What Happens When You Overfill Your Car With Oil?

When an engine has too little oil, bad things can happen: Friction between moving parts increases, the engine may run hotter and, worst case, moving parts seize when they become starved for lubrication.

Bad things also can happen when there’s too much oil. Overfilling with oil can cause foaming, which turns a slippery lubricant into a sudsy fluid with air bubbles that diminish the lubricating and cooling properties. Frothy oil also is harder for the oil pump to distribute around the engine, so some moving parts might not receive as much oil as they need, increasing wear and raising the risks of engine damage. 

Can You Drive a Car With Too Much Oil?

No, you shouldn’t drive a car with too much oil. Too much oil can cause it to foam which causes air bubbles to enter the oil pressure channels inside the engine; this is bad for the engine and can cause it to seize if you are unlucky. But if you only overfilled it slightly 0.2″ or less below the max mark, you don’t need to worry too much in most cases.

How much oil does a car need?

That depends. Look for specifics in your vehicle owner’s manual, but many engines require between 4 and 6 quarts. Typically, the oil drains into a pan at the bottom of the engine, below the crankshaft. If the pan is overfilled, the crankshaft can act like a high-speed blender that churns the oil and creates foam.

The crankshaft is where engine speed is measured, and it spins rapidly whenever the engine is running. For example, if the tachometer reads 2,500 rpm at 75 mph, that means the crankshaft does a complete revolution 2,500 times each minute; floor the throttle and it can reach 5,000 rpm or higher.

Overfilling also increases oil pressure, putting more stress on seals and gaskets that keep oil from leaking out of the engine or going places it shouldn’t on the inside. Over time, the added stress accelerates wear on those seals and gaskets. Overfilling often occurs because repair shops pump fresh oil from bulk containers instead of pouring it from quart- or gallon-size containers. Holding the pump trigger too long can easily add extra oil, and the technician might not check the dipstick — and even if they do check it, oil takes time to drain into the pan, so they might get a false reading of the oil level right after pumping in fresh oil.

Checking the oil dipstick when a vehicle is on flat ground and the engine is cold will give an accurate reading of the level. If the oil level is a little above the full mark, that shouldn’t cause problems. If it’s overfilled by half a quart or more, or foam shows on the dipstick, the best fix is to have the oil drained and refilled to the proper level.

How To Fix Overfilled Oil?

To fix overfilled oil, you need to drain the engine oil. There are two main methods of getting oil out of the engine and these are to either use a suction pump or drain it through the oil plug. Draining it through the oil plug is the easiest way, as it usually doesn’t requires any special tools.

The advantage of using a suction pump to get the oil out is that you don’t have to raise the car and crawl under it. But you need a special pump and an air supply for it, and most people don’t want to spend money on a tool they will only use once or twice.

The most common method is to drain it the traditional way through the oil plug. If you are not used to cars this can be a bit messy and sometimes difficult so you may want to have a mechanic do it if you are unsure. Here is how you can drain the oil through the oil plug:

• Raise the car and place jacks under it for safety
• Remove the cover under the engineif present.
• Locate the oil plug (Use a repair manualto locate it if unsure)
• Remove the drain plug and drain it into a bucket with the amount you think you overfilled it with (usually 1 quart).
• Replace the oil plug and tighten it to specification.
• Refit the cover, and lower the vehicle to the ground.
• Start the engine for 3 minutes and turn it off.
• Wait 5 minutes and check the oil level again.