shamrode

As most of us are aware our 6.2 liter beasts (burn) consume oil. I presume everyone has a different consumption amount. My girl burns about 300 ml per 1000 km. Is consumption a direct ratio to the hardness we drive our cars? Also; when our cars burn oil, will we smell it in the cabin if there is no leakage? I smell burnt oil at WOT on hot days. Can anyone nail this for me?

m a x i m u s

Driving harder will burn more oil. Can't speak to the smell tho.

HBC350

My car smells like hot fluid inside the cabin after spirited driving. Doesn't smell like engine oil, though. Smells more like hot tranny fluid to me.

I have to add about a quart of engine oil every 5k miles, which is ok IMHO. Not ideal, but ok.

Diabolis

It also depends on the oil viscosity and - what you're alluding to here - the health of your engine.

During normal use you'd burn most of it as startup when the engine is cold and the tolerances are the highest. If you're using M1 0W-40, you'd burn about three times as much as you would with a 5W-40, and 1L per 2500-3000 km is perfectly normal for M1 0W-40 in a healthy M156 engine.

With a 5W-40, the oil consumption in a healthy engine should drop to somewhere between half and a third of that, so 1L per 6000-9000 km. I ran the MB 229.5 oil after having the enhanced cooling package installed on my car this summer (didn't feel like wasting 12L of perfectly good fresh sythetic oil and besides wanted to do some UOAs on it), and even after six punishing track days with 3+ hours of actual lapping time on each day in S+ (so prety much above 6K RPM the entire time), I don't think I was down more than 1L at the most over the entire summer. Am about to change the oil back to M1 0W-40 before the winter, but in terms of consumption those are realistic figures for a healthy engine - one liter per ~2500 km if you're runnign 0W-40, and well over 6000 km if you're runnning 5W-40.

I don't know what oil you're using or anythign else about your car (year of production, mileage, aftermarket tune etc.), but what would concern me in your case is the burnt oil smell in the cabin at WOT. I used to get that in my 4.2L V8 Audi S4 with scored cylinder walls, but that's irrelevant except for the fact that it was at WOT when a healthy engine shouldn't burn *that* much oil. If you can smell it in the cabin, you're burning more than you should, so chances are something is not sealing properly and allowing it to get in your combustion chamber. It's unlikely that it is piston rings or the block itself in an M156 motor, so the primary suspect would be the cylinder heads.


P.S. Can you get someone to drive behind you and see if they can see blue smoke coming out of your tailpipes when you step on the loud pedal?

shamrode

I have a 2009 with 100k km. Car burns around 750 ml per 1000 km (Castrol 5w-40.) I think this is normal?! The engine head was replaced 25k ago (bolt failure.)

BLKROKT

I think that's a little on the high side, but with that many miles it's to be expected. My car burns off almost nothing. I get about 1/8 cup in my catch can every 5k miles, and don't usually have to add any oil between changes although mine are much more frequent.

350Zed

When I park my car after giving her a bit of the stick, she smokes a bit from under the hood, and smells like burnt oil.

I did find a leaky valve cover gasket that was causing oil to leak out and burn on the block. I had the offending gasket replaced but I'm still getting that burning oil/lubricant smell, so I'm thinking another leak might exist somewhere.

You might want to get yours on a hoist and give her a thorough look-over for oil leaks from bad gaskets.

Diabolis

Shamrode - that's still on the high side even for a 100K km car, especially considering that you can smell it in the cabin at WOT after the engine has fully warmed up.

The Castrol Syntec 5W-40 is IMHO quite low on the peckign order and does tend to thin out a fair bit over time - I ran that in both Audis during their in-warranty years and did UOAs at every change. 100C viscosity was in the low to mid 10s after about 9,000 km - it should have stayed at *at least* 12 cSt. It's made from hydrocracked group III base stock, so the hot viscosity deteriorates over time down to a low 30-grade - but even assuming that you only change it once a year and it deteriorates to a 5W-30 (which can't be the case here as you're essentially continuously replacing the oil and thus doing a complete "change" every 12,666 km due to your burn-off rate), I'd still expect that at most you'd use a liter every 2500 km.

