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Old 04-14-2017, 03:01 PM   #1
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Heavy oil consumption

I've had oil consumption ever since I bought the car 4 years ago at 45k miles. It was mostly a quart per 5k miles for 3.5 years until my AOS blew last fall. I replaced the AOS but my oil consumption vastly increased. I replaced the AOS again (assuming the new one was faulty) along with the PCV but the consumption remained high. No drips underneath. No unusual visible tailpipe smoke. Water fluid is clean. I did compression/leak down tests and the numbers were good.

I've now burned 7 quarts in the last oil change cycle of 5k miles with the car at 92k miles. Where else could my oil be going?

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Old 04-14-2017, 04:16 PM   #2
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just to clarify...

...seven quarts in 5,000 miles?
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Old 04-14-2017, 04:51 PM   #3
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There is a special way of testing for ovalized bores. Others may be able to explain that.
Does the rate of consumption vary depending if the sump level is max or min on the dipstick ?
Measure HC in the Exhaust?
Plug condition may give a clue?
Is drained oil filthy black (carbon)?

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Old 04-14-2017, 09:33 PM   #4
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Yes 7 quarts. Consumption rate doesn't vary for the sump level. Oil is clean and more clean that it usually is after 5k miles due to the replacement oil.

I'll pull a plug tomorrow. I did read about the bores but if it was ovalized wouldn't that effect the compression/leakdown?

Thanks!
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Old 04-14-2017, 09:37 PM   #5
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7 quarts per 5000 miles is 714 miles per quart.

Porsche spec's excessive oil consumption at 600 miles per quart so while your experience is certainly on the higher side, Porsche would say that its within the range of expected oil consumption.

In regards to where the oil is going, there are only a couple of places it can go: external, coolant, or combustion chamber.

If there are no external leaks and the coolant looks clean, then its most likely going into the combustion chamber. Pull a couple of spark plugs to confirm. If this is the case, they will be coated in oil (whereas they should normally be a dry tan color).
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Old 04-14-2017, 10:41 PM   #6
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Cylinders #5 & 6 seem to be the weaker bores according to Hartech in the UK - that's the 2 rearmost cylinders on the drivers side (LH drive cars). Valve stem seal/guide wear can also cause oil burning but I haven't heard of that in the M96 engines.
As Tom says, pull those 2 x plugs and compare with (say) #4 cylinder for comparison as they are all on the same side, though comparing all six plugs should give a better indication ....
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Old 04-15-2017, 05:56 AM   #7
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This had me wondering, do you guys trust the electronic oil level sensor or always use the dip stick. I haven't used the stick in a while. Getting lazier as I get older.
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Old 04-15-2017, 06:50 AM   #8
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I think Porsche calls 1.6 qt per 1000k an acceptable consumption. That seems a bit high.
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Old 04-15-2017, 07:32 AM   #9
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Man that is a lot of oil. You'll have to start measuring your fuel economy in Miles Per Quart. Seriously though, if you are actually burning that much oil I can't imagine there not being a constant blue tinged exhaust and the exhaust tips showing evidence of oily residue.
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Old 04-15-2017, 09:31 AM   #10
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5 &6 are 'at the end of the line' for coolant and oil circulation so are more prone to ovalisation but with this amount of consumption you have to think it would be more than just 2 cylinders?
As I speculated earlier- plugs will tell the story
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Old 05-28-2017, 09:32 PM   #11
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Finally got able to pull a plug. #6. This looks more like ash deposits from fuel. 13k miles on the spark plugs.



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Old 05-29-2017, 09:18 AM   #12
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