How to properly check oil level on your 911
By D. N. McNALLY, ME
Northeast Region
Much of the grumbling concerning excessive oil consumption and excessive oil leakage on
the 911 is directly attributable to an extreme oil level. The 1966 911s and the 1967 911S have an oil level gauge on the dashboard. This will
give an accurate reading only if the engine temperature is at least 140F
and the engine has been idling for at least 20 or 30 seconds. It should never read more
than 7 quarts which is the corresponding high mark on the dip stick. Adding a quart should
never be done unless the gauge comes to rest in the red field below the 5 quart mark.
The same applies when checking the oil level with the dip-tick. Pull out the stick,
wipe it clean and insert it into the little tube inside the oil tank neck at the top. Make
sure you push it all the way home. It has only 2 marks—a high (7 quarts) and a low (5
quarts) mark. Add one quart only if the oil level is at the lower mark.
This seemingly illogical procedure is necessary because the 911 engine has a “dry
sump” lubrication system just like those used on many racing and most aircraft
engines. When the engine is at normal operating temperature the oil reserve is all pumped
out of the crankcase, through the filter, and into the oil tank. This situation prevents
the oil from surging and splashing around in the crankcase, thereby reducing windage
losses. Thus the engine can produce more power output and the oil has less heat to
disperse.
When the engine is not up to proper operating temperature the oil has a harder time
getting through the full-flow filter and it backs up in the crankcase. An oil level check
at this time is not valid since all of the oil is not yet in the tank.
For the same reason the engine speed must not be taken up over 4000 rpm because the oil
flow cannot be then keeping up with the needs of the lubrication system. It is, however,
permissible to “load” a cold engine since the full pressure lubrication system
provides adequate oil to all the critical points. So, after starting a cold engine merely
drive away slowly as soon as the engine is running smoothly.
So, the correct time to check your oil level especially on the 1967 911 is when you
reach a destination and the engine is warm. If you take care of the oil level at this time
the car will be ready for you the next time you want to move.
Because the filter in this full-flow system is critical to its proper performance it
should be changed at each oil change. This, normally, is every 6000 miles but it should be
done every spring and fall regardless of mileage. When the oil is changed no more than 8
quarts should be put in until the car has been driven at least 100 miles. Then check the
level as described above and add if needed. Because, if too much goes in it will back up
into the induction plenum and coat the air filter with a thin film. It will also blow out
of every nook, crack, and cranny it can find in the engine because it will back up in the
crankcase. The oil tank itself holds only 7 quarts, the rest must find space in the
induction plenum and the crankcase.
As for the minimum the engine may safely be operated up to 4000 rpm with as little as 4
quarts of oil in the tank. At the present time oil filter cartridges for the 911 and 911S
should be obtained through a Porsche dealer only since filter area and by-pass valve
pressure have to be matched. With this proper balance consumption should run 600-700 miles
per quart. If it is substantially less and you have followed these procedures, see your
dealer.
6/68
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