Other than PCV valve, what causes engine oil to go bad quickly?

It was a surprise that the car engine oil was pitch black - I use Mobil 1 and m/c said every 6k - I do every 5k. 1999 Acura Integra with 95k

The PCV valve was found to be bad and replaced. At 80k I did the complete timing belt. New spark.

Curious anything else could be wrong?

How many months does it take you to rack up 5k miles? What type of driving do you do (mostly hwy, mostly city). What is your average trip length?


What kind of driving do you do?

Granny style?

young punk?

The vent from the valve cover to the air filter housing needs checking.

Are you SURE it only has 95K miles on it? How long have YOU owned it?

Sure 95k; Owned it since 04 from 38k miles. No commute on this car.
Both city and Hwy driving - drop kids at school. The driving hasn’t changed but this time, at 5k, the oil was black. Been using Full synthetic for a while now and changed every 5k. At last change, the m/c told me that he could see through the oil when draining it.

Could you elaborate on “vent from the valve cover to the air filter housing needs checking”?

Has it started to burn oil?

Crankcase vent…Be sure the crankcase is getting filtered air…If the tube is damaged, unfiltered air can be drawn into the crankcase, contaminating the oil prematurely…

The crankcase vent is a rubber hose the diameter of your thumb +/- that connects to the air filter housing at one end and the top of the engine at the other.

The idea of unfiltered air gtting drawn into the engine could be further investigated: inspect the air filter, its housing, the gaskets that should completely seal the gap between the filter and housing, and the “plumbing” (including hose clamps) and gaskets) between the filter and the throttle body. Any leaks will probably leave a smudge on the inner surface of the air filter system at the site of the leak.

The color of the oil is not really much of an indication of its condition. If you want to know if your oil is capable of doing its job lubricating your engine, you really should get a used oil analysis.

Having said that, I recently got some oil leaks fixed on my high mileage car, and I noticed a difference in how the oil looks on the dip stick. It appears cleaner than it did before the repairs.

Running rich, aging rings, or aging valve seals will make the oil get dark more quickly, it adds more carbon.

Color is not a good indicator. Try putting fresh oil in a Diesel and idle for a minute. It’ll be black as coal. That oil is still perfectly good.

One thing that will contaminate your oil quickly, a bad thermostat. Your car needs to heat up fully to drive off water and byproducts from cold starting. If your car never heats up fully it will also run rich, adding carbon and washing oil from the rings.

Old rings or valve seals are not worth the trouble until oil consumption is high or compression is low.

Thanks @Benjamin Madore & others.
There seems a lot in it - I will observe the car or show it to some experts.

There are a lot of things that can cause oil to become discolored/darkened quickly. Please note that the oil color doesn’t necessarily mean it isn’t lubricating properly, though I would change it too if it was pitch black. You also might consider having an oil analysis done–it will tell you if there are any contaminants worth worrying about, how much life was actually left, and if you can expect engine problems.

Things that can make oil go dark quickly:

-contamination from old oil left in the engine, a filter that wasn’t changed, or existing sludge in the engine.
-a malfunctioning PCV system
-excessive blowby from bad rings or contamination from a bad head gasket or intake gasket on some engines. (or soot from diesel engines)
-an engine that’s near the end of its life, with worn bearings, excessive clearances, etc. will “beat up” oil fairly quickly, resulting in the oil darkening.
-running an engine low on oil, which will beat up the remaining oil
-an engine that never gets hot enough to cook off water and other volatiles, possibly due to a malfunctioning thermostat or in a car that’s driven on only short trips, especially in cold climates.

I’m curious as to what your oil consumption is. You say you change it every 5K, but do you ever check it between changes?

If you don’t, that could be the root cause of your problem. Allowing the engine to run with lower than recommended levels of oil creates a lubricant that contains more dilutants, more crud, and less capacity to absorb and dissipate heat than running the proper levels. Just as a tablespoon of Nestle Quick makes a 10oz glass of milk much darker than it makes a 16oz glass of milk. Repeatedly running low on oil promotes premature cylinder wear, and that can manifest itself as oil becoming prematurely diluted and contaminated.

Understand that just because the oil light doesn’t come on does NOT mean the oil isn’t low. In your car the light only illuminates when the level gets so low that it drops below the pump’s pickup tube, the pump’s supply goes away, and the system loses pressure.

Understand also that the discoloration is not the oil going bad, it is that those thing sin the engine that produce contamination of the oil are producing more of it. The oil is doing its job by suspending and retaining those baddies. To solve the problem, you need to figure out where the baddies are originating from.

So, do you check you oil routinely and how much is your engine using?