Mooney M20K 231/252/Encore (1979-1998)

The Mooney M20K 231 is the turbocharged sibling of the M20J 201 -- the same redesigned long-body airframe with a Continental TSIO-360-GB (later -LB) turbocharged engine producing 210 HP, introduced in late 1978 for the 1979 model year. It was Mooney's first turbocharged single since the 1960s production Mustang-adjacent experiments, and the "231" name is contemporary marketing shorthand for its performance, not a certificate designation -- the FAA lists it, the 252 and the Encore all as "Model M20K" on one certificate section.

889 airframes (S/N 25-0001 through 25-0889) were built in this early, manual-wastegate configuration before Mooney moved to the automatic-wastegate 252 in 1986. Per AOPA's March 1980 report, 1980 alone saw 264 Model 231s delivered against 175 M20J 201s -- the 231 was, for a period, Mooney's best-selling model.

The 231's defining operational trait is its manual wastegate: the pilot must monitor manifold pressure and adjust the wastegate control through climb and altitude changes, and mismanagement risks an engine-damaging over-boost. This is the single biggest thing that separates flying a 231 from flying a 252 or an Encore, and it is the reason this page and a future 252/Encore page should not be merged even though the certificate treats them as one model.

The M20K 231 with manual wastegate is the most challenging to operate -- the pilot must constantly manage wastegate position to avoid over-boost during climb and altitude changes. The 252 and Encore introduced automatic wastegates, eliminating this workload.

A common modification: convert 231 to manual-wastegate-friendly via Merlyn Black Magic or Turboplus Intercooler kits. Cost: $8,000-$15,000 installed. Significantly improves operability and resale value.

This catalogue's convention for turbocharged airplanes is to store the high-altitude cruise figure, because that is what the turbocharger is bought for. The 231's headline cruise_speed_ktas (192 kt) is AOPA's own 75%-power, 24,000-ft row -- the certificate's stated maximum operating altitude for this airplane (S/N 25-0001 thru 25-0999, which covers the entire 231 block). At lower altitudes the same source gives 170 kt at 10,000 ft / 75% power, and at lower power settings 179 kt (65%) and 162 kt (55%) at 24,000 ft -- the turbo's whole appeal is that the airplane is nearly as fast at FL240 as at 10,000 ft, unlike a normally-aspirated Mooney whose true airspeed falls off with altitude as manifold pressure bleeds away.

No fuel burn or range figure is stored for this cruise condition. AOPA's own words -- "an average fuel burn of less than 13 gph" -- describe the airplane's economy generally, not the specific 75%/24,000 ft cell, so storing it against fuel_burn_gph would violate the one-row rule this catalogue holds to. Owners flying the 231 at high cruise power report burns in the 13-15 gph range in practice; treat that as pilot lore, not a sourced figure. Likewise AOPA's own range figures (928-987 nm depending on power and altitude) are real and are quoted in the saved passage, but this catalogue does not accept range from press sources under any circumstance (rule 29) -- a correctly sourced range figure needs the airplane's own POH, which was searched for and not found readable this session.

Fuel capacity has an internal ambiguity worth knowing about. The certificate splits it at S/N 25-0447: "72.0 gal." for the first 446 airframes with no stated usable figure, "75.6 gal. usable" for S/N 25-0447 and on. This page stores 75.6 because it is the only figure the certificate itself labels usable -- an early-serial 231 (roughly half the fleet) may carry somewhat less usable fuel than this page states, and a buyer of a pre-25-0447 airframe should confirm the actual figure against that airplane's own POH.

M20K 231 (TSIO-360-GB1, 210 HP, 75.6 usable gal):

Useful load 1,100 lb with 75.6 gallons usable makes the 231 a genuine two-to-three-adult, long-range airplane, tighter than the naturally-aspirated M20J on a four-adults-full-fuel basis (both airframes share the same short cabin) but with a materially higher service ceiling and better high-altitude true airspeed.

• Flight Training (2): Not a trainer -- the manual wastegate adds workload no primary student needs, on top of the usual Mooney Johnson-bar complexity.
• Backcountry (1): Low-wing retractable, no business off pavement.
• Business Travel (9): The high-altitude cruise capability is a genuine business asset -- flight-planning above weather that a normally-aspirated single cannot top.
• Aerobatics (1): Not certified.
• Cross-Country (10): The turbo's whole reason to exist. 192 kt at 24,000 ft with real range (AOPA's own figures run 928-987 nm, though not stored here) makes the 231 a serious point-to-point airplane.
• Cargo Hauling (3): Modest useful load (1,100 lb) once four adults and bags are aboard, same limitation as every M20 short-body.
• Local Fun Flying (6): Manual wastegate management is arguably enjoyable to some pilots and a chore to others; scored down slightly from the naturally aspirated Mooneys for that reason.
• Surveying (4): Low-wing visibility limitation, and the turbo's advantages are wasted at survey altitudes.

Parts availability "fair" -- shares the general Mooney parts-support picture (LASAR is the primary aftermarket source) with the added complexity of turbocharger and wastegate hardware that a non-turbo-Mooney shop may not stock. Mechanic familiarity "specialist" -- Mooney-specific knowledge plus turbo experience is genuinely useful, not just nice to have, given the over-boost risk described above.

Price bands below are retained from the prior catalogue pass and were not independently verified this session -- see the validator_exempt entries and raw/market/market-mooney-late-m20-2026-09-08.md for what was attempted.

For context only (1980 dollars, not adjusted): AOPA's March 1980 spec panel lists the 231's base price as $57,775 and $105,770 as tested with a full avionics/oxygen/radar/deice package.

Universal Mooney pre-buy items apply (Johnson-bar/electric gear rigging, elevator balance weight, fuel bladder deterioration). 231-specific:

1. Wastegate condition and operating history -- the single biggest pre-buy item on this specific airplane. Ask directly about over-boost incidents; they are the leading cause of premature TSIO-360 top-end wear on the manual-wastegate 231.
2. Turbocharger shaft play and oil seepage -- inspect at annual; turbo overhaul runs roughly $5,000-$8,000 (not independently priced this session).
3. Cylinder condition -- turbocharged Continentals run hot; a full borescope and CHT/EGT trend review is standard practice on any 231 pre-buy.
4. Intercooler retrofit history, where present -- verify STC compliance and plumbing quality.
5. Cool-down discipline -- inconsistent post-flight turbo cool-down shortens turbo life; ask for the owner's habits, not just the logbook.

Retractable high-performance turbocharged single. Typical hull premium $2,000-$3,500/year depending on pilot experience and time-in-type; complex/HP and turbo-transition training is a standard underwriting requirement for a pilot new to the type. (Carried from the page's prior content -- not independently re-verified this session.)