new to me 914 needs an oil change. car has "tuna" can sump, remote oil filter and cooler. cooler is located in back, mounted high under under trunk.
estimate of how much oil it holds?
does the oil cooler drain back to the engine?
with engine warm, where should oil be on dip stick?
thanks Dave

Measure how much you've drained out and replace it. Can't really know how much oil in the oil cooler will actually drain out or be trapped. The tuna can sump extension doesn't really add too much capacity, but you have to be extremely careful to not over torque the bolt holding it on!

Try to fill about half way between the marks on the dipstick.

I have the exact same setup. I remove the oil lines at the cooler which drains the cooler and most of the lines. I also remove the tuna can. I put 4 qts and take her for a drive to make sure the cooler is filled (mine uses a thermostat sandwich adapter) and top off to the full line (top line on the dipstick). My last oil change required an additional 12oz of oil after the drive.

With the cooler mounted high, does the oil drain back when the engine is shut off? Does that change the dip stick reading? Upon startup, does it need to pressurize the system?

Oil drain back is not noticeable when checking the oil. I've been doing the method I've described for 7 years with no issues...that's all I know. Others may have more info