View Full Version : CFI Pop Quiz #120 - Oil Temp
01-20-2006, 05:32 AM
An abnormally high engine oil temperature indication may be caused by
A) operating with a too high viscosity oil.
B) operating with an excessively rich mixture.
C) the oil level being too low.
01-20-2006, 08:04 AM
im going with C
01-20-2006, 08:23 AM
C for me too
01-20-2006, 08:29 AM
I'd have to say both 'C' and 'A'. C seems obvious, since there is less material (oil) to absorb and transfer the nominal heat. A can be an issue though, if the machine is reliant on an oil radiator, since less volume will be passed through the system in a given period of time.
So how did I do? :)
01-20-2006, 08:33 AM
Viscocity too high can be pretty interesting from an oil pressure standpoint especially when cold - used to work for a guy that believed in straight weight Aeroshell 120 (60 weight) for his Bell 47's all year round, you can't imagine what those engines sounded like when first started at 20-30 degrees F! None of his engines would ever make TBO - switched to a good quality multiweight, problem solved. Engines started making TBO, imagine that :)
01-20-2006, 09:25 AM
Correct answer is "C". Oil viscosity and rich mixture are normally considered to help cool the engine. Oil helps dissipate heat, so low oil is the answer. I'm sure we could make issues here (legendre) but that is not my goal. The goal is to help understand where the FAA is coming from on these test.
01-20-2006, 10:25 AM
C - Many an aircraft/engine has unnecessarily been destroyed over oil loss.
A - Has some truth to it, but nothing like c.
01-20-2006, 11:45 AM
I have no interest in making an issue of anything (at least not until I'm smart enough to get myself in trouble.. hehe). Whenever I see multiple-choice questions, I don't rule out more than one 'correct' answer.. unless I'm told that there is only one choice per answer.
Didn't realize that you were pulling these direct from an FAA test. Nice idea, I'll keep my eye on these threads.
01-20-2006, 12:29 PM
Now here a question if your oil is at180 degrees what should be your engine CHT.
This apply to air cooling engine
01-20-2006, 03:57 PM
IME, 180F is totally normal for an air-cooled engine that is producing better than half its rated power; maybe even a little on the cool side. It's not unusual to see oil temps in the 220F range, even on water cooled high-perf (car) engines. 180F certainly shouldn't be dangerous.
So, assuming that the engine is at a nominal operating temperature (based on 180F oil), the CHT should be around the 350F mark.. plus or minus 25F or so, and obviously relative to air temp.
Thing is, if something truly wicked is on the way, the CHT will give you indication much faster than the oil temp will. By the time oil temp is into the red, it might be too late for the pistons and cylinders.
Anyway, that is all based on my exp with motorcycles and so forth. One of the reasons I'm here is so you all can help me re-learn / un-learn what I need to, so I can safely operate aircraft engines. Correct away!
01-21-2006, 02:56 AM
There is a rule of thumb that said that your CHT should be around twice your oil temp. This help to check if the engine is working ok, your senders are ok.
If the delta is more than 50 degrees if a flag to check the engine.
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