diff --git a/context/open-questions.md b/context/open-questions.md
index 44deaab..d53af30 100644
--- a/context/open-questions.md
+++ b/context/open-questions.md
@@ -161,6 +161,16 @@ register.  ⚠ The audit also flags the damage-economy item as SELF-CONTRADICTOR
 (task #8 "landed" vs the kShotDamage=12 bring-up residue) — audit before reworking.
 
 ## Deferred subsystems / feeds (authentic path scoped, marked in code)
+- **Environment gravity unwired — the myomer CLIMB-heat term is inert (found 2026-07-31, #85).**
+  `Mover::localEnvironment` (MOVER.h:271) is declared and never populated anywhere in the port;
+  `GetEnvironment()->gravityConstant` is the named analog of the 1995 Mover's gravity POINTER at
+  `+0x250` (`FUN_00421e2c` does `vy -= **(+0x250)` per tick), which the myomer drive-heat
+  integrator uses for its `m·g·|vy|·dt` climb-work term.  The bridge (`BTMechMyomerMotionSample`)
+  null-guards it, so climbing currently generates no myomer heat (flat maps: moot; cavern slopes:
+  a missing cost).  EnvironmentZone resources (RES type 23) exist in BTL4.RES — wiring them (or at
+  least a constant-gravity Environment on mover birth) revives the term.  Also relevant to any
+  future airborne/jump physics (`ApplyAirResistanceAndGravity` reads the same member).
+  [[subsystems]]
 - **Revolving-door Phase 2 (true mid-mission drop-in) — PLANNED, gated on a spike**
   (`docs/REVOLVING_DOOR_PLAN.md`, 2026-07-24). Open questions before any engine work:
   (a) can an `Entity::MakeMessage` be REGENERATED post-birth (serializing current state), or
diff --git a/context/subsystems.md b/context/subsystems.md
index 957c384..d0ac3c8 100644
--- a/context/subsystems.md
+++ b/context/subsystems.md
@@ -66,7 +66,29 @@ Making a base byte-exact GROWS every subclass — they must be re-based TOGETHER
     change needs its own verification pass).
 - **WAVE 5** — Torso (aim twist/elevation; joint-I/O reconstructed; the BLH record disables torso →
   faithfully no visible twist).
-- **WAVE 6** — Myomers (mover-coupled; structural un-stub is INERT — no live mover/heat coupling).
+- **WAVE 6** — Myomers (mover-coupled; the mover feed is still inert — WAVE 6 cutover — but **DRIVE
+  HEAT IS LIVE**, #85 fix 2026-07-31, see below).
+  **✅ MYOMER DRIVE HEAT LIVE (#85, 2026-07-31) [T2].** The five Mech motion operands of the
+  drive-heat integrator `@004b8d18` were `return 0.0f` cross-family shims, so the (fully
+  reconstructed) integrator accumulated `ratio² · damageGain · 0` every tick — myomers ice cold at
+  any seek (Oracle's night-7 panel-confirmed report).  Operands re-grounded from the raw disasm +
+  the decomp and mapped to named members via the complete-TU bridge `BTMechMyomerMotionSample`
+  (mech4.cpp): `+0x1C4` vec = `localVelocity.linearMotion`; `+0x82C` vec =
+  `localAcceleration.linearMotion` (the authentic 15-ring smoothed AccelerationLastFrame);
+  `+0x20C` = `moverMass` (the collision divert's cell — the old "motion gain" label was wrong);
+  `*(+0x250)` = the environment **gravity pointer** (`FUN_00421e2c` does `vy -= **(+0x250)`/tick).
+  Physics: `heat += ratio²·(1+dmg)·[0.005·½mv² + 0.2·m·g·|vy|·dt + 0.2·m|v||a|·dt]` — kinetic work
+  + climb power + acceleration power.  The binary `fabs`es v.y (the port's old draft didn't).
+  **Authored tuning extracted from BTL4.RES** (all 18 mech variants share one record):
+  VelocityEfficiency=0.995, AccelerationEfficiency=0.8, seek gears 0.3/0.5/0.7/0.9999 rec idx 2;
+  myomer thermal profile startT=77 / degradation=1000 / failure=2000 / conductance=1.9e5 /
+  thermalMass=2.5e5.  Live-verified (solo arena, BT_MYO_LOG): standstill ≈ 0 generation, hard
+  circling drove T 77→1225 (past degradation) and the coolant loop pulled it back to ~520
+  equilibrium on slowing.  ⚠ Two carried caveats: (1) the kinetic work term has **no dt** in the
+  binary (per-tick accumulate, a 1995 fixed-frame assumption) → heat/s scales mildly with frame
+  rate; kept verbatim, field-calibrate against pod veterans.  (2) the climb term is wired but
+  inert: `Mover::localEnvironment` is never populated in the port (EnvironmentZone res type 23
+  unwired), so g reads 0 — see [[open-questions]].
   ⚠ **The registered Performance is the WRAPPER @004b8b9c, not the inner integrator @004b8d18**
   [T1, fixed 2026-07-28]. The ctor @004b8fec stores `[0x511620]` into activePerformance, and that
   pointer resolves to `0x4b8b9c`, whose first instruction is `call 0x4b0bd0` =
diff --git a/game/reconstructed/mech4.cpp b/game/reconstructed/mech4.cpp
index 038ad81..345a7fd 100644
--- a/game/reconstructed/mech4.cpp
+++ b/game/reconstructed/mech4.cpp
@@ -1606,6 +1606,36 @@ static void
 	}
 }
 
