When his Skylane’s engine monitor readings went crazy-high, Frank called Savvy’s 24/7 breakdown assistance hotline for help.
“I just flew my Cessna 182 from Kansas City to St. Louis to drop off a passenger there,” Frank Annecchini told the Savvy Breakdown Assistance Hotline operator. “Everything was normal. But after I dropped off my passenger and taxied back out for takeoff, my oil temperature was above 390℉ and all my CHTs were above 440℉. I taxied back to the parking area, shut down the engine, and checked the dipstick. The oil level and color look normal. But even with the engine shut down, the oil temperature is 330℉ and the CHTs are around 420℉. I’m not sure what to do.”
The operator dutifully transcribed this onto a Savvy breakdown ticket and asked Frank for some additional information. She learned that the plane was a 1963 Cessna 182F, it was AOG at Spirit of St. Louis airport (KSUS), and obtained Frank’s cell phone number. She transcribed this info to the ticket, too.
“Expect a callback from a Savvy technician within 15 minutes,” the operator told Frank.
Savvy’s Team Approach
About 10 minutes later, Savvy’s on-call account manager, Tom Cooper A&P/IA, called Frank back, but the call rolled to voicemail so Tom left a message.
While waiting for a return call from Frank, Tom decided to bring another Savvy account manager, James Watson A&P/IA, onto Frank’s ticket. James owns and operates Watson Aero LLC in Louisville, Georgia, a superb aircraft engine overhaul shop, and serves as one of several engine specialists on Savvy’s technical team.
James succeeded in reaching Frank via cell phone. He went over all the information on Frank’s ticket, asked some questions, and learned that Frank’s 61-year-old airplane was equipped with a very modern and capable digital engine monitor, an Electronics International CGR-30P.
Differential Diagnosis
Now, James knew that modern digital engine monitors like the CGR-30P are usually extremely accurate. Yet the oil temperature readings that Frank was reporting were highly suspect. If the oil was really at 330℉ or 340℉, it would be “caramelized” and look dark and smell awful. But Frank had checked the dipstick and found the oil looked and smelled quite normal.
The CHTs Frank was reporting in the 420℉ and 440+℉ range would have been abnormally high but possible had the airplane been at full takeoff power – CHT red-line for the Continental O-470-R is 460℉ – but 440+℉ was clearly impossible with the engine at taxi power, and 420℉was even more impossible with the engine shut down.
When an instrument reading violates the laws of physics, it has to be wrong. Clearly, Frank’s fancy digital engine monitor was lying to him! But why?
If the engine monitor was displaying just one or two temperatures that were crazy, the problem might have been a bad oil temperature or CHT probe – although the thermocouple probes used by most modern engine monitors almost always fail in the low direction, not the high direction. But Frank was quite certain that all six CHTs were showing 420℉ or higher, and he was pretty sure that all of the EGTs looked higher than normal, too, although he really hadn’t focused on them.
James mulled this over and then told Frank that he could think of only one possible explanation for what Frank was seeing on his CGR-30P.
Prime Suspect: The EDC
James knew that the CGR-30P uses a remote-mounted module called the Engine Data Converter (EDC) to take the millivolt analog signals from the thermocouple temperature sensors and convert them to digital temperatures that are then sent via a serial data link to the panel-mounted CGR-30P display.
James was confident that the reason the CGR-30P was lying about all those temperatures had to be an analog problem and therefore something related to the EDC. Although it could have been an internal EDC failure, James suspected that a bad (high-resistance) ground connection between the EDC and the airframe was the most likely explanation.
James asked Frank if he could locate the EDC, explaining that it was a small 4-by-6 inch metal box that is usually mounted somewhere on the cockpit side of the firewall and has several thick bundles of wires connected to it.
Frank stuck his head under the instrument panel and looked around. “I’m pretty sure I found it!” Frank told James excitedly.
“Try wiggling the plugs that connect to the EDC and make sure they’re all securely attached. Also, check the mounting screws and make sure the EDC is firmly attached to the firewall.” Frank proceeded to poke, prod, and wiggle everything in the vicinity of the EDC.
The Smoke Test
“Okay, now turn on the master switch, let the CGR-30P boot up, and then let me know what temperature indications you see.”
Frank followed these instructions and – lo and behold – the oil temperature and CHTs were nice and cool.
James suggested that Frank should start the engine, taxi out, perform a normal pre-flight runup, and if the temperature readings still looked normal, take off and fly home to Kansas City. “If the temperatures are still wonky, taxi to parking and call me back.”
The temps remained normal. Frank had an uneventful flight home, and reported this to James on the ticket. James suggested that Frank have his regular mechanic or avionics technician double-check the EDC connections just to be on the safe side.
Frank’s experience is not at all unusual. About 50% of the time one of our Savvy clients calls the toll-free 24/7 Savvy Breakdown Assistance Hotline with an AOG issue, we are able to diagnose and resolve or work around the problem and get the client back in the air quickly and safely without involving a local shop or mechanic. (The rest of the time, we provide a pinpoint diagnosis and then work with a local mechanic to get the problem resolved.)
Think of Savvy’s 24/7 fast-response breakdown assistance service as “AAA for GA.” This service is part of every Savvy plan, even our lowest-tier SavvyBasics plan that costs just $99/year for a piston single or $149/year for a piston twin.
Do you really want to leave home without it?