Question for engineers?!

[RatsoreA]

Ok, here is my question.

On your average run of the mill high power aero engine, where is the oil temperature measured from? Is it measuring sump oil temperature, or is it taken off an oil gallery in the same vein that a cars water temp is measured?

What difference would it make? What would be a better indication of engine health?

Ok, flame on!

[toolowtoofast]

If it's in the green range, it doesn't matter where it's measured from - the engine or airframe manufacturer has decided it is best where it is.

[RatsoreA]

Thank you for answering a question I didn't ask with an answer I already knew!!! :p

Seriously, anyone else?

[ampclamp]

Dont think I've seen one in a sump or tank.Run of the mill, in a return line out of where the work is being done.
talking jet engines not piston.

[VH-XXX]

Wouldn't call them "high power" but a Jabiru engine has the oil temp on the side of the sump with oil pressure up near the oil filter, certainly not on a pipe. I would be of the assumption that anything with a decent sized sump would use the sump temp. No point measuring off an oil line or gallery in a piston engine with a sump. Ultimately there aren't really any oil lines to speak of anyway, unless there was an oil cooler fitted - it's all internal.

But that being said... it doesn't really matter what the temp in the gallery is, as long as the sump temp is measured and calibrated accordingly with the appropriate red-line figures. That is a design issue that you wouldn't be worried about.

[justhavingalook]

Typically for a dry sump the temp bulb is contained in a special fitting installed between the oil drain y valve and the oil pump, immediatly before entering the engine. This is so you can see that the oil cooler is doing its job and keeping the temp down. In a wet sump it is installed inside the screen immediately after the pump.

Hope this helps

[Lumps]

Some dry sump engines have two oil temp sensors, one for oil in (as justhavingalook mentioned) and one for oil out of the engine. You'll see big temperature differences between these, sometimes over 50°C. Shows how much energy is taken out by the oil cooler.

[iogrsw]

Lycomings measure the oil temp after the oil has been thru the cooler and before it enters the main gallery.

not sure about the big TCM engines but the small ones measure the temp before the oil returns to the sump.

[truth boy]

Heavily dependant on engine design, its weaknesses and strengths as far as the lubrication system go. Layout of components plays a part.Basically it would be picked up at a point that the manufacturer feels is a critical point. Could be as it enters items like bearings. Could be aft of these items. Many different designs out there.

Cheers

[Old Akro]

Oil plays a significant role in engine cooling - even in water cooled engines. In cars, generally you expect the oil temp to be 10 - 20 deg higher than water temp, ie circa 110 - 120 degC.

The problem with using the original oil temp gauges is that the calibration of them is questionable. If you are really interested, then you should try calibrating the gauge. Its pretty easy, a BBQ burner, saucepan, cheap cooking oil (less messy than car oil) and a good thermometer or thermocouple.

The gauges are typically the old bimetallic strip things as used in cars and the senders are sealed wax variable resistance devices. The unit to unit variation of both gauges and senders is significant.

If memory serves me correctly, the main problem caused by high oil temp (apart from shorter oil life due to chemical breakdown) is fatigue failure of the main & big end bearings.

If you can find it, the old Phil Irving book published by Repco, then ACL is a good easy to read reference.