diff --git a/docs/circular-deps.txt b/docs/circular-deps.txt
index 8f53dd8..e9106fa 100644
--- a/docs/circular-deps.txt
+++ b/docs/circular-deps.txt
@@ -1,5 +1,5 @@
 # Circular Dependencies
-Generated: 2026-06-08T10:56:12.135Z
+Generated: 2026-06-08T11:14:13.243Z
 Found: 1 circular chain(s) — these MUST be fixed before modifying involved files.
 
 1. 1) stores/golem-combat-actions.ts > stores/golem-combat-helpers.ts
diff --git a/docs/dependency-graph.json b/docs/dependency-graph.json
index 5e1e4aa..25b3a71 100644
--- a/docs/dependency-graph.json
+++ b/docs/dependency-graph.json
@@ -1,6 +1,6 @@
 {
   "_meta": {
-    "generated": "2026-06-08T10:56:10.139Z",
+    "generated": "2026-06-08T11:14:11.296Z",
     "description": "Import dependency graph for src/lib/game. Keys are files, values are arrays of files they import.",
     "usage": "To find what a file affects, search for its path in the VALUES. To find what a file depends on, look at its KEY entry."
   },
diff --git a/docs/project-structure.txt b/docs/project-structure.txt
index 897d32d..20ca0a3 100644
--- a/docs/project-structure.txt
+++ b/docs/project-structure.txt
@@ -392,6 +392,7 @@ Mana-Loop/
 │   │   │   │   ├── golem-combat-actions.ts
 │   │   │   │   ├── golem-combat-helpers.test.ts
 │   │   │   │   ├── golem-combat-helpers.ts
+│   │   │   │   ├── golem-combat-maintenance.test.ts
 │   │   │   │   ├── golemancy-actions.ts
 │   │   │   │   ├── golemancy-combat.test.ts
 │   │   │   │   ├── index.ts
diff --git a/src/components/game/tabs/golemancy/GolemancyComponents.test.ts b/src/components/game/tabs/golemancy/GolemancyComponents.test.ts
index bab47c7..ff7cf61 100644
--- a/src/components/game/tabs/golemancy/GolemancyComponents.test.ts
+++ b/src/components/game/tabs/golemancy/GolemancyComponents.test.ts
@@ -83,10 +83,14 @@ describe('computeGolemStats', () => {
     // Total summon cost includes all components + enchantments
     expect(stats.totalSummonCost.length).toBeGreaterThan(0);
 
-    // Upkeep = core.manaRegen * 2 per hour
-    expect(stats.upkeepCostPerHour.length).toBe(1);
-    expect(stats.upkeepCostPerHour[0].amount).toBe(6.0); // 3.0 * 2
+    // Upkeep = core.manaRegen * 2 per hour, split across selected mana types
+    expect(stats.upkeepCostPerHour.length).toBe(3); // crystal, metal, fire
+    expect(stats.upkeepCostPerHour[0].amount).toBe(2.0); // 6.0 / 3
     expect(stats.upkeepCostPerHour[0].element).toBe('crystal');
+    expect(stats.upkeepCostPerHour[1].amount).toBe(2.0);
+    expect(stats.upkeepCostPerHour[1].element).toBe('metal');
+    expect(stats.upkeepCostPerHour[2].amount).toBe(2.0);
+    expect(stats.upkeepCostPerHour[2].element).toBe('fire');
   });
 
   it('computes total summon cost from all components', async () => {
diff --git a/src/lib/game/data/golems/golemancy-data.test.ts b/src/lib/game/data/golems/golemancy-data.test.ts
index 3f3cf92..0b0b7f5 100644
--- a/src/lib/game/data/golems/golemancy-data.test.ts
+++ b/src/lib/game/data/golems/golemancy-data.test.ts
@@ -186,11 +186,49 @@ describe('Computed stats', () => {
     const design = makeDesign('basic', 'earth', 'simple');
     const stats = computeGolemStats(design);
 
