Sudden oil darkening. Why?

[aa1986]

I've read a few times that some people have oil that will turn from clean to dark at x,xxx miles every oci.

This has always intrigued me so thought I'd ask for theories on why this occurs.

I personally thought it could be due to the filter getting loaded enough that it begins to bypass at a particular mileage and that this is a repeatable occurrence. But I understand that such a reason doesn't stand up to the fact that some soot particles are too small for the filter to capture.

 

[DoubleWasp]

Oil may have better detergents and it's cleaning stuff out. Dark is not a problem as long as it doesn't look like glitter glue.

 

[CourierDriver]

Depends on the engine type possibly, blow-by by pistons,leaky valve seals, fuel mixture stuff, bad gaskets in engine, existing engine gummed up, and on and on. Diesel get black usually quick.
The above data is just my opinions.

 

[147_Grain]

Also, one oil brand might cleanup the contaminant residue leftover from another brand - quickly turning the oil darker than normal as it cleans.

 

[mpersell]

Short trips in winter driving due to richer mixture, dirty air filters, etc.

 

[Doog]

Mobil1 always gets dark in my cars at 1500 miles...but I am a short tripper with a 2 mile commute.

 

[Chris142]

Filters don't get loaded under normal circumstances.

 

[sicko]

It also depends on the additives. Some additives will darken when exposed to heat and therefore darken the oil. Some people mistakenly think that the appearance of the oil indicates how much it's cleaning or how much life is left in the oil. That's not necessarily the case because some additives might darken very quickly, though they continue to last for a very long time. While other oils might use different additives that don't darken.

Don't get me wrong, if an oil is thick and dark as night, I'm not going to tell someone to keep it in the engine b/c it might just be the additives. Obviously common sense needs to be applied.

 

[cmhj]

Originally Posted By: CourierDriver
Depends on the engine type possibly, blow-by by pistons,leaky valve seals, fuel mixture stuff, bad gaskets in engine, existing engine gummed up, and on and on. Diesel get black usually quick.
The above data is just my opinions.


Sometimes perception is the truth.

 

[Corvette Owner]

My cars with iron blocks and aluminum heads tended to turn oil black. My Corvette with aluminum block and heads keeps the oil golden the entire OCI.

 

[Shannow]

Originally Posted By: aa1986
I've read a few times that some people have oil that will turn from clean to dark at x,xxx miles every oci.

This has always intrigued me so thought I'd ask for theories on why this occurs.

I personally thought it could be due to the filter getting loaded enough that it begins to bypass at a particular mileage and that this is a repeatable occurrence. But I understand that such a reason doesn't stand up to the fact that some soot particles are too small for the filter to capture.


My Diesel Nissan stays clean for 6,000km or so, darkens a little, then around 7,500km, goes instantly "dark", and uses just under a litre...top up and drive to 10,000.

My Caprice literally changes colour in a day....when I'm playing thermocouple down the dipstick for oil temperatures, I've got the dipstick out most days, and can see it change.

My theory (see my varnish removal threads) was that this was the point that the oil had become saturated with varnish, and thus the colour change...I'd change it straight after that point for a couple of OCIs (no difference in my varnish).

I still think it's at the point where something loses it's solubility, maybe varnish...but can't say for sure.

 

[aa1986]

Interesting Shannow. Thanks.