Pressure test the low-voltage cooling system on a 2024 Model 3 Long Range to identify leaks in the powertrain/battery coolant loops without disturbing HV components. This is a diagnostic procedure only — no coolant loop service or octovalve work is performed.

Warnings

Tools required

Parts

• Replacement coolant reservoir cap (only if existing cap fails pressure hold) × 1 — OEM Tesla coolant reservoir cap — verify by VIN

Fluids

• Tesla-spec coolant (G-48) — top-up only if level drops during test

Preparation

1. Park on level ground, place in P, engage parking brake.
2. Exit ALL doors with the key fob away from the vehicle. Wait at least 2 minutes for HV systems to fully de-energize, even on this non-HV job.
3. Disconnect the 12V low-voltage battery. On 2024 Model 3, the low-voltage battery may be a lithium unit located under the rear seat / floor area — refer to architecture notes and verify location before disconnecting.
4. DO NOT touch, cut, or pierce ANY orange cable — these are high-voltage and lethal.
5. If at any point you encounter an orange cable, an HV component, or are unsure if a system is de-energized: STOP and consult a Tesla-certified technician.
6. Allow the vehicle to sit for at least 1–2 hours after any driving or charging so the cooling system is at ambient temperature.
7. Open the frunk and locate the coolant expansion/reservoir tank. Have shop towels positioned beneath to catch any drips when the cap is removed.
8. Visually inspect the engine bay area, under-hood liner, and ground beneath the vehicle for existing coolant residue (often indicated by sticky pink/blue staining).

Procedure

1. 1

   Confirm system is cold and depressurized
   Place a hand near (not on) the coolant reservoir to confirm ambient temperature. Slowly rotate the reservoir cap one detent to release any residual pressure. Listen for hissing — if pressure releases, wait until it stops before fully removing the cap.
   ⚠️Hot pressurized coolant can spray and cause severe burns. If any pressure is felt, stop and let the system cool further.
2. 2

   Check baseline coolant level
   With the cap off, verify coolant level is between MIN and MAX on the reservoir. Note the level. If low, this alone may indicate a leak. Do not top up before testing — running the test slightly low is fine and helps you observe level change.
3. 3

   Remove the reservoir cap and inspect
   Fully remove the reservoir cap. Inspect the cap's rubber seal for cracking, swelling, or coolant crust. A failed cap is a common cause of pressure loss and is itself a valid test target later. Inspect the reservoir neck for damage or contamination.
4. 4

   Install the pressure tester adapter
   Select an adapter from the pressure test kit that matches the reservoir neck threads/profile. Thread or seat the adapter hand-tight — do not overtighten or use tools, as the plastic reservoir neck can crack. Confirm a sealed fit.
5. 5

   Connect the pressure pump
   Connect the hand pump to the adapter. Verify the gauge reads zero before pumping. Identify the system's rated pressure from the OEM cap marking (typically printed on the cap itself). Do not exceed that value.
6. 6

   Pressurize the system
   Slowly pump the system up to the cap's rated pressure (do not exceed). Pump in steady strokes and watch the gauge — if pressure will not build at all, there is a large leak; stop pumping and begin visual inspection immediately.
   ⚠Never exceed the cap's rated pressure. The Model 3 cooling system shares plumbing with the battery cold plate and heat pump — over-pressure can damage seals that are not field-serviceable.
7. 7

   Hold and observe pressure for 15 minutes
   Watch the gauge. A healthy system should hold pressure with minimal drop (a small drop as air bleeds is normal in the first 1–2 minutes, then stabilize). A continuous steady drop indicates a leak. Note the rate of pressure loss.
8. 8

   Locate leaks visually (top-side)
   While pressure is held, inspect the frunk area: reservoir body, reservoir-to-hose connections, visible coolant lines, radiator inlet/outlet, and the visible portion of the front cooling module. Look for active drips, fresh wet spots, or bubbling. Use an inspection mirror for hidden runs.
9. 9

   Inspect underbody (without removing aero shields if avoidable)
   Look under the vehicle along the front subframe and where coolant lines route toward the rear. If a leak is suspected but not visible, the front aero/belly panel may need partial removal (separate procedure) for access. Do NOT pull panels covering the HV battery or octovalve area.
   ⚠️Stop if any inspection requires touching, moving aside, or disturbing orange HV cabling or the octovalve assembly. These are dealer-only zones.
10. 10

    Test the cap separately
    If the system holds pressure, separately pressure-test the reservoir cap using the cap adapter in the test kit. The cap should hold its rated pressure without bleeding off. A failed cap is a common and inexpensive cause of coolant loss on these vehicles.
11. 11

    Release pressure and remove tester
    Use the pressure relief valve on the pump to slowly bleed system pressure to zero. Confirm the gauge reads zero before disconnecting. Remove the adapter from the reservoir neck by hand.
12. 12

    Document findings
    Record: starting pressure, pressure after 15 minutes, observed leak locations (if any), and cap condition. If a leak is at the octovalve, heat pump, or battery cold plate interface — flag for dealer service and do not attempt field repair.

Reassembly

1. If coolant level dropped during the test, top up with Tesla-spec coolant (G-48) to the MAX line. Do not mix with non-G-48 coolants.
2. Reinstall the reservoir cap. Tighten hand-tight to the cap's detent stop — do not use tools.
3. Wipe down any spilled coolant from the reservoir, hoses, and surrounding plastics (coolant residue attracts dirt and can mimic future leaks).
4. Reconnect the 12V low-voltage battery negative terminal.
5. Close the frunk.

Verification

• Power the vehicle on and check the touchscreen for any cooling, thermal, or battery temperature alerts. None should be present.
• Allow the vehicle to idle/sit awake for 5–10 minutes so the thermal system cycles pumps. Listen for normal coolant pump operation (faint whirring) and check the reservoir level remains stable.
• Drive the vehicle for a short distance (or initiate a Supercharge preconditioning event) to bring the system up to operating temperature, then re-check reservoir level and inspect for fresh leaks once cooled.
• Note: Tesla recommends battery coolant inspection at 4 years / 50,000 mi. Log the test date and pressure-hold result so the next inspection is informed.

More procedures for this vehicle