+    // Basic core has 1 mana type (earth), so all upkeep goes to earth
     expect(stats.upkeepCostPerHour.length).toBe(1);
     expect(stats.upkeepCostPerHour[0].amount).toBe(1.0);
     expect(stats.upkeepCostPerHour[0].element).toBe('earth');
   });
 
+  it('multi-type core splits upkeep evenly across selected mana types', () => {
+    const design = makeDesign('intermediate', 'earth', 'simple');
+    design.selectedManaTypes = ['fire', 'water'];
+    const stats = computeGolemStats(design);
+
+    // Intermediate core: manaRegen=1.5, upkeep=3.0/hr split across 2 types = 1.5 each
+    expect(stats.upkeepCostPerHour.length).toBe(2);
+    expect(stats.upkeepCostPerHour[0].element).toBe('fire');
+    expect(stats.upkeepCostPerHour[0].amount).toBe(1.5);
+    expect(stats.upkeepCostPerHour[1].element).toBe('water');
+    expect(stats.upkeepCostPerHour[1].amount).toBe(1.5);
+  });
+
+  it('advanced core (3 types) splits upkeep three ways', () => {
+    const design = makeDesign('advanced', 'steel', 'simple');
+    design.selectedManaTypes = ['fire', 'water', 'earth'];
+    const stats = computeGolemStats(design);
+
+    // Advanced core: manaRegen=3.0, upkeep=6.0/hr split across 3 types = 2.0 each
+    expect(stats.upkeepCostPerHour.length).toBe(3);
+    const totalUpkeep = stats.upkeepCostPerHour.reduce((sum, c) => sum + c.amount, 0);
+    expect(totalUpkeep).toBe(6.0);
+    for (const cost of stats.upkeepCostPerHour) {
+      expect(cost.amount).toBe(2.0);
+    }
+  });
+
+  it('single-type core does not split upkeep', () => {
+    const design = makeDesign('basic', 'earth', 'simple');
+    // Basic core has manaTypes=['earth'], selectedManaTypes=[] => uses core.manaTypes
+    const stats = computeGolemStats(design);
+
+    expect(stats.upkeepCostPerHour.length).toBe(1);
+    expect(stats.upkeepCostPerHour[0].amount).toBe(1.0); // 0.5 * 2 = 1.0
+    expect(stats.upkeepCostPerHour[0].element).toBe('earth');
+  });
+
   it('selected mana types override core defaults', () => {
     const design = makeDesign('intermediate', 'earth', 'simple');
     design.selectedManaTypes = ['fire', 'water'];
diff --git a/src/lib/game/data/golems/utils.ts b/src/lib/game/data/golems/utils.ts
index 18b4310..1b978bd 100644
--- a/src/lib/game/data/golems/utils.ts
+++ b/src/lib/game/data/golems/utils.ts
@@ -81,14 +81,16 @@ export function computeGolemStats(design: GolemDesign): ComputedGolemStats {
     ...enchantments.flatMap((e) => e.summonCost),
   ];
 
-  // Player upkeep = Core.manaRegen × 2 per hour (spec §13)
-  const upkeepCostPerHour: GolemManaCost[] = [
-    {
-      type: 'element',
-      element: core.primaryManaType,
-      amount: core.manaRegen * 2,
-    },
-  ];
+  // Player upkeep = Core.manaRegen × 2 per hour, split across all mana types (spec §13)
+  const upkeepManaTypes = design.selectedManaTypes.length > 0
+    ? design.selectedManaTypes
+    : core.manaTypes;
+  const upkeepPerType = (core.manaRegen * 2) / Math.max(1, upkeepManaTypes.length);
+  const upkeepCostPerHour: GolemManaCost[] = upkeepManaTypes.map((mt) => ({
+    type: 'element' as const,
+    element: mt,
+    amount: upkeepPerType,
+  }));
 
