Is there excessive consumption of engine oil?

[Anderson]

My 2008 9-5 Aero has traveled 280000 kilometers (approximately 175000 miles). I was preparing to travel a long distance, so I asked the technician to investigate the condition of the vehicle. I found that my engine oil is about 450-500ml less than the last maintenance, and it has been 5 months since the last maintenance and I have driven about 4500 kilometers.
The technician said that the engine oil consumption is acceptable, but I still can't make up my mind and would like to consult with the experts.
By the way, the engine has always been in good maintenance condition, using Mobil advanced fully synthetic oil and using RON 98 fuel throughout the entire process. There is a lot of driving in the city.
thanks

[silver2u]

if your engine previously did not use/loose oil between service intervals, and now it is 450 ml low, then something new is happening. the cause might be something minor (initially) that is still easy to remedy, or might be an early sign of something more serious (failing turbo charger seals, or piston rings for ex ?)

since you have not mentioned leaking oil, the oil is likely burned by the engine and expelled by the exhaust.

first step would be to check your PCV system is still functioning correctly (if your mechanic is not a saab expert he might not have done replacement of some inexpensive service parts for it). your many city driving trips would become an issue for a defective pcv system causing higher oil consumption.

you can do the "glove test" yourself very easily to have an initial indication if the PCV system is still healthy (do saab forum search). make sure you use warm engine at idle, then remove dipstick and attach glove to filler tube, and observe if glove inflates (bad) or if glove deflates and aspiration from negative crankcase is present (good )

[Anderson]

if your engine previously did not use/loose oil between service intervals, and now it is 450 ml low, then something new is happening. the cause might be something minor (initially) that is still easy to remedy, or might be an early sign of something more serious (failing turbo charger seals, or piston rings for ex ?)

since you have not mentioned leaking oil, the oil is likely burned by the engine and expelled by the exhaust.

first step would be to check your PCV system is still functioning correctly (if your mechanic is not a saab expert he might not have done replacement of some inexpensive service parts for it). your many city driving trips would become an issue for a defective pcv system causing higher oil consumption.

you can do the "glove test" yourself very easily to have an initial indication if the PCV system is still healthy (do saab forum search). make sure you use warm engine at idle, then remove dipstick and attach glove to filler tube, and observe if glove inflates (bad) or if glove deflates and aspiration from negative crankcase is present (good )

I have received your message. My PCV system was indeed repaired at the beginning of this year, and there was no oil consumption issue before that. Thank you for providing the ideas, they are very helpful

[silver2u]

Assuming your recent oil consumption issue is related to a newly defective PCV system .(and not some of the other more serious causes mentioned earlier)....

below is a diagram of the components of the PCV system on your 2008 car model

The most important PCV valve (often referred to as the "white PCV valve") is a small one-way valve that is an integrated part of PCV hose Nr 5 (that valve is marked RED in color on this illustration). on older saab models you could just buy the white valve separately and replace it, on 2004-2009 models this white valve is integrated on PCV hose 5 and is now one replacement part Nr item.

PCV Hose 5 goes from the "oil trap" box (marked Nr 4 ) that is located at the back of the engine near the firewall, and comes up to the valve cover area , and the small white valve at the end of hose/tube 5 then has another short PCV hose (Nr 6 on the diagram ) attached to it that then goes to the throttle body (marked TB )

this white PCV valve is known to go faulty and is best preventatively replaced at major service intervals (but most mechanics or service centers dont do this )

the purpose of this white valve is to allow your throttle body to evacuate and slightly aspirate crankcase gasses from the engine when it is at idle and your car is stationary, preventing crankcase pressure from building up pressure.
- the valve opens with minimal pressure of air flow towards the throttle body, and completely closes when air/gas pressure tries to flow in the opposite direction ( when your engine is increasing revs and accelerating for ex)

you can get increased oil consumption if:
1) the white valve is defective and then causes increased crankcase pressure. this white valve is a very sensitive pneumatic valve (eg for air and gasses) that opens at VERY low pressure (this light pressure is for ex similar to you exhaling air from your lungs without any added effort )
2) if a new PCV white replacement valve is incorrectly placed the wrong way around (it is unidirectional, and should only allow air/gasses to flow TOWARDS the throttle body !), it will completely block airflow in the intended direction !.
- if hose 5 (on diagram) was replaced with an OEM saab part, it is now not possible to install the valve incorrectly (because it is integrated into the hose 5 ). but if just the valve was replaced by an amateur, it is possible they placed it the wrong way around !
3) if an incorrect replacement white valve was used with the WRONG specifications. many online retailers now sell a metallic fuel system valve (cheaply) that some people are installing to replace this white PCV valve (because the plastic stems after a few years can become brittle from high heat exposure and then break or crack ) , but this metallic fuel valve is hydraulic valve valve with very different specifications that only opens at a much higher WRONG pressure and so still blocks airflow towards the throttle body.
note: PROPARTS, a non-oem cheap aftermarkets manufacturer of saab replacement parts (but they promote themselves as "proparts from sweden" ) also sell a replacement PCV hose Nr 5 with that same bad metallic valve integrated, this item should not be used !

