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Oil Level After Flight

n74846

Well Known Member
I have been concerned about oil consumption either through burn or vent. To double check the level today I did an after flight burp and measure. I was surprised that the level was higher than a cold burp level. Which is the correct level to monitor? ( I am in So Fl for temp reference).
 
I understand the most accurate oil level is taken after burping a warm engine. More of the residual oil in the case is pushed into the tank. When cold, some of the oil doesn't get squeezed out of the engine. A good practice is to always burp after your last flight of the day and confirm the level. If you don't see oil under the plane the next day, you are good to go.
 
Forgive my ignorance, but what is "burping"?

This is the RV-12 forum and burping is what we lovingly do to our Rotax engines before we put them to bed. It is slowly turning the prop so that the compression leaks will pressurize the crankcase and push any pooled oil in the bottom of the case and oil lines back into the oil storage canister on the firewall.
 
I have never burped my engine warm. I usually run about 3/4 high in the dipstick range cold. It seems to me that looking at the warm level is not of much value as long as I have my good cold reading. If Mr. ROTAX thinks it's too high it will just blow it out the tank vent.
 
Using the same burping procedure, I always find my oil level higher after a flight when hot. About halfway from add mark to full mark difference.
 
Me too....always higher up the dipstick when burped hot. I usually don't burp it cold anymore - always do it hot after landing, much quicker - but did so today because I hadn't flown for a couple weeks. Oil was just above the bottom mark cold but above half when hot after the flight.

Jack
 
Coefficient of thermal expansion?

I always find my oil level higher after a flight when hot.
I don't know the geometry of your oil tank or how many quarts are in your engine, but the coefficient of thermal expansion of motor oil is .00039 per deg. F. That would work out to roughly a 3% increase in volume for an 80 deg. F temperature rise. I guess you could work out how that might show up on your dipstick. If your Rotax holds 7 qts. at room temp, the volume would be 7.22 qts. at 150 F.
 
I don't know the geometry of your oil tank or how many quarts are in your engine, but the coefficient of thermal expansion of motor oil is .00039 per deg. F. That would work out to roughly a 3% increase in volume for an 80 deg. F temperature rise. I guess you could work out how that might show up on your dipstick. If your Rotax holds 7 qts. at room temp, the volume would be 7.22 qts. at 150 F.

"I'm not an engineer" but its not about the expansion of warm vs. cold oil. Rotax only holds about 3 1/2 total quarts to begin with. More likely, that less sticky, cold oil remains in the crankcase when the engine is burped when it is warm. Whatever approach people use, being consistent when the burping/measure is taken, is probably the best practice.
 
Thanks for all of the input. I will henceforth, visualize oil level prior to flight, but burp measure post flight. That may be the reason I though I was losing oil in the first place.
 
You might want to consider burping prior to first flight of the day. One of the reasons for burping is to insure that oil from the storage tank doesn't migrate back into the engine when the airplane sits for extended period. Oil tank is higher elevation than engine crankcase. Burping ensures that there is no excess oil in the crankcase which could cause a cylinder hydraulic lock and expensive repair. I don't think this has every happened on the RV-12 Rotax 912 engine installation but insurance and peace-of-mind is cheap.
 
Burping "warm" is a bit misleading. That oil tank and cap are pretty darn HOT right after a flight. Better use gloves if you are checking oil level immediately after flight. To me it's more important to know how much oil I have BEFORE starting than AFTER flying. I'll stick to checking the level cold. Remember ROTAX says check it cold against the dipstick marks. When you start using a cold landmark to judge hot conditions you are outside the OEM intentions.
 
Now that everyone is confused here is another thought.:p It takes many more spins of the prop to burp when cold, where as when checking after flight it only takes a few spins to burp. Now if you have your own hanger a simple visual check by the nose wheel will tell you right away if you leaked any oil before flight after checking the last time after flight.:) In cold weather it doesn't hurt anything if you engage the starter for about 5 seconds before hitting the ignition switches one at a time to move a little oil around the engine if you haven't flown in a while.:D
 
In cold weather it doesn't hurt anything if you engage the starter for about 5 seconds before hitting the ignition switches one at a time to move a little oil around the engine if you haven't flown in a while.:D

Well, yes it could hurt something... See my post above about hydraulic lock. Same reason lower spark plugs are pulled on a radial engine before initial start of the day. Hydraulic lock can very easily bend a connecting rod.
 
I think it's good practice on the rotax to burp the engine before each flight, just a few revolutions ensures oil to the tappets and that's going to prevent some initial startup engine wear.
 
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