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Why Is My Car's Engine Using Too Much Oil?

Updated on July 26, 2017
Dan Ferrell profile image

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

High engine oil consumption doesn't happen only to high-mileage engines.
High engine oil consumption doesn't happen only to high-mileage engines. | Source

All cars consume oil, at different rates depending on the engine model, driving patterns, engine load, and maintenance history.

But excessive engine oil consumption should be taken seriously. If you know your engine is consuming too much oil, diagnose the problem, the sooner the better.

Sometimes the source of the problem is evident, like a damaged gasket. When the source isn't that obvious, this guide will help you make the diagnosis by directing you to common sources of oil consumption, internal and external.

Before you start your diagnostic, gather as much information about the issue. These clues will help you narrow down your troubleshooting procedure to a few components or system. For example:

  • Does the oil warning light on the dashboard illuminate?
  • Have you found oil stains on the floor?
  • Do you see blue-gray smoke coming out of the tailpipe?
  • Can you hear odd noises coming from the engine?

The sections that follow will help you determine:

  • whether your engine is indeed consuming too much oil,
  • how to measure your engine oil consumption,
  • which external issues might cause the problem,
  • and which internal sources might cause the problem.

An oily tailpipe may indicate an internal oil leak.
An oily tailpipe may indicate an internal oil leak. | Source

I. Is My Engine Consuming Too Much Oil?

Vehicle engines consume a small amount of oil as part of their normal operation. But how much is too much? At what point should you be concerned?

Normal oil consumption rate varies with engine size, make and model. If you want to know if you should worry, look for these additional signs. If you:

  • see a spot or puddle of fresh oil on the floor where you park,
  • add one quart or more of oil every 3000 miles,
  • see blue-gray smoke coming out the tailpipe, or
  • feel a greasy film inside the tailpipe,

it's time for a diagnostic. Your engine has either an external or internal oil leak.

2. How to Measure the Engine Oil Consumption Rate

Your engine may not show signs of blue-gray smoke. Still, you may suspect you're adding too much oil between oil changes.

To measure your engine oil consumption rate, do the following test:

  1. Park your car on a level surface and wait about 20 or 30 minutes to allow the oil in the engine to drain into the oil pan.
  2. Open the hood and pull out the oil dipstick. Wipe it clean using a shop rag.
  3. Reinsert the dipstick completely into its tube and pull it out again. Make sure the oil level marks full. Otherwise, add the correct type and amount of oil for your engine to make sure to bring up the level to the Full mark.
  4. Once the engine has the correct amount of oil, jot down the number of miles the odometer shows and save this number in a safe place.
  5. Drive your car as you normally do, check oil level at least once a week (or before, if you think it necessary). And keep an eye on the odometer. You want to know when you've driven 3000 miles.

Now, if you need to add a quart of oil at or before 3000 miles—because the oil level on the dipstick is at the Low mark—your engine is consuming too much oil. The engine may have an external or internal oil leak.

If the engine has used over half a quart but less than a quart, you may have a small leak.

If the engine used half a quart or less, you might be within a reasonable limit, but you still need to watch for oil consumption.

Why is My Brand-New Car Consuming Too Much Oil?

Owners of some new, or relatively new, car models complain that they have to add oil between oil changes. Although manufacturers of some of these vehicles say oil consumption between changes is normal, Consumer Reports says not everyone agrees.

Once you confirm that your engine has started to develop an oil leak, you need to find the source.

External oil leaks are sometimes easier to detect because they may leave behind an obvious trace of fresh oil somewhere around the engine or on the floor where you park. Internal oil leaks, though, are not that obvious, unless you can see a cloud of blue-gray smoke coming out the tailpipe.

If you suspect your engine has an oil leak but can't pinpoint the source, the next two sections will help you diagnose the problem.

Internal oil leaks are harder to diagnose.
Internal oil leaks are harder to diagnose. | Source

3. Sources of External Oil Leaks

External oil leaks are perhaps the most common sources of high oil consumption.

These type of leaks may come from worn out or crushed gaskets or seals, or a damaged part.

Depending on the severity and the source of the leak, you may see a small puddle of oil on the floor where you park.

Locating the Leak Source:

1. First, visually inspect the PCV valve and connecting hoses and grommets (here's more about checking the PCV system). If the valve is stuck open (possibly from sludge), or a grommet or hose in the system is leaking, it may allow a constant flow of air—and oil—out of the crankcase.

2. If oil is leaking onto the floor, visually inspect the area directly above the puddle of oil

3. If you don't see signs of leaks on the floor or ground anywhere around the engine, do the following to search for the leak.

  • You may need to lift the front of your car using a floor jack.
  • Secure the vehicle on jack stands, block the rear wheels and engage the parking brake.
  • Look for darkened, wet spots around the engine. Follow the wet area to the highest point in the engine.
  • Steam- or pressure-wash the engine if it is so covered with dirt or grease that you can't trace the leak to the source.
  • Then look over the engine to try to trace the oil leak back to its source. This could be a gasket (oil pan or valve cover), a seal (engine front or rear), or a damaged component (oil pan or drain plug).
  • If the leak source seems to come from high around the cylinder head, check the valve cover. Verify that the valve cover gasket or O-ring is still in good shape. Then make sure the bolts are tight (consult your vehicle repair manual for the correct torque for your car model).

