Engine Run-Up

Where these numbers come from. Lycoming Service Instruction No. 1132B, “Magneto Drop-off”, revised 18 June 2010, page 2: drop-off must not exceed 175 RPM and must not exceed 50 RPM between magnetos. It covers all Lycoming opposed-series aircraft engines with magnetos, which is the engine class this trainer represents. These are the engine manufacturer's figures.

There is no FAA number. The Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C, 2023) p. 7-15 says only “The permissible decrease is listed in the AFM or POH.” The Airplane Flying Handbook (FAA-H-8083-3C) ch. 2 p. 2-21 asks only that magneto operation be “within limits”. Published limits also vary by installation — S.I. 1132B itself notes 100 RPM for the O-290-D2 and 200 RPM for helicopter installations.

Two disclosures. This trainer checks at 1,700 RPM, an airframe-checklist convention; Lycoming publishes the 175-RPM figure at approximately 1,800 RPM. And the 20-RPM floor this sim uses for “no drop” is a sim convention — no source publishes a minimum acceptable drop.

Oil temperature in this trainer is an indication and nothing else: nothing is decided by it — no check, hint or debrief item compares it to anything, and the instrument-check step reads it out without grading it. The oil warms toward its running target with a 5-minute time constant and the gauge lags the oil by a further 1-minute time constant, so the needle barely moves in the first half-minute and takes about three minutes to reach the bottom of the green arc. A shut-down engine gives its heat back over a 15-minute time constant. All three are this trainer's conventions — no retrieved source publishes a warm-up or a cool-down rate for any piston engine. What is published is the order of magnitude: FAA PHAK (FAA-H-8083-25C, 2023) p. 7-17 says changes in oil temperature occur slowly, and that after starting a cold engine it may take several minutes or longer before the gauge shows any increase at all; FAA AFH (FAA-H-8083-3C, 2023) p. 2-21 says taxiing to the run-up position usually allows enough time to reach at least minimum operating temperature.

The running target of 170–180 °F sits inside Lycoming's published Desired average oil inlet temperature — 180 °F above 60 °F ambient, 170 °F and 160 °F in colder air — and the 245 °F red radial is Lycoming's published Maximum, though the O-320 manual drops that maximum to 225 °F and 210 °F in its two coldest ambient rows. The green arc starts at 100 °F because the FAA's illustrative gauge does (AMT-P FAA-H-8083-32B p. 10-22, Figure 10-36); the FAA calls that low end the minimum oil temperature permissible for ground checks or flight, and says on p. 10-25 that those illustrative figures have no general application. Lycoming publishes 140 °F as the minimum for continuous operation in its O-360, O-320-H and O-235/O-290 manuals and omits it from the O-320 manual this sim cites — we show you that disagreement rather than pick a side.

Because this trainer runs a whole run-up in well under a minute, the needle will normally still be below the green arc when you finish. That is the honest consequence of a slow warm-up and a fast lesson, and it is not this sim's place to tell you the engine is warm enough: Lycoming's own test is that the engine is warm enough for take-off when the throttle can be opened without it faltering (O-320 p. 3-3), and the AFH says the minimum oil temperature, where one exists, is in the AFM/POH. This sim grades neither.

Lycoming O-320 Operator's Manual, 3rd Ed. (Part No. 60297-30, October 2006), p. 3-2: “Open throttle approximately ¼ travel.” Some Cessna 172 Owner's Manual checklists instead read “Throttle — OPEN 1/8 INCH.” Those are different measurements and we cannot tell you whether they agree. Your airplane's POH governs. This sim shows the throttle as a percentage of lever travel and accepts 10–40 % — that percentage and that band are sim conventions, not checklist numbers.

Cold-start priming: Lycoming O-320 p. 3-2 says a hot engine is started by “omitting the priming step”, but neither it nor any FAA handbook defines “hot” — not by a temperature, not by an instrument reading, not by a clock. The nearest published guidance is FAA AMT-P (FAA-H-8083-32B, 2023) p. 10-21, which says an engine shut down for only a short time may not need priming, and that the heat deciding it sits in the carburetor and the fuel, not in the oil. So this sim decides hot-versus-cold on how recently the engine ran: an engine that has run in this session and been stopped for less than 10 minutes of sim time is treated as hot and starts with no primer stroke. Ten minutes is this trainer's convention and has no published basis — no source quantifies “a short time”. Indicated oil temperature decides nothing here. An earlier version of this sim gated the start on oil above 100 °F; that threshold is gone, and so is the fast warming constant that existed to make it reachable.

This trainer models the oil pressure indication as electrically powered, so it reads nothing with the master switch off. That matches FAA SAIB CE-19-01 R1 (6 December 2022), which states that on the Cessna 172R/S “the oil pressure gauge/indicator is driven by a separate dedicated pressure transducer.” Other airplanes — including many older cluster-gauge trainers — use a direct-reading Bourdon-tube gauge plumbed to an oil line, which needs no ship power (FAA-H-8083-32B, ch. 6, pp. 6-8 to 6-9). We do not model yours; check your AFM/POH.

The engine is unaffected either way: the magnetos need no ship power at all — “A magneto uses a permanent magnet to generate an electrical current completely independent of the aircraft’s electrical system” (FAA-H-8083-25C, 2023, p. 7-15). An unpowered gauge is shown flagged UNPWR rather than at zero, because a zero from a dead instrument is not evidence of anything, and this sim will not grade one.