Seeing as your car is well past the waranty period and furthermore you are burning oil so M1 0W-40 may not be the best choise for that reason, I'd try (gulp...) running an unapproved, premium quality oil like the HDEO Shell Rotella T6. It's a 5W-40, VOA shows a HTHS of 4.5 and ~1400 ppm Zinc, and UOAs show the hot viscosity stable around 13 cSt even after 15,000 km with enough additives / TBN remaining. Alternatively, you can go with something like Liqui Moly Synthoil High Tech 5W-40 (also a decent full synthetic but AFAIK also 229.5 unapproved), or the 229.5 approved Leichtlauf High Tech 5W-40 (which is a "synthetic technology" blend - a little more environmentally and fuel efficient but not the ultimate in engine protection) or the MB-branded, Shell-made "MB 229.5" oil from your MB dealer. The Castrol is only making the problem worse - but it's NOT what is causing it. You do have too much oil getting into your combustion chamber because of a mechanical problem.

shamrode

Thank you very much for the reply. What an amazing world of information you have. Could you please explain to me what you said in layman's terms? If I understand correctly you are saying that I should go to a lower grade oil which protects the engine less but also burns less oil. What would be the normal amount of oil consumption for my car? The interesting thing is that I only smell the odor when it is around 25 degrees Celsius or higher. Today it was approximately 20 degrees and I smelled nothing while running the engine very hard. Is it possible that I could smell burning oil in the cabin with the windows up? If so then why do I only smell it when it is hot outside? Thanks again I've been following your posts for a long time and you always have great information that we all can learn from.

Khan 55

You know, you say the smell was there and you found a leaking valve cover? You repaired it but the smell is still there and only upon higher temp do you smell it really. My guess is due to the oil burning previously which you repaired the odour has soaked itself into the cabin filter.


I had a blow out on a primary cat on my 55 and damn it was like onions in the cabin if I drove it pass 5000rpm or for long distance. Repaired the cat but the odour lingered. I changed the cabin filter located above the battery on my 55 and...hey what do you know, the smell is now gone.
Maybe all you need is new cabin filters.

shamrode

Switched the cabin filter to no avail. Even if the car is burning oil why should I smell it from the inside?

Diabolis

In layman's terms - (1) you have an engine problem, and (2) you're IMHO using a mediocre oil. You could switch to a better oil and as a result you may burn a little less, but it won't fix the underlying problem with the engine.

As for why you can or can't smell it at any one particular time, your gusss is as good as mine. I could really smell it with the sunroof raised or fully open on my S4, but taking into account the relative position of the sunroof to the tailpipes and the fact that I'd be moving forward at a decent clip, what low pressure zones and aerodynamic verteces the car created whereby it would suck in some of the exhaust in the cabin (in my case never through the ventilation system or for that matter open windows - only the sunroof) is beyond me. I am sure Adrian Newey could perfectly model the airflow for us, but unfortunately he's not taking my calls these days...

solekeeper

i have never had to top up my car in 5k of owning it.

i guess my m156 was built to the T. i should find that guy and give him a call to thank him

shamrode

Might be a dumb question. What would you say burnt oil smells like? When oil is burning the engine bay doesn't produce fumes that are smelled in the cabin? The major fumage smelled is from the exhaust tips?

Diabolis

Diabolis

Sorry - couldn't resist.

Well... it smells like burnt motor oil. Trying to describe a smell is like trying to describe a taste or a color.

Whether the fumes are coming out of your engine bay is a different question altogether. If you have an exhaust leak where the headers connect to the block, it is possible that it may come out under the hood... it is extremely unlikely though. Unless you can see flames coming from under your hood (in which case you have a bigger problem in the form of an engine fire), it usually makes it's way through the tailpipes...

shamrode

Haha. I wish it smelled like perfume. If the fumes are making their way out of the tailpipe and I'm driving and leaving the fumes behind how would the fumes be entering the car? If not through the engine bay and all windows are closed how is it possible?

Diabolis

Your ventilation system. As I said, it all depends on how the air flows around the car - and yes, some of it may find its way back forward... at least it did on my Audi.

Do you still smell it when you set the HVAC to recirculate the cabin air?

shamrode

[QUOTE=Diabolis;6602467]Your ventilation system. As I said, it all depends on how the air flows around the car - and yes, some of it may find its way back forward... at least it did on my Audi.

Do you still smell it when you set the HVAC to recirculate the cabin

It's been too hot to try to see if I smell it with the air conditioner off. But I do smell it whether the air is recirculating or not. I thought maybe the recirculating air flap was not closing all the way.