   // Enchantment capacity = Frame.MagicAffinity(%) × Core.TierMultiplier
   // magicAffinity is stored as decimal (0.3 = 30%) per spec §5.1, so multiply by 100
diff --git a/src/lib/game/stores/golem-combat-actions.test.ts b/src/lib/game/stores/golem-combat-actions.test.ts
index e8d69cb..f8347a0 100644
--- a/src/lib/game/stores/golem-combat-actions.test.ts
+++ b/src/lib/game/stores/golem-combat-actions.test.ts
@@ -1,10 +1,11 @@
-// ─── Golem Combat Actions Regression Tests (Issue #313) ────────────────────────
-// Tests the 5 fixes applied to processGolemAttacks:
+// ─── Golem Combat Actions Regression Tests ────────────────────────────────────
+// Issue #313: Tests the 5 fixes applied to processGolemAttacks:
 // 1. Spell damage uses actual SPELLS_DEF[spellId].dmg * frame.magicAffinity
 // 2. Spell mana cost uses actual SPELLS_DEF[spellId].cost.amount
 // 3. Elemental matchup applied to basic attacks
 // 4. Enchantment effects applied to basic attacks
 // 5. Armor pierce bypasses armor fraction instead of multiplying damage
+//
 
 import { describe, it, expect } from 'vitest';
 import {
@@ -344,4 +345,3 @@ describe('processGolemAttacks - armor pierce (fix #5)', () => {
   });
 });
 
-
diff --git a/src/lib/game/stores/golem-combat-actions.ts b/src/lib/game/stores/golem-combat-actions.ts
index a6a6a11..9d1e78d 100644
--- a/src/lib/game/stores/golem-combat-actions.ts
+++ b/src/lib/game/stores/golem-combat-actions.ts
@@ -168,19 +168,40 @@ export function processGolemMaintenance(
     if (!core) continue;
 
     const upkeepPerTick = core.manaRegen * 2 * HOURS_PER_TICK;
-    const upkeepElement = core.primaryManaType;
-    const elem = upkeepElement ? newElements[upkeepElement] : null;
+    // For multi-type cores, split upkeep evenly across all mana types (spec §13)
+    const upkeepManaTypes =
+      design.selectedManaTypes.length > 0
+        ? design.selectedManaTypes
+        : core.manaTypes;
+    const splitCount = Math.max(1, upkeepManaTypes.length);
+    const upkeepPerType = upkeepPerTick / splitCount;
 
-    if (upkeepElement && elem && elem.unlocked && elem.current >= upkeepPerTick) {
-      newElements[upkeepElement] = { ...elem, current: elem.current - upkeepPerTick };
+    // Check if player can afford upkeep across all required mana types
+    let canMaintain = true;
+    for (const manaType of upkeepManaTypes) {
+      const elem = newElements[manaType];
+      if (!elem || !elem.unlocked || elem.current < upkeepPerType) {
+        canMaintain = false;
+        break;
+      }
+    }
+
+    if (canMaintain) {
+      for (const manaType of upkeepManaTypes) {
+        const elem = newElements[manaType]!;
+        newElements[manaType] = { ...elem, current: elem.current - upkeepPerType };
+      }
       maintainedGolems.push(golem);
-    } else if (!upkeepElement && newRawMana >= upkeepPerTick) {
-      newRawMana -= upkeepPerTick;
-      maintainedGolems.push(golem);
-    } else if (upkeepElement && (!elem || !elem.unlocked || elem.current < upkeepPerTick)) {
-      logMessages.push(`${design.name} dismissed — insufficient ${upkeepElement} mana for upkeep`);
     } else {
-      logMessages.push(`${design.name} dismissed — insufficient mana for upkeep`);
+      const missingTypes = upkeepManaTypes
+        .filter((t) => {
+          const elem = newElements[t];
+          return !elem || !elem.unlocked || elem.current < upkeepPerType;
+        })
+        .join(', ');
+      logMessages.push(
+        `${design.name} dismissed — insufficient mana for upkeep (${missingTypes})`,
+      );
     }
   }
 
