Car Repair and Maintenance

Car Losing Oil but No Leak or Smoke [5 Reasons & Solution]

This maintenance publication explains the reasons for a car losing oil but no leak or smoke. Typically, your vehicle losing oil should be accompanied by leaks or smoke, but other factors come in in the absence of these factors.

You would get the oil light to come on but with no puddle underneath the vehicle. The first thing that comes to mind is replacing the oil, but you are certain that the oil change is too soon.

If you continue to replace or top the oil, you will be spending more money than necessary. This problem can escalate to a major breakdown, including overheating, if not fixed.

Reasons for Car losing oil but no leak or smoke

When your vehicle mysteriously loses oil, it is either burning the oil or there is an oil leak, similar to a gas leak.

Since you cannot find any visible signs of an oil leak, your car is burning the oil. Typically, you will not also get the notorious smoke that comes when there is a leak.

This, therefore, means that other components are responsible for the oil leak, including the failing rings and worn seal.

If you must replace the oil again, the mechanic should first inspect for internal or external leaks.

If no leaks are recorded, the chance is that your car is burning oil. This is a problem you need to fix to not only save cost but prevent major damages.

Worn components are typically responsible for engine oil seeping into the combustion chamber. Moreover, low-viscosity oil like 5W-20 will go to the chamber from the slightest wear.

If you do not see any leak or smoke, but your car is losing oil, below are the reasons and fixes:

  1. Worn PCV valve

PCV (positive crankcase ventilation) system is an important engine component responsible for eliminating any harmful gases the engine combustion process generates.

PCV works by routing excessive gases back into the combustion chamber to get burned again before going out through the exhaust.

A clogged PCV system will significantly increase the amount of oil blowback. As such, instead of removing combustion gases, the engine oil is sucked into the engine through the air intake.

How to fix Worn PCV valve 

If you find the PCV valve faulty, the solution is to get a replacement one.

Read also: DIY is possible for your clogged radiator

You can replace the PCV valve yourself. Do the following:

  • Find the PCV valve following your repair or owner’s manual. Normally, you should find it on or near the intake manifold. Some cars keep it on the valve cover.
  • Loosen the hose clamp where the PCV is connected and inspect the hose. You can replace any spongy, cracked, clogged, or pinched hose.
  • The next step is to remove the valve. The valve is held in place with a grommet in some cars to pull free. If the valve is screwed, get a wrench or unscrew it by hand.
  • Inspect the rubber grommet. If worn, consider replacing it.
  • Put the replacement valve into the rubber grommet or screw it in.
  • Finally, reattach the hose and firmly secure the clamp.

Drive the car for a while and monitor the oil level. If this fixes it, then you fixed the problem.

  1. Worn piston rings or cylinder walls

Piston rings create a seal against the cylinder walls to moderate engine compression, keeping combustion gases from escaping. Other functions of piston rings include the following:

  • Help the piston to travel smoothly up and down.
  • Move heat from the hot piston into the cooled engine cylinder wall/block.
  • Ensure that the combustion chamber is sealed.
  • Block pressurized combustion gases that may enter the oil sump.
  • Seal combustion pressure and control oil and blow-by.

Worn piston rings or failing cylinder walls stop the seal from functioning properly. Thus, a malfunctioning seal allows engine oil to enter the combustion chamber, which is the reason for the car losing oil but no leak or smoke.

How to fix Worn piston rings or cylinder walls

The solution is replacing the worn piston rings, which can be pricey.

Read also: if your car struggles to start but runs fine, here’s the fix

And unless you have the experience, a DIY is not advisable. Get an experienced mechanic to locate the position rings inside the engine.

Piston ring replacement involves disassembling the car and removing the engine to access worn rings.

  1. Worn valve seal

Valve seals are responsible for controlling the consumption of oil valve lubrication. Valves ensure system regulation and are designed for use in different engine types to control oil consumption and valve lubrication.

If the valve stem seals are worn, you will experience low oil levels. Remember that valve stem seals are designed to regulate oil consumption and lubricate the valve. However, failing valve seals do the complete opposite.

When the valve seal is worn, the oil may leak oil into the engine cylinders and then to the combustion chamber, which burns oil. Sometimes, you do not get a leak or smoke.

How to fix Worn Valve Seal

To replace worn valve seals, do the following:

  • Disassemble the engine down to the valve spring. This involves removing the cylinder head cover, push rods, rocker arms, and spark plugs.
  • Enable the air compressor and regulate the air to 60 to 90 psi.
  • Turn the crankshaft so the cylinder you replace and the valve seals sits on top center.
  • Use a screw to drive the compression gauge hose into the hole of the spark plug.
  • Connect the air compressor hose to pressurize the cylinder.
  • Use the valve spring tool to compress the valve spring and remove the valve keepers using a magnet. The spring retainer may get stuck. Use a small hammer to jar it loose.
  • Place towels around the area to hold the keepers into the engine.
  • Remove the spring.

After removing the old valve seal with pliers or screwdrivers, place the new one. Follow the reversed procedure to reassemble the engine.

  1. Failing head gasket

A blown head gasket can be the reason for the car losing oil but no leak or smoke. The head gasket stops liquids from entering the engine cylinders.

If the head gasket gets damaged is and broken, oil enters the combustion system, getting burnt. You may not also get smoke from the exhaust or a leak.

How to fix a Failing head gasket

The solution is to replace the blown head gasket. However, you need an experienced mechanic to do the job. Head gasket replacement takes time, so the replacement labor cost is high.

Read also: what makes your steering wheel too hard to turn?

5. Oil burning problem

As mentioned earlier, worn engine components allow oil to seep into the combustion chamber, which causes oil burning.

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Sometimes, you would get blue-tinted smoke from the exhaust, which indicates this issue.

It is also normal for some cars to take more oil than others but unusual oil consumption is not okay.

Losing oil can cause major damage to the car. You do not want to spend expensively, so you want the worn engine components fixed.

Final thoughts

Even though you cannot see oil leaks or smoke, an internal leak is possible in your car. It could even be too small for you to notice.

A vehicle can even leak oil through tiny cracks due to worn pipes, which do not leave a large oil puddle or cause smoke.

Your car will give a warning light about the oil even though you cannot find it. A mechanic may be able to check for hidden leaks.

Mechanics typically employ special tools during vehicle inspection to detect small cracks in the car system. Without these specialized tools, you may be unable to tell oil leaks independently.

Your car burning car oil will leave a hole in your pocket, resulting in significant component damages.

Contact a mechanic that will perform a thorough inspection and even an oil filter change to make up for a full-service oil change for your vehicle.



Latest posts by Bernard Juchli (see all)

Bernard Juchli

Bernard Juchli is an experienced racer, mechanic and team owner who trusts Avon Tyres.Bernard is the lead driver and force behind his Big Dog Garage Race Team. He is the General Manager and Chief Mechanic of Jay Leno’s Garage. Bernard and his crew of seven are responsible for all repairs, restoration and fabrication of Jay’s incredible automobile and motorcycle collection.

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