Q: Should one read the oil level with the dip stick screwed in or just resting on the threads?
Gary Brown, via email
A: Gary, I’m glad you asked this question even though I can see the boys in the hangar beginning to smile about it. First of all, it’s not quite as simple as it sounds.
If you stop and think about it, how many different engine models and airframe installations do you think there are out there? The combinations would probably blow your mind, and then the next question that comes to mind is how many different dipsticks would be needed.
The choice of dipsticks actually begins when the aircraft/engine design work begins. The airframe manufacturer takes the lead in determining which dipstick will be used because he knows how the specific engine will be mounted and the number of degrees tilt, etc., the engine will have or whether the engine will be utilized on a twin-engine aircraft.
Each dipstick must be calibrated taking all of these factors into consideration. It is certainly not a case of one size fits all.
So, for those of us that believe close is good enough, it’s probably okay to check the oil with the dipstick just resting on the threads. But for those of us who suffer from OCD/ADD, we will certainly want it screwed down tight when checking our oil.
We also shouldn’t forget that not all dipsticks screw in because some use a cam-action type method to secure them in place. It’s this type that most folks would properly secure when checking the oil.
This all may sound like a bunch of gibberish, but it’s an important part of using common sense and setting standards for yourself by doing it the same way each time the oil is checked.
It doesn’t makes that much difference which way you do it, but rather that you do it the same way each time.
We find that on many engines a full indication on the oil dipstick constitutes a waste of money. The engine will just toss it out the breather line. But, there is a “sweet spot” for adding oil and once that is determined you do not waste so much oil.
On my engine the dip stick is reading full at 8 quarts. It will run just fine at 5 and 1/4 quarts and burn very little oil…but we check all the time….and watch temperature and pressure.
One thing I do know is that when operating over aeroplane unfriendly terrain, I want the dip stick reading full !
With homebuilt aircraft, dipstick reliability is questionable because the tilt of the engine etc. might change due to a different mount etc.
Err on the side of caution!
The TYPE CERTIFICATE for your aircraft will tell you how much oil the engine should have. You can add that amount of oil, when changing it, check your dipstick, and determine the accuracy of how you check your oil. You may be surprised; I have found several that were inaccurate, up to 2 quarts.
I chuckled when reading this, because as a former owner of a 1947 Beech Bonanza, checking the oil is a procedure that is different from most.
The early model Bonanzas were fitted with Continental E series engines.
This means that the engine did not “store” the oil in a normal fashion. The engine used an external oil tank with a cam type dipstick. The result of this is that when checking the dipstick with a cold engine, it would read close to 0. After running the engine for a short period of time, the oil in the tank would begin to rise. After a flight, the oil would very gradually leave the tank to go back into the engine. The result of this was that the best time to check the dipstick was after the engine had been run, the oil was hot and the engine oil pressure had returned the oil to the tank.
Supposedly there was a check valve in the tank to prevent this “drainage” from happening, but they never worked. Every owner I know with this arrangement experienced the same phenomenon. The many mechanics I used through the years all said the same thing—it’s normal, keep your eyes glued to the oil pressure gauge when starting up and for a visual, check the dipstick immediately AFTER you have run the engine. They also said that in their experience, replacing the oil tank check valves would not solve the problem in the long run.
I wasn’t crazy about this but got used to it. I always new how much oil was in the engine, checked the oil level after a flight, and as the mechanics suggested, keeping my eyes glued to the oil pressure gauge after start up.
Although I and others never had a problem, I’m glad that newer Continental & Lycoming engines do not use the oil tank which means an accurate read on the dipstick—hot or cold. It helps the peace of mind.
Hmm – there’s got to be more to this than meets the eye. Never really thought of all the varied types of (oil?) aviation engine dipsticks out there. I just unscrew it, pull it out completely (with rag in hand, to avoid dripping on the apron or hangar floor) and if it reads 8 1/2 I’m good to go. Anything less than that I add a quart. I usually remove, read, wipe and insert and repeat the entire steps a second time just to make sure my readings are correct.