Volvo S40 burning 1.5L of oil per 1000km

My first thought would be to check or replace the (PCV) Positive Crankcase Ventilation valve. This valve provides a vacuum to the lower crankcase to make the downward movement of the pistons smoother and also remove hydrocarbons from the oil and burn them through the combustion chambers. When this valve gets worn or contaminated the check valve inside will let oil pass and enter the intake manifold where it gets sucked in with the intake air.
The vacuum system on gasoline engines increases at idle and decreases with throttle application so the fact that it seems to burn oil when driving downhill when you are not touching the throttle seems to confirm this. Another factor that may add to the oil consumption is the hose or design of the PCV tubing. For instance if the system has the valve inserted into the valve cover then drops to a lower point before coming back up to connect with the intake it can create a valley where oil can pool until the vacuum level increases or the vehicle is facing a direction that allows the oil to drain from the area and suddenly enter the engine.

The valve stem seals can allow oil to be consumed but generally tend to cause blue grey smoke when the motor is started or after it is left idling for a while. You will generally notice a puff of smoke as the throttle is pressed pulling away from a stop. You mentioned black smoke in the post which is normally a sign of excessive fuel but could be from carbon build up in the exhaust system so I don’t think this is going to be the issue with oil consumption.

Lastly you will want to closely inspect the outside of the engine for any oil leakage. Sometimes the oil can leak and drip from somewhere that is not easy to locate. I have seen cars that had oil dripping from the bottom of the intake manifold onto the inner fender and traveling down to the mud flap so that it looked like the driver had driven through oil from another vehicle. But after looking closer it became apparent that the oil was coming from the PCV system and the hose had a small crack that was allowing oil to come out after the engine was shut off and the vacuum leaked out enough to allow the oil to seep out.

Hope this helps you out and keep us posted.

[quote=”JoshMc” post=34345]My first thought would be to check or replace the (PCV) Positive Crankcase Ventilation valve. This valve provides a vacuum to the lower crankcase to make the downward movement of the pistons smoother and also remove hydrocarbons from the oil and burn them through the combustion chambers. When this valve gets worn or contaminated the check valve inside will let oil pass and enter the intake manifold where it gets sucked in with the intake air.
The vacuum system on gasoline engines increases at idle and decreases with throttle application so the fact that it seems to burn oil when driving downhill when you are not touching the throttle seems to confirm this. Another factor that may add to the oil consumption is the hose or design of the PCV tubing. For instance if the system has the valve inserted into the valve cover then drops to a lower point before coming back up to connect with the intake it can create a valley where oil can pool until the vacuum level increases or the vehicle is facing a direction that allows the oil to drain from the area and suddenly enter the engine.

The valve stem seals can allow oil to be consumed but generally tend to cause blue grey smoke when the motor is started or after it is left idling for a while. You will generally notice a puff of smoke as the throttle is pressed pulling away from a stop. You mentioned black smoke in the post which is normally a sign of excessive fuel but could be from carbon build up in the exhaust system so I don’t think this is going to be the issue with oil consumption.

Lastly you will want to closely inspect the outside of the engine for any oil leakage. Sometimes the oil can leak and drip from somewhere that is not easy to locate. I have seen cars that had oil dripping from the bottom of the intake manifold onto the inner fender and traveling down to the mud flap so that it looked like the driver had driven through oil from another vehicle. But after looking closer it became apparent that the oil was coming from the PCV system and the hose had a small crack that was allowing oil to come out after the engine was shut off and the vacuum leaked out enough to allow the oil to seep out.

Hope this helps you out and keep us posted.[/quote]

+1 I don’t know if I could do much better than this. I was also thinking valve seals. Actually when you slow down and are at closed throttle. At that time intake vacuum goes to max and if you have valve seal problems it will show up during these times and you’ll notice smoke from the tail pipe. I suspect you have a valve seal issue and you might consider removing the valve cover and checking them.

The PCV is also a possibility.