diff --git a/src/lib/game/stores/golem-combat-maintenance.test.ts b/src/lib/game/stores/golem-combat-maintenance.test.ts
new file mode 100644
index 0000000..2521316
--- /dev/null
+++ b/src/lib/game/stores/golem-combat-maintenance.test.ts
@@ -0,0 +1,202 @@
+// ─── Golem Maintenance Upkeep Tests (Issue #315) ───────────────────────────────
+// Tests that multi-type golem cores split upkeep evenly across all mana types.
+
+import { describe, it, expect } from 'vitest';
+import {
+  CORES, FRAMES, MIND_CIRCUITS,
+} from '@/lib/game/data/golems';
+import type { GolemDesign, SerializedDesign } from '@/lib/game/data/golems/types';
+import type { RuntimeActiveGolem } from '@/lib/game/types';
+import { processGolemMaintenance } from './golem-combat-actions';
+
+// ─── Helpers ───────────────────────────────────────────────────────────────────
+
+function makeDesign(
+  coreId: string,
+  frameId: string,
+  circuitId: string,
+  enchantIds: string[] = [],
+  selectedSpells: string[] = [],
+): GolemDesign {
+  return {
+    id: `test_${coreId}_${frameId}_${circuitId}`,
+    name: `Test ${coreId} ${frameId}`,
+    core: CORES[coreId],
+    frame: FRAMES[frameId],
+    mindCircuit: MIND_CIRCUITS[circuitId],
+    enchantments: [],
+    selectedManaTypes: [],
+    selectedSpells,
+  };
+}
+
+function makeSerialized(design: GolemDesign): SerializedDesign {
+  return {
+    id: design.id,
+    name: design.name,
+    coreId: design.core.id,
+    frameId: design.frame.id,
+    mindCircuitId: design.mindCircuit.id,
+    enchantmentIds: [],
+    selectedManaTypes: design.selectedManaTypes,
+    selectedSpells: design.selectedSpells,
+  };
+}
+
+function makeActiveGolem(design: GolemDesign, currentMana?: number, attackProgress = 0): RuntimeActiveGolem {
+  return {
+    designId: design.id,
+    summonedFloor: 1,
+    attackProgress,
+    roomsRemaining: 3,
+    currentMana: currentMana ?? design.core.manaCapacity,
+    spellCastIndex: 0,
+  };
+}
+
+// ─── Tests ─────────────────────────────────────────────────────────────────────
+
+describe('processGolemMaintenance - multi-type core upkeep splitting (fix #315)', () => {
+  it('single-type core (basic) deducts upkeep from one element', () => {
+    const design = makeDesign('basic', 'earth', 'simple');
+    const serialized = makeSerialized(design);
+    const golem = makeActiveGolem(design);
+
+    const elements = {
+      earth: { current: 50, max: 100, unlocked: true },
+    };
+
+    const result = processGolemMaintenance(
+      [golem],
+      { [design.id]: serialized },
+      100,
+      elements,
+    );
+
+    expect(result.maintainedGolems.length).toBe(1);
+    // Basic core: manaRegen=0.5, upkeep=1.0/hr, HOURS_PER_TICK=0.04 => 0.04 per tick
+    const expectedDeduction = 0.5 * 2 * 0.04; // 0.04
+    expect(result.elements.earth.current).toBeCloseTo(50 - expectedDeduction);
+  });
+
+  it('multi-type core splits upkeep evenly across selected mana types', () => {
+    const design = makeDesign('intermediate', 'earth', 'simple');
+    design.selectedManaTypes = ['fire', 'water'];
+    const serialized = makeSerialized(design);
+    const golem = makeActiveGolem(design);
+
+    const elements = {
+      fire: { current: 50, max: 100, unlocked: true },
+      water: { current: 50, max: 100, unlocked: true },
+    };
+
+    const result = processGolemMaintenance(
+      [golem],
+      { [design.id]: serialized },
+      100,
+      elements,
+    );
+
+    expect(result.maintainedGolems.length).toBe(1);
+    // Intermediate core: manaRegen=1.5, upkeep=3.0/hr split across 2 types
