How many miles for black oil?

[camrydriver111]

When I was looking at used cars at the lemon lot a lot of them had pitch black oil on the dipstick. The salesman wasn't too concerned and it seemed like it was normal to him.

How many miles does it take for the oil on your dipstick to turn black? Provided the engine does not have major mechanical issues. How long did those lemon lot cars go without an oil change?

I am also curious about what causes the color change in oil. People say it's suspension of combustion byproducts, and "cleaning". Can it also be the physical breakdown of oil? I would think that the breakdown of VI during an OCI would result in a bigger viscosity change than suspension of byproducts unless the concentration of those byproducts is really high. Would the breakdown of VI and base oil also be accompanied with a color change?

 

[Nick1994]

I would never buy a car that had pitch black oil on the dipstick unless it was a diesel.

I went and looked at a Camry once and pulled the dipstick and there was nothing on it. The salesman said it was no big deal and started the car anyways, it ran terrible. Also had nothing in the radiator.

I also went and looked at a Civic once and the guy selling it said he just had the oil changed at a quick lube place 30 minutes before I showed up. I pulled the dipstick to see black oil and told him he was a liar.

 

[donnyj08]

run away. If they couldn't spare $15 for some supertech and a jobber filter for their cars then id be Leary of anything they sell.

My silverado can be at 0% on the OLM and have 9k miles on the oil and the oil will only be a medium brown.

I flip several cars a year and i always change the oil in them unless it is obviously clean. Conventional oil is cheap as are Jobber filters.

 

[buck91]

My f150 still has brown oil with a hint of transparency on the dipstick when it gets changed around 8500 miles. Agree with above post unless it's diesel then I'd be questioning why it's.black.

 

[zorobabel]

On cars I've had, 10k on syn or dino oil and the oil still drained dark brown, while it looked ok on the dipstick.
I would say at least 15k to 20k on the oil in those cars if the engines are in decent shape.

 

[MinamiKotaro]

The Bug turns oil black pretty fast. The Saturn will have turned most oil pretty dark by the time the CHG OIL light goes off (usually about 7500 miles).

Worst used car fail I've seen was one I test drove that had a cracked fuel rail. Fuel vapor was spraying into the engine compartment and the car went from full to 3/4 of a tank in about a mile. The salesman treated me like I was an idiot for thinking it was a problem.

 

[Wolf359]

You're not supposed to go by the color of the oil, just how long it's been in there. In theory if it looks too clean, how good of a cleaning job do you think the oil is doing? Only way to really tell is by a used oil analysis. Otherwise people would just pull out dipsticks and be able to tell just by looking. You can't.

 

[MinamiKotaro]

Originally Posted By: Wolf359
You're not supposed to go by the color of the oil, just how long it's been in there. In theory if it looks too clean, how good of a cleaning job do you think the oil is doing? Only way to really tell is by a used oil analysis. Otherwise people would just pull out dipsticks and be able to tell just by looking. You can't.


True, that. I always figured that turning black meant it was doing what it's supposed to.

 

[Merkava_4]

Originally Posted By: camrydriver111
I am also curious about what causes the color change in oil.


Black is the accumulation of lots of dirt; plain and simple.

 

[ExMachina]

Originally Posted By: Merkava_4
Originally Posted By: camrydriver111
I am also curious about what causes the color change in oil.


Black is the accumulation of lots of dirt; plain and simple.


Dirt, and oxidation (burnt oil) from not changing it in a long time.

 

[OneEyeJack]

With used cars on a lot you should know that sometimes they change the oil but use non-detergent 30W oil. I will appear clear and bright even if the car does not sell for a few months.

You'll see nice clean oil but it many not indicate a nice clean engine.

 

[mongo161]

FWIK....cars on a used car lot have their oil changed to Bulk HD Diesel 15w40 oil in most cases.

The Bulk HD oil will quietly perform a few necessary tasks....tone done a noisy engine, leaky gaskets and seals will not drip oil quickly, the HD 15w40 oil will turn black fast, especially if the engine is dirty and the oil is doing its job by cleaning up any dirt or sludge.

Don't forget.....these vehicles are periodically taken out for a....."fast spin around the block" to keep the battery charged and have the tires filled with air.

 

[WiskyBadger]

I change the oil in any vehicle I buy as soon as I get home with it to assure new fresh oil and right grade. Also to make sure there is a new filter in it.