CamTom12
Registered User
Huntsville, AL
This has actually happened twice. Both times in hot weather. In OATs below ~70 deg F oil temps are usually ok. The first time was a year ago, the last time was on Tuesday.
Oil temps pegged right at the redline (245) and held there for a while. 2200 RPM and 120 mph at ~6500 and 60 deg F oat. This was after the climb-out (which I did at full throttle, full rich, and 110 mph). After 10-15 minutes, temps dropped rapidly to ~200. This last time I saw the temp swing back and forth between 180 and 220 a few times (rapidly, transitioning in 1-2 seconds). On that same flight I descended from 6500 (oat ~60 deg F) to 1500 (oat ~90) at 500 fpm (probably something around 1800-2000 rpm and 130-140 mph). Oil temp dropped gradually to 165 and stayed there until after touchdown when it spiked and held back to 200 deg. CHTs were between 330-380 at cruise power and 280-330 in the descent.
This week I replaced the vernatherm as part of the annual condition inspection (in accordance with the new Lycoming SI). The flight described above was the first flight after. I also replaced all the rubber baffle seals as part of the inspection. Manometer test is yet to happen, but they look WAY better than before. I also sealed around the oil cooler better.
Normally, it's not unusual to see temp swings of 40 deg or more (though usually they max out below 220) so I keep oil temps in my scan because of this. When it gets to 225 (unusual) I start decreasing power, descending, and looking for a place to land.
I've been assuming it was an indicating problem because of how fast the indication swings (I'm still going to test the indicating system with a hot-plate, a pan of oil, and a good thermometer), but the last time it happened I noticed that the oil pressure was down to 65psi when the temps indicated high. Normally its near 80-85 psi. Plus digging around the oil diagrams over the past two days it looks like the oil temp sender measures oil temps before it gets routed through the engine, which would mean after the oil cooler. If I understand it right, it would mean that if the cooler were isolated from the engine, then the flow was resumed, it could cause a rapid change in oil temps as read by the oil temp sender.
My current theory (pending a successful test of the indicating system) is that there's something hanging up in the path between the engine and the oil cooler that's preventing the oil from going to and from the cooler. The brand new vernatherm which is showing the same symptoms as the old one so I don't think its that (I can test it when I test the indicating system to be sure). This is on a Lycoming spin-on adaptor (p/n 77852, I think).
When I go to troubleshoot this weekend I want to maximize what I look at, since I'll likely have to drain a brand new oil change and am trying to get it all checked out at once.
What else could cause symptoms like these? What else might cause what seems like an intermittent blockage of the oil cooler from the engine? What would happen if there was also a viscosity valve (type 1 bypass) installed with my vernatherm and that viscosity valve was malfunctioning? Could it cause symptoms like these? Any other ideas I should check out?
Oil temps pegged right at the redline (245) and held there for a while. 2200 RPM and 120 mph at ~6500 and 60 deg F oat. This was after the climb-out (which I did at full throttle, full rich, and 110 mph). After 10-15 minutes, temps dropped rapidly to ~200. This last time I saw the temp swing back and forth between 180 and 220 a few times (rapidly, transitioning in 1-2 seconds). On that same flight I descended from 6500 (oat ~60 deg F) to 1500 (oat ~90) at 500 fpm (probably something around 1800-2000 rpm and 130-140 mph). Oil temp dropped gradually to 165 and stayed there until after touchdown when it spiked and held back to 200 deg. CHTs were between 330-380 at cruise power and 280-330 in the descent.
This week I replaced the vernatherm as part of the annual condition inspection (in accordance with the new Lycoming SI). The flight described above was the first flight after. I also replaced all the rubber baffle seals as part of the inspection. Manometer test is yet to happen, but they look WAY better than before. I also sealed around the oil cooler better.
Normally, it's not unusual to see temp swings of 40 deg or more (though usually they max out below 220) so I keep oil temps in my scan because of this. When it gets to 225 (unusual) I start decreasing power, descending, and looking for a place to land.
I've been assuming it was an indicating problem because of how fast the indication swings (I'm still going to test the indicating system with a hot-plate, a pan of oil, and a good thermometer), but the last time it happened I noticed that the oil pressure was down to 65psi when the temps indicated high. Normally its near 80-85 psi. Plus digging around the oil diagrams over the past two days it looks like the oil temp sender measures oil temps before it gets routed through the engine, which would mean after the oil cooler. If I understand it right, it would mean that if the cooler were isolated from the engine, then the flow was resumed, it could cause a rapid change in oil temps as read by the oil temp sender.
My current theory (pending a successful test of the indicating system) is that there's something hanging up in the path between the engine and the oil cooler that's preventing the oil from going to and from the cooler. The brand new vernatherm which is showing the same symptoms as the old one so I don't think its that (I can test it when I test the indicating system to be sure). This is on a Lycoming spin-on adaptor (p/n 77852, I think).
When I go to troubleshoot this weekend I want to maximize what I look at, since I'll likely have to drain a brand new oil change and am trying to get it all checked out at once.
What else could cause symptoms like these? What else might cause what seems like an intermittent blockage of the oil cooler from the engine? What would happen if there was also a viscosity valve (type 1 bypass) installed with my vernatherm and that viscosity valve was malfunctioning? Could it cause symptoms like these? Any other ideas I should check out?
