Car Leaking Oil After Oil Change – this is why


Changing the oil and filter is one of the simpler car maintenance chores, but sometimes even the simplest jobs can go wrong. Leaking oil is a cause for investigation, but don’t panic, in this post, we’ll get it figured out.

The top 4 causes of a car leaking oil after an oil change, includes: 

  1. Oil spill
  2. Drain plug leak
  3. Oil filter leak
  4. Oil filler cap leak

In this post, I’ll show you what to look for when your car develops an irritating oil leak. As this problem has only developed after an oil change, the problem is likely to be a simple fix.

1 Oil Spill

Car oil filling

Many times the simple and obvious answer is the correct answer. Spilling engine oil when filling is so common. Oil containers are full and judging where to aim the oil flow before it starts flowing is a skill you learn, but only after you perform dozens of oil changes. When oil misses its target, it flows down the front of the engine.

Another likely opportunity for a spill is the removal of the oil filter. Many filters are now fitted on the top side of the engine, meaning any spill flows down the front of the motor. 

In addition, some filters are fitted in awkward places which guarantees a spill, cleanup is sometimes just part of the job. This happens to the professionals too, and when it does we use a cleaning product like brake cleaner, which you can check out here on the Mechanics consumables page.

Simply spray the cleaner down the front of the engine, it follows the path of the spilled oil cleaning as it goes. The mess eventually drains off on the shop floor and the technician cleans the oil pan with a shop rag, problem solved.

However, if the oil pan splash cover has already been refitted (most likely) the lazy technician may decide to skip the cleaning, this results in a messy oil pan that drips. This is the kind of oil leak that solves itself, and likely won’t drip from more than a few hours, just until the pooled oil drains off.

Using a funnel and a rag, draped around the oil filler neck helps prevent a spill.

2 Leaking Oil Drain Plug

To remove the engine oil, the drain plug needs to be removed. And the drain plug is at the lowest point in the oil pan, meaning it’s important it makes a perfect seal. A leaking oil drain plug is a very common issue after an oil change. 

The most common causes of an oil drain plug include:

  • Oil plug washer leaks
  • Oil plug too tight
  • Oil plug too loose
  • Oil plug threads stripped

Oil plug washer leaks – Most manufacturers recommend replacing the sealing oil drain washer. A copper washer or crush washer is common. The crush washer resembles a miniature ring doughnut, when the plug bolt tightens, it crushes the washer creating a perfect seal.

While it is possible to reuse the same washer, doing so very often results in an oil plug leak. Some manufacturers recommend replacing the complete oil plug.

Oil drain plug too tight – Over tightening the plug deforms the washer beyond a sealing. A torque wrench is a tool used to tighten fasteners to a specific torque. Torque is measured in ft. lbs. (Feet Pounds) or Nm (Newton Meters). A common torque spec for oil pan plugs is 15-18 ft. lbs.

Of course, it’s OK to tighten the plug without a torque wrench, but you do need to use caution. Oil pans are made from a soft metal, over-tightening may cause more serious issues, which I cover below. 

If you prefer to use a torque wrench great, you’ll find a link to the torque wrench I use on the Mechanics tools page.

As a rule of thumb, tighten the plug by hand until it seats, now goes ahead and tighten the plug a quarter to a half turn and stop.

Oil drain plug too loose – Forgetting to tighten the oil drain plug, or not tightening sufficiently to make a good seal.

Oil drain plug threads damaged – Over-tightening a drain plug may cause the threads to strip. Oil pans are made from soft alloy and don’t like rough play. Stripped threads are a pain in the jacksie and will require a tap and die set and an oversized drain bolt to fix. 

A dripping drain plug in itself isn’t a huge problem, but if the motor runs out of oil it could be a very big issue.

Most makers will recommend replacing either the drain plug or a sealing washer attached to the plug.

3 Oil Filter Leak

Oil filter

Oil filters come in two flavors, an older style metal screw-on type and a cartridge type. The metal screw-on type is the older style filter. Most modern cars are fitted with the cartridge type filter. To replace the cartridge style filter, a plastic cap must be removed. 

Common oil filter oil leaks include:

  • Filter loose
  • Filter too tight
  • Filter seal fault
  • Wrong filter
  • Cracked plastic filter cap

Filter loose – Metal filters screw-on type filters are tightened by hand. Not tightening enough causes the pressured oil to sneak past the filter seal.

Filter too tight – Over tightening oil filters risks deforming the oil seal causing a leak.

Filter seal fault – An oil filter seal needs to be lubricated with fresh engine oil before fitting. A dry seal risks pinching when tightening, especially the cartridge type. 

The wrong filter – Filters come in many different sizes, although the filter may fit, it may not fit correctly. Cracked plastic filter cap – The cartridge type filter has a plastic retaining cap, as these caps age they become brittle and may crack. With the engine running and the oil system pressurized, the cap leaks.

4 Oil Filler Cap Leak

Forgetting to refit the oil filler cap is a very common cause of oil leaks. But more common than that is a worn-out oil filler cap seal. When the engine is working hard at higher rpm, internal engine pressure may cause oil leaks from around the seal. 

The fix is simple, replace the seal or the filler cap completely.

Check out all my favorite tools on the Mechanics tool page.

John Cunningham

John Cunningham is an Automotive Technician and writer on Rustyautos.com. I've been a mechanic for over twenty-five years, and I've worked for GM, Volvo, Volkswagen, Landrover, and Jaguar dealerships. My passion is cars. I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of car ownership, including buying advice, maintenance, and troubleshooting.

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