if your mechanic told you they "serviced the PCV system", this should mean they also replaced that white valve, but it needs to be original; saab OEM (the hose with the OEM white valve is only 25 $ if i remember correctly, so it is not expensive). if they are not very familiar with saab they also might have not connected some PCV hoses correctly, but this is less likely

you can easily look at your own engine if this white valve looks newish (and its hose is not detached for ex), and to make sure they have not installed one of those proparts type metalic after market valves.





an illustration below of what the correct PCV hose with OEM PCV valve looks like

and an example of the bad PCV hose from Proparts (PPS) with the bad metalic valve they now use

[Anderson]

Assuming your recent oil consumption issue is related to a newly defective PCV system .(and not some of the other more serious causes mentioned earlier)....

below is a diagram of the components of the PCV system on your 2008 car model

The most important PCV valve (often referred to as the "white PCV valve") is a small one-way valve that is an integrated part of PCV hose Nr 5 (that valve is marked RED in color on this illustration). on older saab models you could just buy the white valve separately and replace it, on 2004-2009 models this white valve is integrated on PCV hose 5 and is now one replacement part Nr item.

PCV Hose 5 goes from the "oil trap" box (marked Nr 4 ) that is located at the back of the engine near the firewall, and comes up to the valve cover area , and the small white valve at the end of hose/tube 5 then has another short PCV hose (Nr 6 on the diagram ) attached to it that then goes to the throttle body (marked TB )

this white PCV valve is known to go faulty and is best preventatively replaced at major service intervals (but most mechanics or service centers dont do this )

the purpose of this white valve is to allow your throttle body to evacuate and slightly aspirate crankcase gasses from the engine when it is at idle and your car is stationary, preventing crankcase pressure from building up pressure. the valve opens with minimal pressure of air flow towards the throttle body, and completely closes when air/gas pressure tries to flow in the opposite direction ( when your engine is increasing revs and accelerating for ex)

you can get increased oil consumption if:
1) the white valve is defective and then causes increased crankcase pressure
2) if a new PCV white replacement valve is incorrectly placed the wrong way around (it is unidirectional, and should only allow air/gasses to flow TOWARDS the throttle body !). if hose 5 (on diagram) was replaced with an OEM saab part, it is now not possible to install the valve incorrectly (because it is integrated into the hose 5 ). but if just the valve was replaced by an amateur, it is possible they placed it the wrong way around !
3) if an incorrect replacement white valve was used with the WRONG specifications. many online retailers now sell a metallic fuel system valve (cheaply) that some people are installing to replace this white PCV valve, but this metallic fuel valve opens at the WRONG pressure and blocks airflow towards the throttle body
note: PROPARTS, a non-oem cheap aftermarkets manufacturer of saab replacement parts also sell a replacement PCV hose Nr 5 with that same bad metallic valve integrated, this item should not be used !

if your mechanic told you they "serviced the PCV system", this should mean they also replaced that white valve, but it needs to be original; saab OEM (the hose with the OEM white valve is only 25 $ if i remember correctly, so it is not expensive). if they are not very familiar with saab they also might have not connected some PCV hoses correctly, but this is less likely

you can easily look at your own engine if this white valve looks newish (and its hose is not detached for ex), and to make sure they have not installed one of those proparts type metalic after market valves.

Thank you very much. I will visit the local Saab repair technician on Tuesday and propose the solution you provided to him!

[silver2u]

Anderson,

you should maybe do a simple test yourself before you speak to your mechanic, it is referred to as "the PCV glove test" in saab forums.

when your car engine is up to normal operating temperature,
- let the engine idle normally, open the hood
- remove the engine oil filler dipstick
- attach a vinyl glove over the oil filler tube (and hold it securely in place )

then observe:
- if the glove wants to deflate and there is a vacuum in the pcv system and results in some light aspiration of air effect into the oil filler tube , this is a good sign that your PCV valve system is still functioning normally
- if the glove inflates like a balloon , this indicates there is increased pressure in your crankcase (bottom of engine part ), this is a bad sign and will usually indicate your PCV system is defective (or some other more serious mechanical problems can also cause this, but PCV should be fixed first (fixing the PCV system is NOT expensive )

this is the same type of test on a Volvo, showing bad pcv = inflation
https://www.youtube.com/watch?v=TzfHIFEF8ow

this is a healty pcv confirmation on another volvo
https://www.youtube.com/watch?v=-nfLL5GpgxQ

note: i would suggest you however have the warm engine running, then remove dipstick at oil filler location, and then fit glove while you hold it securely instead of just attaching it and then starting engine.
note 2: you have not mentioned leaking oil signs when you park your car , or smoke coming from exhaust etc .... so doing PCV function checks is the most logical first step
note 3: if you recently had a non-saab mechanic "do work on your PCV system" it is also possible some of the PCV hoses were not connected correctly or securely (for ex the PCV connection onto the throttle body might have become detached because there was no small clamp on it )