There does seem some reluctance to accept the idea that an engine can be low on oil yet not experience a temperature increase. An engine with a 40 gallon oil tank, for example, may well be at 20 gallons and show no increase. The oil cooler continues admitting or bypassing oil as needed, and unless some change occurs with in the engine to cause abnormal temperatures (bearing failing, for example, or a bearing oil jet plugged), the temperature may not provide much clue.
Likewise, as the quantity falls, so long as the pump doesn't cavitate, it's output will typically remain constant, and you will very likely see no pressure change. As temperature gets higher in some engines (and it may get higher due to less oil, or it may not) depending on the system, pressure may decrease...or it may remain constant. The type of oil system and pump makes a difference.
In some systems, excess oil, especially early in the operation of the engine before systems are warm, can cause oil bypasses to open and you'll actually see a drop in pressure, rather than an increase...the same may be true of oil quantities in a given system; less oil doesn't necessarily mean less, or more pressure.
We've seen from the example provided by airflorida1 that many causes can be responsible for a given engine indication. As a mechanic, we generally start with the most simple and easiest/least expensive, and go from there...checking quantity is simple, easy, and inexpensive. However, one should not make the mistake of assuming that once a low oil quantity is found, the problem is solved. What caused the oil quantity to be low?
Some engines inherently burn large quantities of oil. In our R2600's, for example, I routinely put in 20 gallons of oil each time I added fuel. In a TPE-331 turbopropeller engine however, oil is added by the pint and the engine shouldn't be using oil. The competition, the PT6A, does use oil, and it's to be expected...but in either case a loss of oil may or may not show up as high temperature or low pressure. Such an analysis is far too simplistic, and not enough information is provided.
We can expound on this all day, but at the risk of being accused of providing "rhetoric."
Last edited by SNS3Guppy; 23rd Jul 2009 at 09:13.