Hey does anyone know why in some cars the oil goes black really quickly, while in others it stays clear for 7,000 kms or more?

Maybe high temps cause oil to go black? My engine has been rebuilt but it still goes black.
justin

Good question. My guess is #1 cause is overrich fuel mixture.

The B110 design also stores fumes in the engine when engine is off. B210 (at least in USA) uses a charcoal cannister to avoid this problem.

That makes sense, an over rich fuel mixture would produce excess carbon which would get washed down the bores and into the oil. Actually my engine was running rich due to a hole in the intercooler. It also follows that LPG vehicles have much cleaner oil due to less carbon deposits. problem solved!

Good question.
My Nissan Almera the oil stays cleaner than my wife's Volkswagen.
I must mention that the Almera is fuel injected and obviously controlled by computer and all the fancy stuff while the VW uses Kjet fuel injection. VW after 1000km it starts to become very dark.
The datto is also quite clean for a while and gradually becomes darker.

Oil colour can no longer be used as an indicater of oil condition. New conventional and synthetic oils have changed. They go blacker much earlier than they used to. Synthetic oil breaks down the carbon molecule to carry it (more harmlessly)thru the oil's entire volumn. (goes blacker sooner). Conventional oil carries the whole carbon molecule around, but seperates when sitting. (lite on top, dark towards the bottom/ lite colour on dipstick.
Crankcase ventilation also effects oil colour. The stock 1200, Positive Crankcase Ventilation system does a good job when working properly. Excessive crankcase gasses (unburn't hydrocarbons) are vented into the intake at the correct time, to be burned in the cylinders. On a stock or mild performance engine a stock PCV sytem works well to prevent excessive carbon buildup in the engine & engine oil, allowing it to appear cleaner longer.
Did you replace your pcv valve, & check all PCV hoses after your engine rebuild?
When you modify an engine for performance, the whole PCV thing often has to go by the wayside. A race or 'hot' street engine cannot use a PCV system. The crankcase pressures are much higher at higher revs so the stock PCV can't keep up. The system must be opened up into a catch can and become externally vented. You also need one of those cute little chrome filters for the 'in' side of the system.
If you are running your car on the street, and it is stock or mildly tuned, use the stock PCV system, it works well and has no effect on horsepower. If you have a hot engine (twin carbs/cam/extracters), and are constantly at high revs, you'll haveto use an open system. High revs, richer mixtures, less crankcase venting, higher temps, all = darker engine oil sooner.

thanks dave , good explanation

Thanks guys, actually my engine is a CA18DET- i cant' seem to find a pcv valve, only a direct feed via a restrictor to the air intake. I have seen a few engines with a direct breather to the atmosphere, but this is probably illegal i think.
justin

another reason not to vent oil gases into inlet is it lowers the octane rating therefore making your engine more prone to pinging if in the modified category