Should new oil look black on a diesel?

[Miss_B]

I've recently had my 2017 Ford Focus Tdci serviced and the oil looks black (I checked it having driven less than 10 miles) . Also the 'oil change required' warning started coming on just after the service, they told me they just forgot to take the light off. I've arranged to take it back in as the oil looks old to me, they've said they'll take a look but have told me oil in diesels turns black very quickly due to carbon build up. I've always driven petrols before is this correct that the oil would turn black within a few miles on a diesel?

[Super Slo Mo]

Yes. 10 miles seems quite soon, but it definitely doesn’t take long.

[guards red]

Depends on how they have drained it. If they have used a pump through the dipstick it will leave an amount that will turn the new stuff black.

Also if it has an oil cooler which would've retained some old oil.

[Miss_B]

OK thanks, is there any other way of knowing if they actually changed the oil?

[996TT02]

Yes, it is impossible to clean out the inside of an engine - as soon as you start it up the remaining oil will make the new oil go very dark near immediately. Not quite as black as before, but certainly no lovely shade of gold.

[Super Slo Mo]

Miss_B said:

OK thanks, is there any other way of knowing if they actually changed the oil?

You would have to get a sample analysed. There’s no easy way, although old oil does feel a bit different when rubbed between two fingers than new oil. It’s veey inconclusive though.
If it’s really bothering you, get it done again elsewhere. It’s not that pricey a job in isolation.

[Miss_B]

OK thanks, so it sounds like I don't need to take it back in. Does the oil change warning just come on after an amount of time rather than anything to do with the level/quality of the oil in the car?

[227bhp]

Yes it's quite normal on a diesel, the old oil is so black that what was left in colours the new.
It's quite possible on a petrol too if the oil hasn't been changed for a long time, I did one recently that was so. It annoyed me so I used the new oil as a flush and then changed it again, it was golden after that.

Edited by 227bhp on Tuesday 2nd October 13:52

[Super Slo Mo]

Miss_B said:

OK thanks, so it sounds like I don't need to take it back in. Does the oil change warning just come on after an amount of time rather than anything to do with the level/quality of the oil in the car?

It can’t tell you the quality of the oil. Some cars have an electronic dipstick though which monitors level.
Usually the service indicator either works to a pre-determined mileage or time period, or is based on how the car is driven.

[ninjag]

Miss_B said:

I've recently had my 2017 Ford Focus Tdci serviced and the oil looks black (I checked it having driven less than 10 miles) . Also the 'oil change required' warning started coming on just after the service, they told me they just forgot to take the light off. I've arranged to take it back in as the oil looks old to me, they've said they'll take a look but have told me oil in diesels turns black very quickly due to carbon build up. I've always driven petrols before is this correct that the oil would turn black within a few miles on a diesel?

You can test oil by putting a little bit on your finger and thumb and rubbing them together. It's hard to explain because it's just something you can feel, try it with some oil you know for sure is old then do the same thing with some brand new oil. You should be able to feel the difference.

EDIT: Sorry, I missed Super Slo Mo's post.

Edited by ninjag on Friday 5th October 09:43

[Rockster]

My experience with my 2002 VW Golf TDI is after 5K miles the oil would be as black as coal.

I'd do the change by the book: Run the engine to operating temperature. Drain the oil. Replace the filter. Fill the engine with new oil. Check the dipstick to ensure there was some oil in the engine. Oil looked reasonably fresh. Then start the engine and let it run a bit then shut the engine off and let it sit for a bit while I put tools away and cleaned up. Then after 10 or 15 minutes check the oil level again.

The oil on the dipstick was black as coal. Based on my experience with my first (and so far only) diesel, it really takes no time for the fresh oil to go black.

But this doesn't mean the service department didn't goof and the oil was not changed. (I took this same VW in to have tires rotated. Picked up the car and for because the tires didn't appear to have been rotated I popped off the hubcaps and looked at the lug nuts. Except the ones on one wheel which I had wrenched on to replace a flat tire all the other lug nuts on the other wheels were untouched. Still had the factory paint dabs. Took the car back after showing the service manager the untouched lug nuts the 2nd time got the tires rotated.)

As someone else suggested you can get some oil -- from the dipstick -- on your fingers and then compare the feel to fresh oil out of the bottle. Engine oil with any real miles on it will have a different feel.

Or you can obtain a sample of some oil from the engine and send the sample out for analysis and see what the report says. Fresh oil should have very good additive numbers, very low -- zero essentially -- PPM for everything else. TBN should be at the oil's out of the bottle number.