Why You Shouldn’t Overfill Your Engine Oil

Unlike other vehicle problems, overfilling the engine oil is typically caused by simple human error. This can occur when topping off the oil or after an oil change. And while removing excess oil is easy, there can be consequences if you fail to notice it as soon as possible.

That being said, the risks and consequences vary with the engine platform as well as how overfilled the crankcase happens to be after oil is added.

What Happens When You Overfill Engine Oil?

Excessively overfilling with engine oil may cause the engine oil to foam in the crankcase. It may also cause oil pressure issues/leaks, etc.

While it’s never a good idea to overfill the crankcase, the issues that result from overfilling vary from engine to engine.

Some engines may exhibit intermittent labor knock accompanied by white smoke. Others may vibrate like something is out of balance. The symptoms vary, but the engine isn’t always damaged, although it can be if the oil is much over full.

Some engines when overfilled with engine oil may exhibit intermittent labor knock accompanied by white smoke. Others may vibrate like something is out of balance. The symptoms vary, but the engine isn’t always damaged, although it can be if the oil is much over full.

– Richard McCuistian, ASE Certified Master Automobile Technician

Foaming and Potential Engine Damage

Overfilling raises the level in the oil pan too high, causing the crankshaft to whip the oil into a foam, which doesn’t lubricate as well. If the vehicle is driven enough with foamy engine oil, it can wear out the bearings.

Increased Oil Pressure

Overfilling may also raise the crankcase pressure as the crankshaft rotates and splashes through the excess oil to the point of overwhelming the PCV system. The increased crankcase pressure may strain seals and gaskets to the point that they begin to leak excessively.

Oil Leaks

Overfilling engine oil may cause leaks that may result in the following:

• Increased metal-to-metal contact between engine components due to engine oil foaming, resulting in accelerated wear.
• Radiator damage due to engine oil leaking into the coolant system and creating engine sludge. (not likely, but possible).
• Smoke due to oil dripping onto the exhaust manifold.

Reduced Performance

The high oil pressure level and foaming may reduce engine power and performance due to the high oil level affecting free crankshaft rotation.

How to Determine If Engine Oil Is Overfilled

One symptom of an overfilled engine oil is a thick white smoke emanating from the exhaust pipe while driving (this may be intermittent and accompanied by a pinging or spark knock). You can confirm it’s due to overfilling by allowing the engine to sit for at least an hour to get a more accurate reading on the dipstick. Afterward, follow the steps below:

• Step 1: Ensure your vehicle is parked on even ground for a more accurate reading. Turn off the engine and open the hood.
• Step 2: Look for the dipstick housing, usually in a small tube that connects to the crankcase.
• Step 3: Pull out and clean the dipstick, and use a rag or paper towel to wipe the oil off. Check the tip and look for the two lines.
• Step 4: The lower line indicates the engine level is one quart low, while the upper line shows if it’s full. Some dipsticks mark these as safe (upper) or add (lower).
• Step 5: Insert the dipstick slowly into the tube to avoid splashing the oil and messing with the reading. Push it down and withdraw the stick to check the tip.
• Step 6: If the oil level is above the add/upper line, you have overfilled the engine oil.

How to Remove Excess Engine Oil

There are a handful of ways to remove excess engine oil, including draining, using a vacuum extractor pump, and seeking professional help.

Draining

To drain excess oil, you’ll need the following:

• Fresh oil
• Oil drain pan
• Wrench
• Rag
• Jack and jack stands

Afterward, follow the steps below:

• Step 1: Start the engine, let it idle for 10 minutes, and drive around for an additional 15. Warm oil is easier to drain and suspended contaminants will drain out with the oil rather than settling in the bottom of the oil pan.
• Step 2: Park the vehicle and use a jack and jack stand to elevate the car off the ground or drive it up on ramps designed for the purpose or park it over a ditch so you can get under it (believe it or not this is a good method if you have an available low spot).
• Step 3: Place the drain pan beneath the drain plug to catch the oil. Use the wrench to loosen the drain plug.
• Step 4: Let the oil drain for at least 10 minutes. Pull out the dipstick and clean it with a rag.
• Step 5: Remove the old oil filter while setting the drain pan underneath to catch more oil. Make sure you find the gasket to be sure it isn’t stuck to the filter head on the engine.
• Step 6: Replace the oil drain plug before adding new oil. Insert the plug in the hole and tighten it by hand. Install a new oil filter, first lubricating the oil filter’s rubber seal with a bit of clean engine oil.

Once the oil level is normal, start the vehicle, watch the oil light go out, and the kill the engine and check for leaks, particularly around the oil filter. Check for unusual noises. If you hear some, it’s best to take your car to a mechanic to have it inspected.

Using a Vacuum Extractor Pump

You can buy vacuum oil extractor pumps for under $100. These allow you to manually suck the oil out of your car using a straw inserted into the dipstick tube. These pumps could save you money since you won’t need to remove and change all the oil, unlike draining.

Seeking Professional Help

If your vehicle still exhibits the symptoms listed above after draining the excess oil, it may be best to seek the help of a certified mechanic. They should be able to thoroughly inspect your engine, identify any issues, and conduct the appropriate repairs.

How Much Engine Oil Does a Vehicle Need?

Engines typically need five to ten quarts of oil, but look it up in the owner’s manual to be sure.