Need a down and dirty method for checking your oil temp gauge for proper calibration? These Extech digital meters can be had on eBay for around $50. I have used mine to calibrate a sender by removing the sender from the engine, dropping it into a small can of water with the thermocouple taped to it, and then heating the water. I like to take the water temp up to boiling and observe the cockpit gauge versus the Extech for comparison.
In the last few days one of our guys here on the field flew his RV-7 for the first time and had a bit of a scare. After takeoff his oil temp went right up to almost 300°F! I was flying on his wing when this happened and I asked him what his oil pressure was. When he reported 90 psi, I told him it was probably indication as it's unlikely oil pressure would be that high at 300°F! I was hoping this would calm him down a little bit! He made an immediate landing and after taxiing in, I dropped the thermocouple seen here into his oil sump and read about 197°F! At least he hadn't fried his engine!
What had happened was that he had ordered an upgraded temp probe from AFS and had not entered the new code for this sensor nor the calibration values. Once we got that done it worked perfectly and now he's seeing cruise oil temps in the 190's.
An interesting fact that I noticed after playing around with my own airplane, is that the temperature reading of the oil in the sump averaged about 4.2°F above what my gauge reads. This would seem logical because the oil temp probe on the engine is just downstream from the oil cooler outlet. This would be the coolest oil in the system, with the hottest being the oil in the sump. I tried measuring my oil temp in the sump after several flights to get this average differential of 4.2°.
By the way, the first flight pictures are on my photography site below if anyone is interested.
Anyone care to guess why the oil temp is 4° cooler in the sump than ambient OAT in the photos above?
In the last few days one of our guys here on the field flew his RV-7 for the first time and had a bit of a scare. After takeoff his oil temp went right up to almost 300°F! I was flying on his wing when this happened and I asked him what his oil pressure was. When he reported 90 psi, I told him it was probably indication as it's unlikely oil pressure would be that high at 300°F! I was hoping this would calm him down a little bit! He made an immediate landing and after taxiing in, I dropped the thermocouple seen here into his oil sump and read about 197°F! At least he hadn't fried his engine!
What had happened was that he had ordered an upgraded temp probe from AFS and had not entered the new code for this sensor nor the calibration values. Once we got that done it worked perfectly and now he's seeing cruise oil temps in the 190's.
An interesting fact that I noticed after playing around with my own airplane, is that the temperature reading of the oil in the sump averaged about 4.2°F above what my gauge reads. This would seem logical because the oil temp probe on the engine is just downstream from the oil cooler outlet. This would be the coolest oil in the system, with the hottest being the oil in the sump. I tried measuring my oil temp in the sump after several flights to get this average differential of 4.2°.
By the way, the first flight pictures are on my photography site below if anyone is interested.
Anyone care to guess why the oil temp is 4° cooler in the sump than ambient OAT in the photos above?
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