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5 Reasons Your Car Might Be Losing or Leaking Oil

Wrench Wench has been in love with automotive mechanics for decades. She loves sharing advice with fellow DIY mechs and curious cats.

Dear Wrenchy, why is my engine leaking oil?

Dear Wrenchy, why is my engine leaking oil?

Why Is My Car Losing Oil?

Oil leaks and losses are one of the most common reasons that drivers bring their cars in for inspection.

It could be a tiny pinhole leak in a gasket, an obvious gusher from a bad seal, or a leak from a myriad of origins. In any case, it's vital to find the source of your car's oil leak and diagnose which repairs need to be made in order to resolve the leak and prevent your oil from leaving the place where it's needed most—inside your engine.

1. Burning Oil

Inside the heart of your engine is the combustion chamber, where all the magic happens. Normally, oil is kept out of this chamber by your piston rings and valve seals. If something happens to either your rings or valve seals, your oil will begin seeping into your combustion chamber where it will get partially digested and come out as a foul blue-gray smoke.

If your rings or valve seals are leaking, you may notice your oil is disappearing, but unless there are bad gaskets or other holes leading to the outside of the engine, then you likely won't see any oil on the ground or the engine. This is because oil from a small leak of this type, for example from just one partially warped piston ring or just one bad valve, will likely get burned up in the combustion process. If the problem becomes chronic and multiple rings or valve seals go bad, then the car will likely stop running as oil floods the combustion chambers and removes your car's ability to process fuel.

Sadly, if this happens, you're looking at some hefty expenses for repairs, especially if you need to go to a shop, which is highly recommended for any vehicle you can't risk losing.

Thankfully, while it is definitely an upper-level DIY project, if you do decide to save some labor costs by doing it yourself, it's not as scary to change valve seals or piston rings as it might seem at first thought. The only thing to really keep in mind is that you'll want to replace any seals, gaskets, or heat-sensitive bolts along the way, and throughout the process of dissection and re-installing everything you took out, you are going to want to decide on a plan of organization BEFORE you get started. You'll also want to check ahead of time to see if you might need any obscure specialty tools.

2. Improper Installations

While it's a much more common occurrence after a DIY or shade-tree gasket change, even professional mechanics make the mistake of improperly installing one of the many gaskets that keep oil IN your car where it's supposed to stay. The most common reason this happens and gets missed, is that someone over-tightened an oil pan gasket or valve cover gasket or didn't distribute the tightness evenly across the whole gasket. When this happens, it can cause the gasket to get "squished," which creates a place for oil to escape. And depending on how improperly tightened the gasket is, this simple error could result in only a "pinhole" leak, or it could become a pretty sizable gush. Virtually the same thing can happen when replacing an oil filter, which is much easier to over-tighten or even install crooked than you might think.

It's also not uncommon to have a new gasket installed before all surfaces have been properly scraped clean of all the old gasket leftovers, which can result in uneven gaskets and cause leaks in just the same way as if you'd over-tightened it in one corner.

Fortunately in most cases it's not difficult to fix a leak caused by an improperly installed gasket, though that doesn't mean it won't be without any challenges, especially in terms of keeping yourself from getting too frustrated with a gasket mulligan—the biggest source of doing it wrong TWICE (been there!)

So as long as you keep a level head and remember that it happens to everyone more often than you can imagine, you or your mechanic can dive back in and get that gasket issue corrected.

Wrenchy says most oil leaks are easy to fix yourself!

Wrenchy says most oil leaks are easy to fix yourself!

3. Holes! Holes! Holes!

Ohmergosh! Holes are another common source of oil leaks, and they can often occur on brand new gaskets for no apparent reason, which I can tell you from personal experience can be ESPECIALLY frustrating.

What is much more common, though, is to find holes in older gaskets or seals in higher heat and stress areas, such as your head gasket, or the rear main seal, which is supposed to keep oil from leaking into your transmission and tranny fluid from mixing into your engine.

Sadly gaskets aren't the only part of your engine that can develop holes. It's fairly common to accidentally puncture your oil pan lid, as is accidentally poking a hole in that brand new oil filter you just struggled to install.

If you're really unlucky, you might get to see a valve rod shoot through the top of your valve cover, the bottom of your oil pan, or even out through the side of your engine block. Such disasters are never cheap to repair, yet are almost always fascinating to examine and are almost always accompanied by a wild story.

Thankfully, most holes in gaskets just develop because the gasket is old. They can often be temporarily sealed with liquid gasket sealer until you can get in and replace it or get your car into the shop.

4. Cylinder Head Trauma

A much less frequent source of leaking oil is a cracked cylinder head or engine block. Sometimes you won't even see any oil on the engine or ground when this happens. This is usually because the oil is leaking INTO your coolant system, rather than out onto the ground where you would expect to see it. Regardless, in either situation, you can often confirm this diagnosis by checking your oil cap and coolant cap. One or both will be muddy brown and will likely smell like syrup and oil.

5. Broken Dipstick Tube

Yes, this can happen, and it is one of the most irritating repairs to have to perform on some vehicles. On my '93 Jeep Wrangler, the dipstick tube was super easy to replace. On the other hand, on a customer's '82 Chevy Caprice, it took me three days to find the leak, five days to wait for the dealership to order the part (that strangely no one else carried), and another two days to get it installed, followed by one extra day just to get the exhaust back on without breaking the new dipstick tube. Not cool!

Inspecting for Oil Leaks

Inspecting for Oil Leaks

More Possible Causes for Oil Leaks

In addition to checking out the above possibilities, you could keep in mind these common sources of oil worries:

  • Your oil level. If you're seeing oil on the ground but your dipstick reads more than full, you've overfilled the engine.
  • Spills. If you're seeing oil on the ground but aren't seeing any lost oil from the dipstick, it could be that some oil got spilled and you're just seeing the remaining oil that's still dripping down off the engine.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: What parts of the engine of a car can oil leak from?

Answer: Valve Cover Gaskets, Head Gasket, Rear Main Seal, Front Main Seal, Timing Cover, Oil Pan Gasket, Oil Drain Plug, Oil Filter, Dip Stick Inlet, Crack in the Block, Oil Cap, and anywhere that water can leak from if the block or head gasket has ruptured and allowed oil and water to mix.

Question: I have replaced the crank and timing belt seals. The oil pump area, valve covers, sump seal and right side of the engine are all free of oil leaks. Yet when I finished these repairs and drove home (about 35km) to inspect everything, I noticed I'd lost 2 liters of oil and the leak had become worse. What should I do?

Answer: With this limited information; especially not knowing what year or make of vehicle you're working on, the best I can offer is that it sounds like the seal around your crack shaft and/or timing case are not seated properly or possibly broke when you were buttoning up your repairs. This isn't entirely uncommon, especially if the oil seal was reused, if the new seal wasn't properly lubricated, or if the outer casing bolts were over-tightened. I would recommend pulling everything back apart and inspecting it all. Even if you're not able to see exactly what went awry, using great caution when you put everything back together, will likely resolve your leak.