+//###########################################################################
+// BTMechMyomerMotionSample -- the five Mech motion operands of the myomer
+// drive-heat integrator @004b8d18 (issue #85), read here in a complete-Mech
+// TU and mapped to NAMED engine members per the databinding rule:
+//   binary mech+0x1C4 vec -> localVelocity.linearMotion      (|v|, v.y --
+//       the same vector the crash block's iv2 squares, operand-confirmed)
+//   binary mech+0x82C vec -> localAcceleration.linearMotion  (the published
+//       "AccelerationLastFrame" attribute, decomp-reference entity table)
+//   binary mech+0x20C     -> moverMass  (same cell the collision divert
+//       divides by -- NOT a "motion gain")
+//   binary *(mech+0x250)  -> GetEnvironment()->gravityConstant  (the 1995
+//       Mover holds a POINTER to the environment gravity: FUN_00421e2c does
+//       vy -= **(+0x250) per tick.  So the integrator's velTerm is m*g*|vy|
+//       = climb work, and the heat physics reads: kinetic energy + climb
+//       power + acceleration power, scaled by the authored inefficiencies.)
+//###########################################################################
+void BTMechMyomerMotionSample(void *mech_v,
+	float *vel_mag, float *acc_mag, float *vel_y, float *mass, float *gravity)
+{
+	Mech *m = (Mech *)mech_v;
+	const Vector3D &v = m->localVelocity.linearMotion;
+	const Vector3D &a = m->localAcceleration.linearMotion;
+	*vel_mag = (float)Sqrt(v.x * v.x + v.y * v.y + v.z * v.z);
+	*acc_mag = (float)Sqrt(a.x * a.x + a.y * a.y + a.z * a.z);
+	*vel_y   = (float)v.y;
+	*mass    = (float)m->moverMass;
+	Environment *env = m->GetEnvironment();
+	*gravity = (env != 0) ? (float)env->gravityConstant : 0.0f;
+}
+
 //###########################################################################
 // MechDeathHandler effect-spawn bridge (mechdmg.cpp calls this)
 //
diff --git a/game/reconstructed/myomers.cpp b/game/reconstructed/myomers.cpp
index ccdb385..ed13fd3 100644
--- a/game/reconstructed/myomers.cpp
+++ b/game/reconstructed/myomers.cpp
@@ -659,30 +659,62 @@ void Myomers::MyomersSimulation(Scalar time_slice)
 //
 void Myomers::MyomersDriveHeat(Scalar time_slice)
 {
-	if (!OwnerAdvancedDamage())							// FUN_004ad7d4 gate
-		return;
+	if (!OwnerAdvancedDamage())							// FUN_004ad7d4 gate (binary
+		return;											// gates the ACCUMULATE; same outcome)
 
-	Scalar velMag  = OwnerVelocityMag();				// |Mech velocity| (+0x1C4/0x1C8/0x1CC)
-	Scalar accMag  = OwnerDriveMag();					// |Mech drive vector| (+0x82C/0x830/0x834)
-	Scalar vy      = OwnerVelocityY();					// Mech +0x1C8
-	Scalar k       = OwnerMotionGain();					// Mech +0x20C
-	Scalar m       = OwnerMass();						// *Mech[0x250]
+	// #85 fix (2026-07-31): the five Mech motion operands were `return 0.0f`
+	// cross-family shims, so this integrator faithfully accumulated ratio^2 *
+	// damageGain * ZERO every tick -- the myomers stayed ice cold at any seek
+	// (Oracle's night-7 panel-confirmed report).  Now sampled for real via the
+	// complete-Mech-TU bridge (mech4.cpp), operands re-grounded against the
+	// raw disasm of @004b8d18 + the authored resource (BTL4.RES 0x0BC6 records:
+	// VelocityEfficiency=0.995, AccelerationEfficiency=0.8, gears
+	// 0.3/0.5/0.7/0.9999 rec idx 2 -- one shared tuning across all 18 mechs).
+	float velMag, accMag, vy, mass, gravity;
+	{
+		extern void BTMechMyomerMotionSample(void *mech,
+			float *vel_mag, float *acc_mag, float *vel_y,
+			float *mass, float *gravity);
+		BTMechMyomerMotionSample(owner, &velMag, &accMag, &vy, &mass, &gravity);
+	}
 
-	Scalar velComplement   = 1.0f - accelerationEfficiency;	// @0x354
-	Scalar workComplement  = 1.0f - velocityEfficiency;		// @0x350
+	Scalar velComplement   = 1.0f - accelerationEfficiency;	// @0x354 (= 0.2 authored)
+	Scalar workComplement  = 1.0f - velocityEfficiency;		// @0x350 (= 0.005 authored)
 	Scalar damageGain      = 1.0f + DamageStructureLevel();	// this[0xE0]+0x158
 