+    // Per type: 1.5/hr * 0.04 = 0.06 per tick
+    const expectedDeduction = (1.5 * 2 * 0.04) / 2; // 0.06
+    expect(result.elements.fire.current).toBeCloseTo(50 - expectedDeduction);
+    expect(result.elements.water.current).toBeCloseTo(50 - expectedDeduction);
+  });
+
+  it('advanced core (3 types) splits upkeep three ways', () => {
+    const design = makeDesign('advanced', 'steel', 'simple');
+    design.selectedManaTypes = ['fire', 'water', 'earth'];
+    const serialized = makeSerialized(design);
+    const golem = makeActiveGolem(design);
+
+    const elements = {
+      fire: { current: 50, max: 100, unlocked: true },
+      water: { current: 50, max: 100, unlocked: true },
+      earth: { current: 50, max: 100, unlocked: true },
+    };
+
+    const result = processGolemMaintenance(
+      [golem],
+      { [design.id]: serialized },
+      100,
+      elements,
+    );
+
+    expect(result.maintainedGolems.length).toBe(1);
+    // Advanced core: manaRegen=3.0, upkeep=6.0/hr split across 3 types
+    // Per type: 2.0/hr * 0.04 = 0.08 per tick
+    const expectedDeduction = (3.0 * 2 * 0.04) / 3; // 0.08
+    expect(result.elements.fire.current).toBeCloseTo(50 - expectedDeduction);
+    expect(result.elements.water.current).toBeCloseTo(50 - expectedDeduction);
+    expect(result.elements.earth.current).toBeCloseTo(50 - expectedDeduction);
+  });
+
+  it('dismisses golem when one mana type is insufficient for split upkeep', () => {
+    const design = makeDesign('intermediate', 'earth', 'simple');
+    design.selectedManaTypes = ['fire', 'water'];
+    const serialized = makeSerialized(design);
+    const golem = makeActiveGolem(design);
+
+    const elements = {
+      fire: { current: 50, max: 100, unlocked: true },
+      water: { current: 0.001, max: 100, unlocked: true }, // Almost empty
+    };
+
+    const result = processGolemMaintenance(
+      [golem],
+      { [design.id]: serialized },
+      100,
+      elements,
+    );
+
+    expect(result.maintainedGolems.length).toBe(0);
+    expect(result.logMessages[0]).toContain('dismissed');
+    expect(result.logMessages[0]).toContain('water');
+  });
+
+  it('dismisses golem when one mana type is not unlocked', () => {
+    const design = makeDesign('intermediate', 'earth', 'simple');
+    design.selectedManaTypes = ['fire', 'water'];
+    const serialized = makeSerialized(design);
+    const golem = makeActiveGolem(design);
+
+    const elements = {
+      fire: { current: 50, max: 100, unlocked: true },
+      // water not present => not unlocked
+    };
+
+    const result = processGolemMaintenance(
+      [golem],
+      { [design.id]: serialized },
+      100,
+      elements,
+    );
+
+    expect(result.maintainedGolems.length).toBe(0);
+    expect(result.logMessages[0]).toContain('dismissed');
+  });
+
+  it('does not deduct any mana when upkeep cannot be paid (atomic check)', () => {
+    const design = makeDesign('intermediate', 'earth', 'simple');
+    design.selectedManaTypes = ['fire', 'water'];
+    const serialized = makeSerialized(design);
+    const golem = makeActiveGolem(design);
+
+    const elements = {
+      fire: { current: 50, max: 100, unlocked: true },
+      water: { current: 0.001, max: 100, unlocked: true },
+    };
+
+    const result = processGolemMaintenance(
+      [golem],
+      { [design.id]: serialized },
+      100,
+      elements,
+    );
+
+    // fire should NOT have been deducted since water couldn't pay its share
+    expect(result.elements.fire.current).toBe(50);
+  });
+});