What causes engine oil to blacken so quickly

[bigjimmyauk]

Just curious my dad had a S reg vectra that had done 70k after a oil change every year the dip stick would still look a nice golden colour.

Now my zafira had done 40 odd K after a oil change the oil turns black within a couple off weeks.

What actually causes it to darken and why so quickly.

*edit* they are both 1.6 ecotec petrol engines

 

[Begbie]

Just curious my dad had a S reg vectra that had done 70k after a oil change every year the dip stick would still look a nice golden colour.

Now my zafira had done 40 odd K after a oil change the oil turns black within a couple off weeks.

What actually causes it to darken and why so quickly.

*edit* they are both 1.6 ecotec petrol engines

Is 40K book figure when the oil should be changed?

Seems like a lot of miles before they get changed?

 

[bigjimmyauk]

sorry my bad, i ment my oil gets changed every year, i was just stating it's done 40 k but the oil blackens within a week or two after a oil change.

i was just curious why my car does this so quickly, but my dads car could go an entire year and at oil change time the oil would still be a golden colour.

 

[jumpy]

Carbon/soot/engine dirt as part of combustion process iirc - the oil not only lubricates moving parts, but helps clean the engine internals too keeping those combustion by-products in suspension in the oil instead of collecting in the engine. It's why turbo charged engines have (usually) a shorter oil change period; as the oil gets dirtier, it looses some of its lubricity, which is a bad thing for a turbo as the turbine/compressor shaft usually floats on a film of oil.

I guess the difference between yours and your dads car could be anything from how well it's been looked after in the past, how hard you drive it, how many short to long journeys you do, tuning/condition/age/miles/wear of the engine, type of oil used.

Could also be new oil from a change flushes out some dirt that remains behind in the sump from the old oil, which would explain why it gets dirty so fast. Maybe change your oil once every 6 months instead?

Who knows. My landrover oil stays nice for a month or so, but every time I change it (2 times a year) it's always black. It is a diesel though.

 

[adam cool dude]

Try doing a oil change in the next 500 miles than again in the next 1000 miles. It helps clean the engine out. A lot better than using a engine flush which does more harm than good. Especially on high miles.

 

[DAnDan]

Just because it's black doesn't mean it's reached the end of its life. The soot buildup will cause the colour to change far quicker than the useful life of the oil is depleted.

 

[jumpy]

^^
true.

Try doing a oil change in the next 500 miles than again in the next 1000 miles. It helps clean the engine out. A lot better than using a engine flush which does more harm than good. Especially on high miles.

Yer, can knacker seals. Over time some of the seals and gaskets sort of get oil absorbed into them (cork/paper/older rubber seals) the harsh cleaners in the engine flush can cause these seals to disintegrate - that's what I was told anyway. Regular oil changes, with a quality full/semi synthetic or mineral oil will always be better than a long service interval and engine flush.

I use mineral oil in mine and do a filter/oil change once every 6 months or so, sometimes a little longer if I've not done many miles.

 

[Matt82]

depends how "clean" the engine is inside to start with ie does one have loads of deposits already in there

the breather system makes a big difference too. i ran an angine with the breather ventint to atmosphere and the oil blackened faster.

my old 16v, on 235k miles, the engine oil stays clear/gold for 3k miles easily.

on the 1.8t, its very dark within 1k miles. the 1.8t isnt totally clean inside

 

[Simon]

Diesel's will go black pretty much instantly.

Petrols will depend on combusition, ideally you want dirt in the oil rather than the engine though so oil going black is not a bad thing

 

[acemastr]

Make sure the oil filter was changed.