Vehicle: 1985 Porsche 911 – at 171K miles w/engine never opened
note: 12 qt oil capacity
Background:
OCI was 7500 miles under 100K.
Consistently used Castrol 20W50 since 100K miles, OCI of 3000 or less. Using Mahle OC-54 filter (factory).. This engine is known for strong lower end but soft valve guides (which leads to oil consumption).
Current oil consumption after oil change; 1 quart for initial 1200 miles, 1 quart for subsequent 800 miles, thereafter 800 or less miles per quart. I’ve done this check many times including checking every 100 miles after standard course.
Porsche says 600 miles per quart is typical. This is the company that recommended 15,000 OCI for this car !
My questions:
1) What is the likely cause of this increase in oil consumption from the initial 1200 miles to the subsequent 800 miles ?
2) It appears 7500 miles OCI did not completely prevent wear. How could a company like Porsche recommend 15,000 OCI ?
Comments ?
note: 12 qt oil capacity
Background:
OCI was 7500 miles under 100K.
Consistently used Castrol 20W50 since 100K miles, OCI of 3000 or less. Using Mahle OC-54 filter (factory).. This engine is known for strong lower end but soft valve guides (which leads to oil consumption).
Current oil consumption after oil change; 1 quart for initial 1200 miles, 1 quart for subsequent 800 miles, thereafter 800 or less miles per quart. I’ve done this check many times including checking every 100 miles after standard course.
Porsche says 600 miles per quart is typical. This is the company that recommended 15,000 OCI for this car !
My questions:
1) What is the likely cause of this increase in oil consumption from the initial 1200 miles to the subsequent 800 miles ?
2) It appears 7500 miles OCI did not completely prevent wear. How could a company like Porsche recommend 15,000 OCI ?
Comments ?