glenncof

Vehicle: 1985 Porsche 911 – at 171K miles w/engine never opened

Background:

Oil change interval (OCI) was 7500 miles under 100K (oil consumption at 17K miles was ~1500 miles per qt. when I got it)

Consistently used Castrol 20W50 since 100K miles, change interval of 3000 or less

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 (20+) times including checking every 100 miles after standard drive.

I’m a passive driver, no racing etc.

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 ?

Porsche says 600 miles per quart is typical. This is the company that recommended 15,000 mile change interval for this car !

bgiere

Oil shearing to a lower viscosity? Fuel dilution? I would run a less "evaporative" oil like Chevron Delo or Rotella T 15w40. BTW, oil change intervals for street driven 911's can easily be 15,000 miles with a high quality synthetic oil....many tests have verified it and some go even further.

theiceman

Is that the same as asking why you get worse gas mileage out of the second half of the tank than the first according to oyur gage?

911S3.6

15,000 mile oil changes, lifetime fill axles and transmissions are just another sales/marketing gimmick to sell more cars more often. By the way, the synthetic oil may questionably be good for 15,000 miles, but the crap that is caught up in your oil filter(s) is another topic altogether. This would be especially true of an air cooled engine that relies on it's oil and filtration even more. Just 'cause you don't get dirty at work each day doesn't mean you don't have to change your underwear!
Nick

pgrunwald

What's the analogy if you don't wear any - i.e. Air Cooled?

P.
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'87 Targa

fixnprsh

I don't buy into that 15K between oil change crap either. oil collects by products of combustion, one of which is acids, every BMW and Porsche I see with that many miles between oil changes, leak and burn oil. (Its not uncommon for BMW's that are slcaked in servicing, for the oil filter to come out in pieces) I would go no more than 5K on synthetic, and 3500 on conventional oil.

As far as a motor (a 3.2 no less) to burn a quart every 800 miles, eh, feed its habbit, it probably needs valve guides.

Food for thought, We won't look at oil consumption claims on BMW's with less than 6K miles on them, then its a quart every 750 miles is "acceptable" for our regular I-6 and V8's

Motorsport engines.................. sitting down? 2.5 quarts per 1000 miles!

Dan Cobb

I'm rather certain that your car is not intelligent enough to distinguish between an 'initial leak rate' and an 'after the first quart has leaked out on the driveway' leak rate.
My guess therefore has to be that the oil has broken down some after the initial 1200 miles.
(Unless you park it upside down after the first quart leaks out).

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