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  #11  
Old 09-28-2021, 09:03 PM
RFSchaller RFSchaller is offline
 
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Location: Phoenix, AZ
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120F seems to be a common number for a lot of rotating equipment oil.An explanation I have heard is viscosity at lower temperatures causes reduced flow through the orifices that feed the bearings.
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  #12  
Old 09-28-2021, 09:39 PM
jnmeade jnmeade is offline
 
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Location: Iowa
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My observation is that if oil temp is 100°F, oil pressure is down in the 60 lb range so oil viscosity is in the working range or close to it. Oil RPM above 2500 RPM is in the yellow or caution range up to about 4000 RPM. If Rotax didn't want me to operate the engine above 2500 until oil temp was 120°F they'd have put a red line in the RPM gauge, not yellow, is how I operate it.
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  #13  
Old 09-28-2021, 10:23 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post

EDIT
The second part of the reason for the limit (that I forgot when I initial wrote the post) is that because the crank case pressure is used exclusively to push oil back to the tank, if the rpm gets too high before the viscosity is low enough, the pump can suck oil from the tank faster than crank case pressure can return it to the tank. If this goes on for too long, the oil pick-up can suck air which would result in oil pressure loss.
I edited my initial post with additional info above that I had forgotten to add initially. This is the most important reason for the limitation.
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  #14  
Old 09-28-2021, 11:41 PM
seagull seagull is offline
 
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The Shell Sport 40 oil is rated as a 10W-40 oil. This means it is 10 viscosity at “0” degrees Fahrenheit and 40 viscosity (thicker) at 212 Fahrenheit. The oil is changing viscosity, getting thicker, as the engine warms up. Doesn’t this resolve what is being discussed above?
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  #15  
Old 09-29-2021, 01:24 AM
NinerBikes NinerBikes is offline
 
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A 10 Winter motor oil at 0F has a flow rate of 150 to 160 centistokes, thick and slow.

A 40 weight motor oil at 190 to 220F has a flow rate of 13 to 14.8 centistokes. thin and fast




What is the centistoke range of that motor oil at 110F ? 70 ? 75? 80? centistokes?
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  #16  
Old 09-29-2021, 04:52 AM
bobnoffs bobnoffs is offline
 
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10w-40 means the oil has the viscosity that 10w wt. oil would have at 0 deg. not that its viscosity is 10w.
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  #17  
Old 09-29-2021, 05:12 AM
thiggins thiggins is offline
 
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Location: Saluda,NC
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Does Anyone know of a good Rotax person near Western NC/Asheville , NC?

Is getting a BUDS connector and software worth doing?
Would it show oil pressure in the logs ?
Where do we get a BUDS connector anyway?

Thanks for all the input/information, very helpful.
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  #18  
Old 09-29-2021, 07:28 AM
R100RS R100RS is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
EDIT
The second part of the reason for the limit (that I forgot when I initial wrote the post) is that because the crank case pressure is used exclusively to push oil back to the tank, if the rpm gets too high before the viscosity is low enough, the pump can suck oil from the tank faster than crank case pressure can return it to the tank. If this goes on for too long, the oil pick-up can suck air which would result in oil pressure loss.
Interesting explanation. Is it mentioned in ROTAX documentation?

Since blow-by around the rings is where the crankcase pressure comes from, crankcase pressure should increase with engine RPM, just as the output from the engine-driven oil pump increases. After all, even without combustion pressure driving the pistons (and creating blow-by) in a running engine, there is enough pressure in the crankcase to push all the oil out of the crankcase when burping a cold engine.

At 100 degrees F, it is hard to imagine such a phenomenon (oil accumulation in the crankcase) occurring at any RPM.
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  #19  
Old 09-29-2021, 07:56 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by R100RS View Post
After all, even without combustion pressure driving the pistons (and creating blow-by) in a running engine, there is enough pressure in the crankcase to push all the oil out of the crankcase when burping a cold engine.
Actually there’s not. At least not enough to push all of it back to the tank. A very common cause of people overfilling the oil tank is when checking the oil when it’s cold, particularly when it’s very cold, and then adding oil based on what the dipstick reading is. When the oil is cold it’s still leaves a very thick coating on the interior of the engine case even after an air bubble has been pushed up through the hose back to the oil tank, causing the classic burp.

No, this info is not in the documentation but it is taught by some instructors in the maintenance classes.
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RV-6A (aka "Junkyard Special ")

Last edited by rvbuilder2002 : 09-29-2021 at 08:03 AM.
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  #20  
Old 09-29-2021, 08:16 AM
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jrtens jrtens is offline
 
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Quote:
Originally Posted by thiggins View Post
Does Anyone know of a good Rotax person near Western NC/Asheville , NC?

Is getting a BUDS connector and software worth doing?
Would it show oil pressure in the logs ?
Where do we get a BUDS connector anyway?

Thanks for all the input/information, very helpful.
You will be able to get engine and flight data logs from your Dynon or Garmin system. (oil pressure and much more)

BUDS might be necessary to find problems with the ECU, ignition and fuel injection systems, but not always. And, it usually requires an experienced Rotax AMT to read the data.
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