Astra Diesel, oil changed or not?

[Glosphil]

Hiya, one of my other cars, an Astra Diesel has just had an MOT and oil/filter change. When I pull the dipstick out, the oil is dark and almost black in colour, this to me would suggest its not been changed, but I could be wrong. How can you tell ?

Also, cant find the oil filter? any ideas? Is an Astra G 2.0 Turbo Diesel DI

[Ric]

diesel oil turns black almost after 5-10 minutes, dont know why my works van did the same

[Graham S]

Diesels normally look dark after an oil change, normally i've noticed instead of looking black when its dirty, diesels tend to go a more dark grey colour as if its sooty, if you get what I mean?

[Glosphil]

Ah, phew, just as well I didnt go and moan then :)

I checked my porsche dipstick, thats not been serviced for a year, and thats still pretty clear, so assumed the worst.

[edge]

Sometimes you can tell by having a sniff.
Becareful where you put your nose :lol:

[Glosphil]

Yeah I did that, smelled like petrol, and slightly burnt.

[mk47]

Yeah I did that, smelled like petrol, and slightly burnt.

That was your fingers :p

[Glosphil]

Shut up bitch :P and get me a price on that power cable you copy cat

[Kranz]

The only way you can tell is by analysing the oil. Costs between £13 and £25 depending where you go ;)

Diesel oil gets VERY contaminated by soot, which is a byproduct of the combustion. Diesels produce a lot of soot and have very high combustion pressures, so a bit of this soot goes past the piston rings into the crank case and is absorbed by the oil. Over only a couple of hundred miles this will make new oil look very black.

A petrol engine produces virtually no soot, and the combustion pressures are lower = virtually no soot in oil = looks clean for ages.

There is a difference berween diesel & petrol oils for this reason. Diesel oils have much stronger dispersants and detergents to hold the soot in suspension and neutralise any harmful effects from it. Petrol engines don't like these high levels of dispersants and detergents, and they may harm the 02 sensor, so only use diesel oil in an emergency.

An engine retains about 10% of its total oil volume as oil hangup... that means its trapped in places that it can't drain from. An oil flush will get it out by diluting the oil that remains after a drain with new oil, but 10% of the new oil plus old oil will remain. After draining the flushing oil out 1% of the original dirty oil will remain!

So, if you change the oil on a diesel you'll have 10% of the very dirty black stuff hanging around in places, but not in the sump.
You check the oil level & its ok and looks clean. You start the car and check it again and its instantly black!!!