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Oil Temp Question


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I've fought (and, pretty much given up) high oil temps since I bought my plane 3 years ago.  Typically run over 200 in cruise; maybe 210 on hot days.  In climb I can see 220-230.  This is the reading on my Insight G3.  The ship's factory gauge reads toward the high side, but really hard to quantify.

I just realized that the temp sender for the factory gauge is back near the oil filter/vernatherm, while the G3's sensor is at the front of the engine.  Does anyone know if that location is going to indicate a higher temp?  And, if so, how much higher?

For those of you with both factory and engine monitor temp gauges, how do they correlate?  E.g., if the engine monitor shows 180, is the factory gauge mid-scale, or?

Thanks!!

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Find a diagram of the Io360’s oil system...

You will probably see two identical oil paths... left and right...

Often, if the ship’s gauge is in the front on one side.... there is an identical port available on the right side in a mirror location...

The mirrored locations will probably see similar Ts and Ps... there are several locations where an OilT sensor can be put... but surely a different location can mean different Ts... that is why the ship’s OilT sensor always goes in the same spot...

Often, newer POHs have a diagram of how the oil flows through the engine block, down to the bearings... including all the details of where things are like the vernatherm and the oilP regulator...

PP thoughts only,

-a-

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5 hours ago, MikeOH said:

Typically run over 200 in cruise; maybe 210 on hot days.

Why would this be bad for oil temperature? I'd figure it is close to optimal - boils all the water right out the breather while not breaking down the lubricating properties yet (that would require 300F+ for mineral oil, if I recall correctly).

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8 hours ago, tmo said:

Why would this be bad for oil temperature? I'd figure it is close to optimal - boils all the water right out the breather while not breaking down the lubricating properties yet (that would require 300F+ for mineral oil, if I recall correctly).

The oil temperature varies at various points within the engine and the gauge is not at the point of highest temperature.

Ben Visser

12/10/2004 


A few issues back, my good friend Paul McBride was asked what was the best oil temperature for an aircraft engine (Just what is normal? Oct. 15 issue). Since then, I have received a few questions about the same subject, but from the lubricant perspective.

Although I hate to admit it in public, Paul was right. The best oil temperature for most opposed, certified aircraft engines is about 180°F under normal cruise conditions. (Higher oil temperatures can be expected during climb-out.)

This is based on several pieces of data. First, the oil throughout the engine is at various instantaneous temperatures. Usually the hottest oil in the engine is the oil coming off the underside of the piston.

We have determined that on most non-turbocharged engines, this instantaneous oil temperature is usually about 50° hotter than the temperature of the oil going into the engine. If we add the 50° to an engine oil temperature of only 160°, we see that the oil never gets over the 212° mark, which is the boiling point of water. By running at 180° during cruise, the oil should be hot enough to boil off the normal condensation in a one-hour flight.

On the high end, the maximum preferred oil temperature is around 200°. This guideline is based on data that show the instantaneous temperature of the oil coming off the pistons for many turbocharged piston engines is about 75° above the temperature of the oil going into the engine. This means that if you are running an oil temperature of 240° during cruise, the oil is actually reaching 315° at some point in the engine. This is OK for a short time during climb-out, but if your engine operates for extended periods at this temperature, it can lead to coking and an increased level of deposits in your engine.

Remember that these are just guidelines and there are some exceptions. For example, if you have an aircraft that does not have a CHT or EGT gauge, the oil temperature is the only temperature indication that you have. Say that your engine oil temperature normally runs at 160° under cruise conditions on an 80° day. If it suddenly starts to run at 180° under the same conditions with no other change being made to the aircraft, this could be an indication of one or more cylinders running too hot or some other problem. You should check to make sure that your oil temperature is not only at the proper level, but also that it is consistent under the same conditions.

A final point is one that Paul also noted, and that is oil temperature gauge calibration. Many of the airplanes flying today have gauges that have not been checked in 20 or 30 years. In addition, many of the gauges just have a green band from around 100° to 240°. I would recommend that you remove your oil temp sensor and place it in a container of oil or water. Place the container on a hot plate with a good referenced thermometer in the liquid to check the temperature. Now heat the container up to 180°. When the temperature in the container stabilizes, check the gauge. I also recommend that you paint a small mark on the face of your gauge so that you can easily see where your oil temp is relative to your 180° mark. Now you can start worrying with confidence about how to get your oil temp up to 180° in the winter and/or down to 180° in the summer.


Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985. You can contact him at Visser@GeneralAviationNews.com.


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13 hours ago, PT20J said:

My M20J EDM 700 oil temp (front sender) reads about 8 deg higher than the factory gauge (rear sender). I usually run about 200F +/- 5F during cruise depending on OAT and power setting.

Skip

Edit: The 200 number is for the EDM 700 temp.

That's about what mine reads on my F with the sender in the factory location with an EDM 900. 

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