Where Is That Oil Leak Coming From?

A spot on the driveway tells you the car is leaking. It does not tell you from where. Oil runs down the engine, gets blown backward by airflow at speed, and drips off the lowest point it reaches — which is often a foot or more from the leak. Guessing from the puddle is how people end up paying for an oil pan gasket when the valve cover was the problem.

First, is it oil?

Put a piece of cardboard under the car overnight. Engine oil is brown to black and feels slick. Transmission fluid is usually red or brown and thinner. Coolant is green, orange or pink and slightly sticky. Power steering fluid is thin and reddish or clear. Brake fluid is clear to amber and feels almost like light oil — and a brake fluid leak is the one that needs attention today.

The usual suspects, top to bottom

Valve cover gasket

The most common oil leak on engines with some age on them. The gasket hardens, shrinks and lets oil seep out the top of the engine. It runs down the sides of the block, drips onto the exhaust manifold — which is where the burning-oil smell after a drive comes from — and ends up on the ground below the front or middle of the engine. Usually a straightforward driveway repair.

Oil filter and drain plug

Worth checking before anything else, especially after a recent oil change. A double-stacked filter gasket, a loose plug, or a crushed drain plug washer causes a leak that looks alarming and costs almost nothing to fix.

Timing cover and front crank seal

Oil at the front of the engine, often thrown onto the belt and pulleys. A wet belt slips and squeals, which is sometimes the first symptom noticed.

Oil pan gasket

Oil along the seam of the pan itself, with a wet pan bottom. Often diagnosed incorrectly because oil from above ends up here anyway.

Rear main seal

Oil between the engine and transmission, dripping from the bell housing. Cheap part, expensive labor, since the transmission has to come out. This is one we confirm carefully before recommending, because a leaking valve cover or a cam plug at the back of the head produces a drip in exactly the same place.

Oil cooler and oil filter housing

Increasingly common on modern engines with plastic filter housings and oil-to-coolant coolers. Leaks here can also mix oil into the coolant, which is a separate problem covered in our post on head gasket symptoms.

Which leaks can wait

A slow seep that needs a top-up every couple of thousand miles is not an emergency. Watch the level, keep it full and schedule the repair. A leak onto a hot exhaust is a fire risk and a smell you will not enjoy, and gets moved up the list. A leak that is dropping the level between fills, or any leak on a car that is also losing coolant, gets looked at now.

The one that people wait on and should not is a leak they never see because it never reaches the ground: oil burning off on the manifold or being pulled into the intake. The dipstick is the only warning. Check it monthly. Our post on oil consumption covers that case.

Frequently asked questions

Will a stop-leak additive fix it?

Additives that swell seals can slow a minor seep, sometimes for a while. They do not fix a hardened gasket, and some cause other problems. We do not use them as a repair.

Can a mobile mechanic replace a valve cover gasket?

Yes. Along with oil pan gaskets on most vehicles, front seals, and filter housing seals. A rear main seal is a shop job on nearly everything. See what we do on site.

How much oil loss is normal?

A healthy engine loses very little between changes. If you are adding oil regularly, something is leaking or burning it, and it is worth finding out which.

Serving Charlotte and Mecklenburg County, including Matthews and Indian Trail. Call (754) 236-1714.