Reasons for engine oil level going down

[Gaurav]

Wondering to know what all reasons exists for engine oil level to go down by 10-15% in 4 months?

Last time for first time I changed engine oil to Shell 10W40 (semi synthetic) rather than Mobil 1 10W40 and continuously noticing that engine oil level dipstick was showing consistent drop week by week. It's approximately 3000 kms run out of its claimed life of 7000, whereas I change at 5000 due to extreme off-road use.

• There was no known leak spotted anywhere in and around engine bay.
• No oil spotting found on parking (solid concrete and tarmac)
• No coolant turned milky with presence of engine oil
• Engine color still shows half life (goldenish - brown)

Any help or suggestions are highly appreciated, thanks in advance.

[treks]

The only way that oil can disappear is because it is burnt in the engine if it is not leaking out Remember, all engines are designed to consume some oil, with the amount being burnt depending on the overall condition of the engine, but also on the type and formulation of the oil.

Some brands and formulations work better on some engines than others, but the reasons for this is very technical and depends on many factors- from the fuel used to the condition of the spark plugs to the average ambient temperature and even the average humidity. 

However, changing to synthetic or even semi-synthetic in older engines can do what you describe, since all the molecules in these oils are all of the same size, unlike in regular oil where the biggest molecules can be ten times (or more) bigger than the smallest. In practice, this means that more oil can escape past rings that are no longer perfect, so changing to synthetic oil on an older engine might not always be a good idea. 

Also bear in mind that you will not always notice if the piston rings are marginally worn. The engine may still perform perfectly and there may not always be visible smoke from the exhaust, but again, if the oil is "thinner" than what the engine is used to, you will notice an increase in the rate at which the oil level drops. Hope this helps.

[Barry]

Wasn't your rear crankshaft oil seal leaking? Leaky seal won't drop oil out when it's parked but can drop it on the road when you're driving and you won't see. Take a look around the bell housing and it will give an indication of how bad the leak is.

I agree with what treks said, it could be burning in the engine.  If the level is going down so quickly it's probably the cause.

If you're 100% sure the fuel system is in good working order, you can do an exhaust gas analysis and compare CO and hydrocarbons to that of a known good engine or a spec sheet. If they're abnormally high, it can indicate the oil being burnt in the combustion chamber. 

[Gaurav]

Thanks Treks for detailed explanation. I'm using 10w40 as it is recommended in owners manual and im using same since 7 years.

This is the first time I used Shell or else I stick to Mobil 1, if not very occasionally castrol edge or magnum something. May be this blend is not suiting or due to excessive heat this blend is getting burnt.....! Will see what happen after next oil change.

Thanks Barry, ill have a look at that crankshaft oil seal. Last it was still stuck at mild fever leak and not fully soiled about 3 months back.

 

[Ren13]

Hi gaurav if you feel it's happened the 1st time in 7 years due to change of brand of oil you using doesnt sound right but may be the quantity of oil put by the technician could be less by mistake especially if the oil used is different he must have not got a judgement. You can always topup the oil level and recheck after 2000km where it's due for oil change any ways and you will get an idea and your doubt clear.

Edited August 3, 2017 by Ren13

[Gaurav]

@Ren13 people who know me well, they also know how big car fanatic and attention detail seeker I am. After spending half of my life in Dubai, I always double check everything when it comes to my cars, no matter whoever (technician / mechanic) touches my car. I check oil level every week in all my cars and same I have done in this scenario too, oil level was much between two lines just a tad shy than upper mark (great).

Yesterday it was little below the lower mark. And gap between two lines is over an inch to let you understand the engine oil maths going around. I topped up with Mobil1 around 800ml and now waiting to observe further now.

I have only topped up engine oil in my Cayenne turbo every 1500 kms, as advised in manual and as alerted by car in dash reminder "Low oil" other than that I never topped up engine oil until the next service - be it 5k, or 10k. This was indeed weird and that's what making me little paranoid that how why engine can reduce 800 ml in about 3000 kms in 3 months......?

[Barry]

0.8 liters in 3,000 kms might seem like a lot but in reality, it's not actually that bad. I understand it's bad if the engine didn't do it before the oil change though. 

I used to date a girl who drove a 7th generation Toyota Celica and it used a liter every 1,000 km. She complained to Toyota and they told her that was normal consumption for the engine. Sorry, unrelated, just a story. 

[treks]

I suggest you try and find a shop that can do an exhaust gas analysis, but they must check at least five gasses, with the most important being sulfur. The reason for this is that semi-synthetic oil contains some sulfur in  the mineral base oil component of the blend, so if a properly calibrated gas analyzer finds high levels of sulfur in the exhaust gas, you will know that you are burning oil. 

Edited August 4, 2017 by treks
typo

[Ren13]

11 hours ago, Gaurav said:

@Ren13 people who know me well, they also know how big car fanatic and attention detail seeker I am. After spending half of my life in Dubai, I always double check everything when it comes to my cars, no matter whoever (technician / mechanic) touches my car. I check oil level every week in all my cars and same I have done in this scenario too, oil level was much between two lines just a tad shy than upper mark (great).

Yesterday it was little below the lower mark. And gap between two lines is over an inch to let you understand the engine oil maths going around. I topped up with Mobil1 around 800ml and now waiting to observe further now.

I have only topped up engine oil in my Cayenne turbo every 1500 kms, as advised in manual and as alerted by car in dash reminder "Low oil" other than that I never topped up engine oil until the next service - be it 5k, or 10k. This was indeed weird and that's what making me little paranoid that how why engine can reduce 800 ml in about 3000 kms in 3 months......?

Apologies gaurav.

[Gaurav]

19 hours ago, Ren13 said:

Apologies gaurav.

No need to apologies Ren, as you were just helping me with best of your knowledge and experience. Later, I just explain my side to clarify and hope to get an appropriate help needed.