is not.

The other question worth asking is whether it is leaking or burning. A leak leaves evidence on the ground and on the engine. Burning oil leaves none, and shows instead as blue-grey smoke from the exhaust, usually on startup or on hard acceleration. An engine that loses oil with no drip anywhere is burning it, and that is a different investigation involving valve seals or piston rings.

What we do, and what it costs

We come to the car, confirm which fluid it is, check the level and condition, and then find the source properly rather than guessing from the puddle. That means cleaning the suspect area, running the engine, and where necessary using dye and a UV lamp to trace it back.

You get a written finding that names the source, says how serious it is, and gives you a price for the repair. Where there is more than one leak, we tell you which one to deal with and which one can wait, because on a high-mileage engine that distinction is usually where the money is.

Diagnosis starts at $95. Oil change labor is separate and starts at $70, with the correct grade of oil and a quality filter quoted for your specific car, and it is worth pairing the two if the car is due anyway, since fresh oil makes a subsequent leak much easier to see.

Some leaks are straightforward driveway repairs and we do them on the spot. Some, a rear main seal being the obvious example, need the transmission out and are not honest driveway work. We say which is which rather than starting something we cannot finish well.

We cover Flushing and the rest of Queens, Brooklyn, Manhattan, the Bronx, Staten Island and Long Island. If the red oil pressure light is on, leave the engine off and tell us where the car is.

Common questions