Oil Colour after Service

[DarrenW]

Hi All,

I'm a Mercedes newbie - so forgive me if this is a stupid question for my first post!!

I recently purchased a fantastic ML270 Cdi. 53 reg with only 19,000 miles on the clock. It's absolutely fantastic - and with the Lux pack, Family pax a Parktronic knocks spots of the alternative which was a nearly new Ford S-Max!

It was however due a major service (only it's second ever - the first being done approx 2 years ago at 9,500 miles). I had a major service done at a local MB dealership for the nice old price of £550 !!

However, after cleaning the car at the weekend I happened to check the oil level. The oil on the dipstick looks like it hasn't been changed. It's a black colour rather than the golden brown the I'm used to for new oil - however this is also my first diesel car - so wanted to check if diesel oil is a different colour to 'petrol' oil?

If anyone could advise that would be great.
Cheers
Darren

 

[rf065]

New oil in diesels turns black very quickly, unlike petrol engines.
How long or how many miles after the service did you check it.
If it was a couple of weeks and a few hundred miles or so, probably normal, if it was the same day, I'd worry it had not been done.

Russ

 

[DarrenW]

Thanks for the quick reply - I had the service done on the Tuesday and I checked the oil on the Sunday - probably covering about 110 miles since the service.

Unfortunately it does mainly short journeys as well so do know if that will make any difference.

Probably just me being paranoid - just never trust dealerships. For a start the service was actually LESS than the price they quoted me - which made me think they hadn't done everything they were supposed to (fuel filters, air filters etc) - but they assured me they had (even though they had hardly filled out the service book correctly!)

I know I should probably take it to a good independant - but this was only it's second service, and I'm new to Mercedes so wasn't sure how much the resale would be harmed from not having the coverted 'FMBSH'!!

Cheers
Darren

 

[Old Hat Shop]

Hi Darren, I see a lot of diesel engined forklifts in my work and have only seen clean oil in one example. it had been serviced and never moved since.

Your example sounds quite normal given the figures you state.

Hi All,

I'm a Mercedes newbie - so forgive me if this is a stupid question for my first post!!

and don't apologize, you'll post a lot more stupid questions before you're done. We all have.

 

[wireman]

Your situation is quite normal, the black is soot scrapped from the cylinder walls by the pistons, a petrol engine does not produce anywhere near as much soot as diesel so it often surprises new diesel owners.
I have the dubious honour of owning a rover 25SLD as my emergency/let her indoors have a drive car, it has a direct injection + turbo engine which is run on 10/40 semi synthetic oil changed at 8000 instead of the 12000 advised, the new oil goes black as soon as the engine has been started. If the oil is changed without the filter (cheap oil) and then again (decent oil) with a new filter after 100 miles the second oil change does not begin to discolour for about 1500 miles.
My 124 250D (indirect injection) makes the new oil black either way.

 

[FIBAMAN]

Your oil would probably turn black on the run home. There will always be some residual oil trapped in various parts of the engine. As Wireman says, the black is carbon, which, incidentally, is used as a pigment for allsorts of things and is extremely effective, so it dont take much to colour up your oil. With regard to short runs, well they are not really any good for any engine,, however your diesel should run a bit hotter than a petrol, so you may get a little longer out of your exhaust, having said that diesel fuels have more sulphur so you need to run with good quality oils to neutralise any sulphuric acid that could be generated.
Maybe Oilman can give you a few tips. (At least he knows what he is talkin about).

 

[rf065]

however your diesel should run a bit hotter than a petrol,

Diesels are more efficient than petrol engines, less energy is turned to heat, that is why they run cooler than petrol engines and return more MPG.

Russ

 

[FIBAMAN]

Diesels are more efficient than petrol engines, less energy is turned to heat, that is why they run cooler than petrol engines and return more MPG.

Russ

I dont understand your logic. Diesel requires a much higher temperature to self ignite the atomised fuel (v. high compression ratio compared to petrol engines), that is why diesels do not have spark plugs, petrol vapour ignites at much lower temperatures with the ignition being by way of a spark. The calorific value is greater in diesel than in petrol also. Much of the difference in efficiency is down to fuel metering accuracy and and completeness of burn.

 

[Aussie Nick]

I think I have to go along with rf 065's first post. I think it is a little too early for the oil to be turning black. I can understand some discolouration in the 100 miles and five days but it should not be a dark black colour so soon. I agree with Fibaman"s previous post to this however about higher compression ratio etc.

 

[rf065]

I dont understand your logic. Diesel requires a much higher temperature to self ignite the atomised fuel (v. high compression ratio compared to petrol engines), that is why diesels do not have spark plugs, petrol vapour ignites at much lower temperatures with the ignition being by way of a spark. The calorific value is greater in diesel than in petrol also. Much of the difference in efficiency is down to fuel metering accuracy and and completeness of burn.

