Burning less Oil After Road Trip???

[isby]

I’m on the way back from a 1600 mile road trip in my 84 3.2L. It has always burned a fair amount of oil, maybe 1 quart every 500-600 miles. This held true on the first leg of the trip. However, on the way back, it is burning noticeably less oil. My guess is that it hadn’t been on a long trip like this in 20+ years. Any theories on why oil consumption has improved?

[icarp]

The oil system in the 911 likes to have the tank filled to the lower fill mark when HOT
If you fill it all the way to full on the dipstick it creates more crankcase pressure and consumes oil at a higher rate.

Simple

ian

[isby]

Interesting. Thx!!

[MrBonus]

Originally Posted by icarp

The oil system in the 911 likes to have the tank filled to the lower fill mark when HOT
If you fill it all the way to full on the dipstick it creates more crankcase pressure and consumes oil at a higher rate.

Simple

ian

Thank you for this explanation. I noticed in my '89 and now the '71 a similar phenomena. If I leave the oil fill somewhere in the middle or slightly below on the dipstick, it consumes no noticeable oil but if I fill it up to the top, it will burn off a half quart relatively quickly, then consume no meaningful oil after that between changes.

[Bill Douglas]

Or the long road trip burnt off carbon around the piston/rings/cylinder and everything fits better and tighter.

[jac1976]

Or it’s out of oil.

[tk32]

^ Im glad I clicked on this thread, thanks for the afternoon chuckle

[pmax]

Originally Posted by jac1976

Or it’s out of oil.

Yep, 1600 miles is 3+ Q, there was a presumption made that it was run "low" which is unlikely.

OP can confirm.

Originally Posted by Bill Douglas

Or the long road trip burnt off carbon around the piston/rings/cylinder and everything fits better and tighter.

These cars don't run well after sitting for a while, that's for sure.

[ahh911]

No difference in oil consumption between minimum and 3/4 level for me.
Consumption increases dramatically in either scenario when continually pushing above 5k rpm on twisty roads for prolonged periods.
I think it's a bad idea to run these low just so that you don't have to add 1/2 a quart every 2 or 3 weeks. I was in that camp thinking it might help (it didn't) and now realize it was an error and won't return to that mode of operation, it borderlines on reckless. I keep it over 1/2 full nowadays.

Phil

[rwest]

I have also noticed that on long trips my consumption is down as well. My best guess is that the motor is running at maximum expansion for long periods of time and therefore not as big of gaps for oil to leak through and burn.

Because air cooled engines need larger tolerances, that when you do shorter trips, the engine spends more time in “sloppy” clearances and more oil gets past.

Just my thought without any scientific evidence to back it up!

[rokemester]

This is something we always talk about! These cars are happiest when they are DRIVEN! Fun thread.

[isby]

Originally Posted by jac1976

Or it’s out of oil.

This actually made me laugh out loud. But just to set the record straight, it was not out of oil.

[pmax]

Originally Posted by isby

This actually made me laugh out loud. But just to set the record straight, it was not out of oil.

How many times did you top it up and to what level each time ?

[wazzz]

Originally Posted by rwest

Because air cooled engines need larger tolerances, that when you do shorter trips, the engine spends more time in “sloppy” clearances and more oil gets past.

Just my thought without any scientific evidence to back it up!

This is exactly what I thought too.

These cars do need to be driven. Mine sat for over 6 months last winter without a turn of the key. When I took it out for its first run in April, I noticed an extended oil puddle like I had never seen before. Something like 1/4 liter maybe. Now that I drive it quite regularly, no more puddle. I know I have a leak somewhere and will need to address it some day, but that's only a few drops in a while and nothing like this big puddle she squirted last winter. Weird.

[spuggy]

Originally Posted by MrBonus

If I leave the oil fill somewhere in the middle or slightly below on the dipstick, it consumes no noticeable oil but if I fill it up to the top, it will burn off a half quart relatively quickly, then consume no meaningful oil after that between changes.

Yeh, my 930 has done exactly what icarp and you describe for years - I long ago gave up on trying to keep the oil level above half way on the stick. You'd just be constantly adding more oil - only for the motor to blow it out the breather at higher RPMs.

Also, motor uses more oil when cold/clearances are bigger. So relatively short journeys where it's cold for a larger %-age of the time will use far more oil than getting it up to operating temperature and staying there for hours - where, comparatively, it uses almost no oil IME. So long as there's no leaks, of course - otherwise it's just a constant loss system....

The only downsides of running 10-20% less oil in a dry sump system is that the oil that's left gets to work a little harder, and the heat being carried away is being absorbed by less oil - so will probably run a tad hotter. There are ways to increase the capacity of the oil system, however.

[E Sully]

Here's a quote of mine from an old thread on the subject.

Originally Posted by E Sully

I remember years back, it seems that oil level senders and dipsticks were updated.
"Porsche Oil Level Sending Unit For Models Thru 1980 Use Updated Dip Stick Part # 93010773101 With Gasket" " Dipstick, Oil Updated, For Models Thru 1980" description was included back then.
From what I gathered, it seemed that the updated units were due to Porsche lowering the recommended oil level in the tanks. With the new units calibrated for this lower level, the oil level gauge and dipstick would show full with a lower amount.
While I used to see this description back in the day on Pelican, they no longer state this. Another vendor that I will not name, since they are a competitor to Pelican, still does.

This customer review from Pelican for their oil level sensor seems to reflect the new level.
Andrew W. July 18th, 2016
"1979 930
OK part. Was not exactly like the original. Float arm was shorter so it did not read the same as the original part. Replacement parts should match the specs of the original parts."
Here's a thread on the topic.
Which length oil dipstick for '74 - '89 oil tank?

[proporsche]

you do not need to shorten the oil level sending unit.All you have to do is synchronize it with the inside gauge by bending these stops on it..one is for top and the other for bottom level

Ivan

[darrin]

isby -- wondering whether the root cause of your oil consumption is worn valve guides. do any of your spark plugs look/get oil-fouled? How many miles on your '84? Have you checked your valve stems for lateral motion?

[GH85Carrera]

I just returned from 3,000 miles of driving. Some on tracks like Talladega at 125 MPH. Barber Motorsports, during a DE. I kept the oil level at the lower mark on the dipstick with the oil temp at 210. I only used one quart over the trip. I turned 195,000 miles on track at Barber Motorsports.

[icarp]

Originally Posted by darrin

isby -- wondering whether the root cause of your oil consumption is worn valve guides. do any of your spark plugs look/get oil-fouled? How many miles on your '84? Have you checked your valve stems for lateral motion?

A perfect and fresh engine will consume oil if the level is kept to the full mark on the dipstick , assuming the oil is up to temp.

I do not think there is anything wrong with the OP's engine .

The 911 engine needs more than 20 minutes to get all the oil up to proper temp.

Ian