Oil colour - Primera_p
When the colour of engine oil changes from clear to brown does that mean it\'s absorbed as much muck as possible?

The reason I ask is that I change my oil & filter regularly - every 5k to be specific. I rarely use the car for short-distance

My oil changes to brown within a matter of weeks of the change!

Any ideas why this is the case??
Oil colour - borasport20
no, it just means the oil is doing its job and scavenging all the muck.

now when it turns black and treacly...

I have to grow old - but I don't have to grow up
Oil colour - 3500S
A golden brown colour for a petrol car is absolutely fine. As borasport says, when it's black it's time to think of a change.
Oil colour - Cliff Pope
Surely it's what you can't see that does the damage, not the micro-fine colouring? Dissolved acids eating at bearings, water causing corrosion, petrol thinning the oil and reducing its lubricating properties, corrosion inhibitors losing their power through heat or age, etc?
Oil colour - Primera_p

Could you elaborate on that for me a little?

Oil colour - Cliff Pope
Could you elaborate on that for me a little?

Well, I thought I had said it really. The black colour, in moderation, comes from very fine soot particles which clearly aren't trapped by the filter and so presumably do no harm.
But when an engine is running cold the oil becomes the receptacle for all sorts of undesirable dissolved things - neat petrol from the rich starting mixture in the cylinders, corrosive blow-by exhaust gas, condensation from damp air in the crankcase. A lot of these are evaporated on a long run (hence long run good, short run bad) but residues will remain to attack bearings and valve gear.
Also oil contains a mixture of corrosion inhibitors, additives to withstand extreme pressure and heat, and doubtless other things too. These I understand gradually break down or lose efficiency with age, hence the importance of changing the oil frequently.
None of this is visible, although the smell does give a bit of a clue.
Oil colour - Andrew-T
Cliff - to add to your list of bad things happening in engines: oil consists largely of medium-chain hydrocarbon molecules (like diesel fuel, only longer so they are not volatile enough to burn). Very gradually they get minced by the engine, so their lubricating property decreases while volatility increases. Just another reason not to wait too long before changing your oil instead of simply topping up.
Oil colour - OldOiler
Another tip change your oil before your MOT also - lowers the particulate values, we have to do this on our Cummin's loco engines.
Oil colour - pmh
Lowers particulate emmisions? What are Cummins loco engines? diesels? I didnt know trains require an MOT?

Well known tip for marginal MoT petrol engines is to change the oil, presumably oil gets contaminated with petrol and results in richer mixture via breather system. I have a feeling that same applies to HC readings.

Any definitive answers out there?

pmh (was peter)
Oil colour - glowplug
I think theres been lots said in previous postings about oil colour, generally about changing from normal to synthetic and how this can purge the engine of long term build up with the effect of dis-colouring the oil within days.

Try this site for more oil/additive info -


Oil colour - OldOiler
I'm affraid the new trains HAVE to meet certain environmentle standards - and our fines are expensive!!
Yes Cummins are diesel units - big diesel units 350ltr oil changes every 9k
Oil colour - smokie
"diesel units 350ltr oil changes every 9k"

A fast-fit chain do Mobil 1 for £34, although you need to get the vehicle to them... :-)
Oil colour - bafta
I'd love to see their faces. 350 litres for £34. Magic!
Oil colour - Wooster
Just a thought... Try an engine oil flush. If the engine has been run for excessive time between oil changes, there can be excessive soot and muck retained by the engine - it won't all come out when the hot oil runs out of the sump plug hole. I had this on my s/h Corolla. Oil went very dark with 1000 miles. Used engine flush (Wynns, I think) and now the oil stays a sort of new, gold colour for 4000 miles.

Value my car