A diesel engine produces very little heat compared to a petrol engine.
Thats why they are sometimes equipped with auxiliary heating systems or electric heaters to supply hot air to the heating system as the engine itself cannot supply enough heat unless running for a long time at higher revs. Petrol engines are less efficient and produce far more heat. That is not my logic, but fact.

Russ

 

[wireman]

Diesel will spontaneously combust at around 300C, petrol about 330-380C depending on octane and summer/winter mixture. Its because of the lower temperature of ignition that gasoil (diesel) is used as the fuel in compression ignition engines. This is also why diesels with any significant amount petrol in their tanks are more difficult to start.
Due to the diesel being an excess air engine combustion temperatures are much lower than petrol engine temperatures, this lower temperature makes it easier to get most of the heat out of the burning charge and is the main contribution to the higher specific fuel efficiency of the diesel engine, it also contibutes to the soot not getting fully burnt and ending up mostly in the exhaust gasses but some inevitably gets into the oil and it gets very black.
I have been using diesels for the last 20 years and they all have dirtied their oil within seconds of starting up after an oil change, unless the engine is flushed as part of the oil change, I would not recomend flushing oil in modern engines since the small quantity left in the engine would dilute the realy decent modern oils we now use. Try putting a small quntity of used oil into a gallon of new and it goes sufficiently black to look like the old oil.

There is no problem with this coloration occuring, diesels have been used for some 80 years and if it was a problem somebody would have done something about it by now.
In my youth a secondary bypass oil filter system was introduced, I do not remember the brand but it could keep the oil new looking in large truck/plant engines right up to service time, what it could not do was keep the oils additives and improvers in good condition and saw few takers in comercial fleet use. A test vehicle at Leyland trucks showed no advantage from fitting this system over 250,000 miles of heavy usage.

Useless oil fact:- London transport used to supply used engine oil to Fleeet street as printing ink untill the health nazis thought it might hurt somebody and stopped it.

 

[Aussie Nick]

I believe we are detracting from the main issue posed by darren W. The real question is whether the dealer changed the oil. It is too difficult for anyone to say for certain what the dealer did. The discolouration can be explained by the 100 , or so miles travelled, especially when the diesel lubricating oil used is likely to have contained dispersants to clean the engine,, as most modern day diesel lubricating oils do.

The new member should have checked the dipstick on delivery after service, or very soon thereafter. At that point one could say with some accuracy whether the oil had been changed or not. However, that is now in the past and it is impossible to make an accurate assessment.

In future it would be worhwhile to check the oil immediately after service completion and at delivery or as soon as possible therafter.

 

[Ultymate]

I've just retired from a life as a mechanic and can assure you that fresh oil in a diesel engine will turn black in colour almost the instant you start the motor by the time you've run the engine stopped it to see if it needs topping up after filling the oil fiter when you check the dipstick the oil will be black

 

[FIBAMAN]

Diesel will spontaneously combust at around 300C, petrol about 330-380C depending on octane and summer/winter mixture. Its because of the lower temperature of ignition that gasoil (diesel) is used as the fuel in compression ignition engines. This is also why diesels with any significant amount petrol in their tanks are more difficult to start.
Due to the diesel being an excess air engine combustion temperatures are much lower than petrol engine temperatures, this lower temperature makes it easier to get most of the heat out of the burning charge and is the main contribution to the higher specific fuel efficiency of the diesel engine, it also contibutes to the soot not getting fully burnt and ending up mostly in the exhaust gasses but some inevitably gets into the oil and it gets very black.
I have been using diesels for the last 20 years and they all have dirtied their oil within seconds of starting up after an oil change, unless the engine is flushed as part of the oil change, I would not recomend flushing oil in modern engines since the small quantity left in the engine would dilute the realy decent modern oils we now use. Try putting a small quntity of used oil into a gallon of new and it goes sufficiently black to look like the old oil.

There is no problem with this coloration occuring, diesels have been used for some 80 years and if it was a problem somebody would have done something about it by now.
In my youth a secondary bypass oil filter system was introduced, I do not remember the brand but it could keep the oil new looking in large truck/plant engines right up to service time, what it could not do was keep the oils additives and improvers in good condition and saw few takers in comercial fleet use. A test vehicle at Leyland trucks showed no advantage from fitting this system over 250,000 miles of heavy usage.

Useless oil fact:- London transport used to supply used engine oil to Fleeet street as printing ink untill the health nazis thought it might hurt somebody and stopped it.

I bow to your greater knowledge and apologise to rft065 for questioning his logic.

In my experience my diesels have always warmed up more quickly, especially when running the heater in winter (got warm quicker than petrol).

 

[dolmen]

I've just retired from a life as a mechanic and can assure you that fresh oil in a diesel engine will turn black in colour almost the instant you start the motor by the time you've run the engine stopped it to see if it needs topping up after filling the oil fiter when you check the dipstick the oil will be black

I've seen this in my own car.

I like many others have concerns about servicing, I believe we either stand over the mechanic or show some trust. There's much more going on around us that we don't see or hear about and would probably annoy us too!

Cheers