Did they change the Oil ?

16 Sep 2007
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United Kingdom

I recently purchased a used Diesel car from my local garage, the car is low emission and uses fully synthetic oil. According to the garage it was serviced before being delivered to me, and the log book has been stamped by them to show the next service is due in 20,000 miles.

I checked the oil yesterday and on the dipstick it is a dirty black colour. I've only done 200 miles since receiving this car, therefore does that mean they have skipped the oil change during the service?

I've only owned petrol cars before, and certainly in my experience after 200 miles the oil would still be clear. But since this is a diesel engine would this still be true?

Thanks for your advice
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'Serviced' can mean almost anything.....but it's most unlikely that the garage would change the oil unless it was actually due......'checked over' is probably a more realistic term.
Diesels do blacken their oil much more quickly than petrol engines......after just a few miles, the oil can be black again.
Which vehicle, and what mileage do we have here?
John :)
Generally, diesels will dirty their oil MUCH more quickly than petrol engines. On top of that, some cars have better designed oil sumps than others. it's not always possible to get every drop of old oil out of them when you change the oil and you don't need much oil to make the new stuff look black. A far better indication (if it has a visible one) would be to look at the oil filter. These must always be changed when the oil is changed. Some are internal, so you won't be able to check. Most, however, are external and look like a cylindrical metal canister, about the size of a fizzy drinks can, screwed on to the side or bottom of the engine somewhere. If that looks new, it's a fair indication that the job has been done properly.

If you post what sort of car, engine size and age, maybe someone on here will be familiar with the model and know what sort of filter it's supposed to have and where it is.
If the oil was particularly filthy (20k miles is a long service interval, I'd expect the oil to be horrendous by that point) then the sludge stays behind and gets mixed into the next batch of oil.

Oil change intervals are a compromise between the engineers who want short intervals and the marketers who want long intervals. 20k is a lot to ask from 5L of oil, especially if it is a turbo, every 8-10k is more reasonable and there is nothing stopping you swapping your own oil mid way through a service interval.
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Thanks for your replies.

The vehicle is a Citroen Nemo Multispace 1.4L diesel.

The logbook has been stamped by the garage to say the next service is due in 20,000 miles. The last service in the book was carried out 10,000 miles ago.

Therefore if I ignore this potential problem, by the time of the next service the oil could be well past it's lifetime. Unfortunately the oil filter is not a metal cartridge type and easy to inspect, it is a paper element with a plastic cover that needs a special tool to unscrew it.

The only other curiosity is that next to their entry in the service record the garage has written and circled the letter 'A'. This hasn't been done anywhere else in the book, do you know what that means please?
Basically that's a small or minor service......items such as the brakes are just inspected, rather than stripped out and cleaned.
The oil needs to be changed at 10k miles (or yearly) .....some would say sooner but with the quality of oil these days that's ok. Longer intervals mean trouble, especially for turbochargers.
Oil changes are simple enough to do.....usually the euro filters are beneath a plastic cap with a hexagon top.
John :)
OK, thanks

If I can't persuade the garage to change the oil, I would be prepared to do that myself, since I have done numerous times before on other cars but all with metal cartridge filters.

It says on some internet sites that you need a special tool to undo the hexagonal filter cover to avoid damaging the plastic, is that strictly true or can you use a normal socket spanner?

Just a normal socket and extension will do - if you have one big enough!
The new filter comes with a new O rings as required.
The plastic caps aren't that tight - or shouldn't be!
John :)
Ask them did they change the oil before you got the car? Most now suck the oil out the dipstick pipe and don't lift every last drop, so it colours the new oil quite quickly.
Don't go changing the oil yourself until out of warranty ..........

Sometimes they let apprentices do the service and he/she just might have took the suction pipe out a bit quick as they are probably given a set time to get everything done. So no real harm done, just a bit of discoloured oil.

If you are still unhappy ask them for a price to change oil and filter ........
We was always brought up to change oil every 6 months with diesels - yes I know mfrs say 12 months now with the high-quality synthetics.

But if you do it yourself, 6 months can only do good, and gives you a chance to see if everything's OK down under.

I do this with my L/Rover Td5 which I've had 10 years and it's never missed a beat.
I used to change mine every 5000 miles on the XUD engines, the Hdi's are cleaner burning but I still change mine at 8000. On the 1.6 Hdi oil sludge is responsible for repeated turbo failures, the 1.4 is better but I wouldn't risk 20k on an oil change.

Same as above, never leave it to 20k, always change oil every 10k, just oil and filter would do.

Diesel oil will turn black within an hour, however it will still be thin and runny, if its black tar/sludge like then its not been changed in years.
I used to change mine every 5000 miles on the XUD engines, the Hdi's are cleaner burning but I still change mine at 8000. On the 1.6 Hdi oil sludge is responsible for repeated turbo failures, the 1.4 is better but I wouldn't risk 20k on an oil change.


Just been down and got the bits to do mine (at about 8000) probably do it next week now.

I've linked to this before, but it's worth knowing.
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