 	Scalar ratio = seekVoltage[currentSeekVoltageIndex]		// @0x330[@0x320]
 				 / seekVoltage[recommendedSeekVoltageIndex];// @0x330[@0x324]
 	if (ratio < 1.0f) ratio = 1.0f;
 
-	Scalar work = k * (velMag * velMag) * 0.5f;			// dot(v,v)*0.5 == |v|^2*0.5 (_DAT_004b8ee4)
+	// The binary fabs()es all three motion operands (the jbe/fchs pairs
+	// @4b8dd5/@4b8df0/@4b8e16); |v| and |a| are sqrt-positive already, but
+	// v.y is signed -- descending must heat like climbing, not cool.
+	if (vy < 0.0f) vy = -vy;
+
+	// Physics (operands nailed 2026-07-31): mass@0x20C, gravity=**(0x250) --
+	//   work    = 1/2 m v^2                (kinetic energy; NO dt in the
+	//             binary -- the accumulate is per-TICK, an authentic 1995
+	//             fixed-frame assumption, so heat/s scales with frame rate;
+	//             kept verbatim, field-calibrate if the pod veterans object)
+	//   velTerm = m g |vy| dt              (climb power)
+	//   accTerm = m |v| |a| dt             (acceleration power)
+	Scalar work = mass * (velMag * velMag) * 0.5f;		// dot(v,v)*0.5 (_DAT_004b8ee4)
 
 	pendingHeat /* @0x1C8 */ +=
 		ratio * ratio * damageGain *
-		( velComplement * vy * k * m * time_slice
+		( velComplement * vy * mass * gravity * time_slice
 		+ workComplement * work
-		+ velComplement * velMag * accMag * k * time_slice );
+		+ velComplement * velMag * accMag * mass * time_slice );
+
+	if (getenv("BT_MYO_LOG"))
+	{
+		static int s_n = 0;
+		if ((s_n++ % 120) == 0)
+			DEBUG_STREAM << "[myoheat] v=" << velMag << " a=" << accMag
+				<< " m=" << mass << " g=" << gravity
+				<< " ratio=" << ratio << " dmgGain=" << damageGain
+				<< " pending=" << pendingHeat << "\n" << std::flush;
+	}
 }
 
 
@@ -807,9 +839,11 @@ struct MyomersLayoutCheck
 //   The real class at 0xBC6 (ctor @004b8fec) is Myomers (the mech's artificial-
 //   muscle drive); the factory built an Actuator RECON_SUBSYS stub.  alloc 0x358.
 //   The subsystem constructs (resolves its Generator + builds the seek-voltage
-//   gear table) and ticks its real Performance, but is currently INERT w.r.t.
-//   locomotion/heat (no-op mover feed + the OwnerAdvancedDamage()==False sim gate)
-//   -- so it cannot regress the gait/drive.  Authentic coupling = a follow-up.
+//   gear table) and ticks its real Performance.  DRIVE HEAT IS LIVE (#85 fix
+//   2026-07-31: the motion operands are sampled from the real Mech).  Still
+//   inert: the LOCOMOTION coupling (no-op mover feed -- speedEffect is computed
+//   but nothing consumes it; WAVE 6 cutover) and the climb heat term (the
+//   environment gravity is unwired in the port, so g reads 0).
 //===========================================================================//
 Subsystem *CreateMyomersSubsystem(Mech *owner, int id, void *seg)
 {
diff --git a/game/reconstructed/myomers.hpp b/game/reconstructed/myomers.hpp
index f7d9562..c7607a0 100644
--- a/game/reconstructed/myomers.hpp
+++ b/game/reconstructed/myomers.hpp
@@ -331,11 +331,10 @@ class Mech;
 		Scalar	OwnerBaseSpeed() const		{ return 1.0f; }	// Mech +0x34C (neutral)
 		Scalar	OwnerMaxSpeed() const		{ return 0.0f; }	// Mech +0x7A0
 		void	SetOwnerMaxSpeed(Scalar)	{ }					// no-op (real: write Mech top speed)
-		Scalar	OwnerVelocityMag() const	{ return 0.0f; }	// |Mech velocity|
-		Scalar	OwnerDriveMag() const		{ return 0.0f; }	// |Mech drive/accel|
-		Scalar	OwnerVelocityY() const		{ return 0.0f; }	// Mech velocity.y
-		Scalar	OwnerMotionGain() const		{ return 0.0f; }	// Mech +0x20C
-		Scalar	OwnerMass() const			{ return 0.0f; }	// *Mech +0x250
+		// (The five drive-heat motion shims are GONE -- #85 fix 2026-07-31:
+		// MyomersDriveHeat samples the real Mech via the complete-TU bridge
+		// BTMechMyomerMotionSample (mech4.cpp).  The mover-feed trio below is
+		// still the WAVE-6 remainder.)
 		// FUN_004ad7d4 [T1] -- the SAME player+0x260 heat-model experience gate
 		// as HeatSink::HeatModelActive() (the "advanced damage" name was a
 		// misread; the old `return False` stub kept movement heat off for