Oil Temp less than 160F

Notatestpilot

Notatestpilot

Pre-takeoff checklist
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Notatestpilot
I have an O320 in my RV, swinging a fixed pitch prop…
The OAT today was 34 F degrees.
I have the face of my oil cooler blocked off and my oil temp is usually in 170 to 180F range.
However, today it just hovered between 150 to 160.
I thought maybe it was the temp gage, but when I throttle down the temp did decrease from 150 and lower.
Could it be the gage or the sending unit?
Or maybe Vernatherm?
 
Check with an IR thermometer?
 
Is that OAT low for your area? I only get to 180-185 in the hot summer days. My typical winter oil temp is 150-170 with both the bottom and the baffle opening for the oil cooler blocked off. I take the baffle winter plate off for the summer. My last engine was always 195-210, hotter in the hottest summer days. These engines can be very different for oil temps. I use an engine dehydrator now due to the low oil temps.
 
Bell206 said:
Is this the 1st time you noticed this with similar conditions? Has it repeated itself on subsequent flights?
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Today's OAT is not low for my area; Southern Illinois...
We've had lower earlier in the season; high 20's F.
When I notice this , I turned around the landed back at my home airport.
I then completed blocked off the face of the oil cooler.
I put the cowling back on, and went back up for another flight. Same thing, the needle didn't increase past 155deg F. My oil pressure was good/steady (70+psi), so I figure it's the temp gauge or sensor. To be safe, I flew it at 2200 RPM. After an hour, came back home and landed. This temp gauge and sensor was replaced just short of 10 years ago. I have about 450 hours on this new gauge/sensor. Its the no longer made 2 1/4" gauge that Van's use to carry in their catalog.
Any thoughts/suggestions?
Thanks!
 
Notatestpilot said:
Any thoughts/suggestions?
Click to expand...
So if I understand you correctly the aircraft has been indicating 170-180 up until the last 2 flights where it only indicated 150-160 even with the cooler blocked? Since the change happened between flights the vernatherm maybe stuck open for some reason? You could pull it and see if it is fully seated at ambient temps. I usually opt to check the indicating system accuracy first based on my experiences but in this case you might get lucky. If the vern is seated and looks good then move onto the indicating system checks.
 
How did you "completely block off the face of the oil cooler?"

You can remove the probe and submerge in boiling water. With the master on, the gauge should be active. Not familiar with the engine compartment configuration of an RV, but you may be able to do this in situ. You will need to ground the probe's body to the airframe. Extenders will be useful.

S.IL is at about 500 MSL. Use this calculator https://www.thermoworks.com/bpcalc/ to determine your water's expected boiling point. Altitude and barometric pressure are easily available.
Example, 500 MSL, 29.65 inHg, yields 210.68 F.
Leadville, CO (KLXV), 9934 MSL, 29.79 inHg, yields 193.5 F
 
I think you’re overthinking it. 150F-160F is pretty typical in temperatures like that. Was that OAT reading on the ground or in the air? I would not be concerned, especially with an O320 that doesn’t produce a lot of heat in general.
 
RyanB said:
I think you’re overthinking it. 150F-160F is pretty typical in temperatures like that. Was that OAT reading on the ground or in the air? I would not be concerned, especially with an O320 that doesn’t produce a lot of heat in general.
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Close ... seems Lycoming wants it slightly higher:

"The desired oil temperature range for Lycoming engines is from 165˚ to 220˚ F."

https://www.lycoming.com/content/operating-cold-weather

It would be a concern if what the OP is seeing is a change from what is normally expected under similar conditions.
 
Bell206 said:
So if I understand you correctly the aircraft has been indicating 170-180 up until the last 2 flights where it only indicated 150-160 even with the cooler blocked? Since the change happened between flights the vernatherm maybe stuck open for some reason? You could pull it and see if it is fully seated at ambient temps. I usually opt to check the indicating system accuracy first based on my experiences but in this case you might get lucky. If the vern is seated and looks good then move onto the indicating system checks.
Click to expand...
Here’s an update on my troubleshooting.
I verified using boiling water, and the sensor/gauge indicated 180F.
I’ve now removed the Vernatherm.
I placed the Vernatherm in boiling water and it extended a quarter of an inch; 0.25”.
Now I’m a bit puzzled. Everything seems to check out functionally.
Any ideas?
 
Exactly. So 180 on that gauge is actually around 212. So a reading of 150 is actually around 180 actual oil temp.

Sounds like the sensor or gauge is having an issue.
 
Notatestpilot said:
I verified using boiling water, and the sensor/gauge indicated 180F.
Click to expand...
As noted above seems we have an indicating problem. The vern looks good. So depending on the type oil temp indicator and probe you have installed might be able to see which item is bad. But the 1st thing to check is the temp system wires and connections for serviceability. Is the indicator digital or analog? Does the temp probe have 2 wires? The brand name/model numbers would be even better.
 
How did you test the sensor? Details matter. Any resistance in the circuit will change the reading. The thermistor resistance decreases as temperature goes up. Not sure how the RV is wired, but in my Cherokee, a single wire runs from gauge to sensor, and ground return is through the engine block. Check the positive and ground connects on the gauge. Check the connector crimp on the sensor wire. Sometimes insulated wires will break INSIDE the insulation sheath due to vibration induced work-hardening.

What brand/model sensor and gauge is installed?
 
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