My bmw 316i is burning oil needs top up after few weeks..jus had service and has a burning oil smell. there is no smoke from exhaust but i notice a black substance in exhaust

hi
White smoke is burning engine oil.
mostly when Engine oil is changed or topped up
little oil get dropped and when engine heats up. it burns the oil.
but once oil is burnt then no more smoke is there.

unless you have a leak
thanks

Are you sure the oil is not leaking, instead of being burned? Also, are you absolutely certain the oil was being added to the correct place and was/is being checked correctly? If you were burning that much oil you most definitely should have noticed smoking exhaust and probably smelled it as well.

A leak of some fluid, probably oil, dripping onto the exhaust. This smells terrible, and it only needs a drop or two.

white were? the exhaust tip, or other spot, long pipe, name spot?
white, is steam or OIL.
oil smells like burnt oil and takes for ever to dispate
steam is water, and smells , sweet due to 50% glycol inside.
and goes away fast.
but all Gas engines make water at all the time running as a by product of combustion and for sure on cold days, some times full time cold
due to climate effects.
does your neighbors car smoke at same time, (look)
bingo , dew point.

all gas engine smoke cold started, (steam)

so first find out what it is,
take the dip stick out of a hot engine. stalled, drip it on the exhaust
see that smoke ,smell it? that is burning oil
now you know what you have, steam or oil. smoke.

white smoke is a water leak on the cyl head , blue smoke is burning oil , black smoke is over fuel or a blokage in air intake or exhaust ! is it smelling ike steam or oil or fuel out of the exhaust ?

Could the smoke be coming from the exhaust manifold on the passenger side of the engine? When the valve cover starts to leak, it is common for the oil to leak down and burn on the outside of the exhaust manifold.
Replacing a valve cover gasket is not difficult or expensive, and it is common for BMW valve cover gaskets to get brittle and shrink and start leaking every 10 years or so. My wife's 330 needed a new valve cover gasket at 6 years.

It's probably OK to drive. I imagine they failed to get the oil filter properly seated and you're getting a little leak there. DO BE SURE to check the oil level before you drive it and add if necessary.

Let an auto tech look at it because one way or the other it's going to end up on some tech's hands. Burning oil smell must be from the valve cover leak and dripping on top of the hot exhaust manifold burning it. The only time I smelled burning metal odor was from a smelting plant. It had an acidic smell that going to put you in tears.

You have a bad head gasket. You are leaking coolant into the engine block through the cylinders. This is why you have white smoke, and the extra coolant that doesnt get burned off is going into your oil.

It is not unusual for an older truck to be burning a little oil. It is burning very little so you will not smell burnt oil or see blue smoke in the exhaust. But the oil burn does add up and you may notice a drop on the oil dipstick after a few weeks. On a 9 year old truck under normal working conditions will burn a little oil. If you are having to add 1 liter between oil changes, that is ok, just shows normal engine ware. 2 Liters is acceptable between oil changes if the truck does a lot of heavy pulling or work. 3 or more liters indecates a problem, but at that rate, you should be able to smell oil and see blue smoke.