4. Another common source of leaks is the oil pan underneath the engine. Inspect the condition of the oil pan gasket. Aso, make sure the bolts are tightened to the correct torque, and the drain plug and gasket are still good. Consult your vehicle repair manual.

5. If the leak seems to come from the engine oil filter area, check that the filter is tightened properly. If you just replaced the filter, verify that the old filter gasket was removed. Then, check that the oil pressure switch is not damaged or loose.

6. If the leak seems to come from the front of the engine, check the front seal for damage, or the gasket in the oil pump housing. You may need to remove the timing belt cover.

7. If the leak is in the rear of the engine, the rear seal may be leaking. To inspect the rear seal, though, you would need to separate the transmission from the engine.

8. Sometimes the leak is so small that you won't be able to find the source through a normal visual inspection. You may want to wait for the leak to become more noticeable, or you may want to use an oil leak detection kit.

Worn-out piston oil rings will cause oil leaks into the chamber.
Worn-out piston oil rings will cause oil leaks into the chamber. | Source

IV. Sources of Internal Oil Leaks

Just like external oil leaks, an internal oil leak in your engine may show a telltale sign. You may detect a greasy film (or residue) inside the tailpipe of your car. That's oil coming through the exhaust system from the combustion chambers.

If the problem is severe enough, you may see blue-gray smoke coming out the tailpipe. Don't confuse this with white or black smoke. You'll also notice a gradual drop in engine oil level.

The blue smoke comes from engine oil being burned inside the combustion chamber. Besides being a sign of the dangers associated with an oil-starved engine, oil going through the exhaust system will eventually destroy your catalytic converter because of the anti-wear additives in the oil.

How can engine oil find its way into the combustion chamber?
Abnormal oil leaks into the combustion chamber can come from any of these sources.

Piston rings or valves may allow a very thin film of oil to pass into the combustion chamber. But more can get through if you have any of these problems, either because of normal wear and tear or poor maintenance:

  • worn out or broken valve seals
  • worn valve stems or guides
  • worn out, stuck or damaged piston rings
  • worn out cylinders

A clogged crankcase ventilation system or valve. Sludge and varnish can build up and prevent blowby gasses from recirculating. The restriction will increase crankcase internal pressure, which in turn will accelerate the wear of piston rings, gaskets, and seals, allowing oil to escape into the exhaust system or leak through.

Bearings. High mileage or poor maintenance will wear down bearings and can damage them. Worn-out bearings will flood the cylinders (from below the pistons) because of the excess oil the bearings are circulating. The pistons and piston oil-control rings might not be able to handle the increase in oil throw. Rings may stick, allowing oil to filter into the combustion chamber. Similarly, connecting rod and camshaft bearings can flood pistons and valve stems and guides. The vacuum will pull the extra engine oil collected alongside the valves into the combustion chamber.

A vacuum or compression engine test will help you check for worn piston rings, cylinders and valves. Consult the vehicle repair manual for your model (Haynes is a good cheap aftermarket manual).

Ignition timing problems may cause internal leaks as well.
Ignition timing problems may cause internal leaks as well. | Source

Unsuspected Ways You Are Increasing Engine Oil Consumption

Your vehicle engine doesn't have to accumulate too many miles or have a worn-out gasket or seal or a damaged part to start leaking oil. There are some unexpected ways you can encourage oil consumption or leaks:

  • Pulling heavy loads, especially in mountainous terrain.
  • Switching to a lighter weight oil than the one recommended by your car manufacturer: for example, switching from 15W-40 to 5W-30 or 10W-30.
  • Switching to a low-quality oil can promote carbon buildup around piston rings, leading to ring malfunction and oil leaks.
  • Operating your vehicle with an overheating engine (bad cooling system, bad cooling fan or thermostat) can create hot spots around one or more cylinders. Hot spots will distort the cylinder and allow oil to leak into the combustion chamber, leading to high oil consumption.
  • Failing to change dirty engine oil will accelerate the deterioration of gaskets and seals and the wearing of pistons, piston rings, cylinders, and bearings. This results in higher oil consumption.
  • Operating the engine with ignition timing problems may lead to excessive oil consumption as well. If the cylinders and valves are not synchronized, vacuum may pull engine oil through the valve stems and guides into the combustion chamber.

Preventing these problems from occurring or fixing them when they appear helps you control engine oil consumption and more serious problems in the future.

Preventing excessive oil consumption is even more important now that many modern vehicle models come with extended oil change intervals. So monitor your engine oil level and condition more frequently, at least once or twice a month. And change the oil as necessary; don't wait for the manufacturer's suggested interval.

When your engine leaks oil, remember that the damage is not confined to your engine. Leaking oil contaminates the soil, and burning oil scatters hazardous particulates into the atmosphere. So repair the oil leak as soon as possible.

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