Mechanic Wiki: How to Bleed Coolant on a Kia Ray EV: Step-by-Step Guide

Learn how to properly bleed the coolant system on your Kia Ray EV. Step-by-step instructions, safety tips, and troubleshooting for DIY owners.

Published: June 29, 2026
Last Updated: June 29, 2026

Quick Answer

To bleed the coolant system on a Kia Ray EV, you typically activate the electric water pump by turning the ignition ON (without starting the traction motor) while the HVAC is set to full heat and high fan. Open the bleed screw on the coolant return line near the motor/inverter unit until a steady stream of coolant flows without bubbles, then close the screw. If the pump doesn’t run automatically, you may need a diagnostic scan tool to enter “Coolant Pump Activation” mode. Total time: 15–30 minutes. Always use approved EV coolant and follow high-voltage safety rules.

Why Coolant Bleeding Is Critical for Your Kia Ray EV

The Kia Ray EV uses a combined cooling loop that manages temperatures for the traction motor, inverter, onboard charger, and the high-voltage battery pack. Unlike a conventional internal combustion engine, an EV’s thermal system is sensitive to even small air pockets. If air becomes trapped:

Battery temperature rises faster, potentially triggering power reduction or charging slowdown.
Inverter efficiency drops, which can reduce driving range by 5–10% in extreme cases.
Cabin heater performance suffers, since the heat pump or resistive heater relies on coolant flow.

You should bleed the system after any of these events:

Draining and refilling coolant
Replacing a hose, water pump, or thermostat
Overheating incidents where the coolant low warning appeared
Noticing air bubbles in the clear return line

Neglecting to bleed properly can cause repeated error codes related to the Battery Management System (BMS) or motor temperature sensor — an issue many DIY owners encounter.

Safety Precautions Before Starting

Working on an EV cooling system requires extra caution because the coolant lines can run near high-voltage components. Follow these rules:

High-voltage awareness: Never touch orange-colored cables or open sealed cooling lines without verifying zero voltage. The system’s capacitors can hold charge for up to 10 minutes after power-off — wait that time before touching any metal fittings near the inverter or battery pack.
Wear insulated gloves and safety glasses: Coolant can be hot (even after sitting) and may contain conductive additives.
Use only approved EV coolant: The Kia Ray EV requires a blue or pink ethylene-glycol based coolant specifically for electric vehicles (often labeled “EV Coolant”). Mixing with universal green coolant can cause gel formation and damage the water pump.
Work on a level surface with the ignition OFF and the key removed from the vehicle.
Keep a fire extinguisher rated for electrical fires nearby as a worst-case precaution.

Tools and Materials Needed

Item	Notes
Kia Ray EV service manual (or reliable database)	Required for exact bleed screw location and pump activation sequence
Approved EV coolant (e.g., Kia Long-Life Coolant for EVs)	Check owner’s manual for color/type
Distilled water (if mixing pre-diluted coolant)	Only if coolant requires 50/50 mix
Funnel with long spout	Helps avoid spills into electrical connectors
Clean rags or shop towels	Expect some drips at bleed screw
Bleed screw tool (usually 10mm socket or Phillips head)	Check your model year
Diagnostic scan tool (optional but recommended)	Needed if pump does not activate manually
Container for old coolant	Dispose of properly
Multimeter (to verify no high voltage present)	For peace of mind when working near HV components

Step-by-Step Coolant Bleed Procedure

1. Preliminary Checks

Fill the reservoir to the “MAX” line using the correct coolant. Do not overfill.
Inspect all hoses — look for cracks, loose clamps, or signs of previous leakage. Tighten any loose clamps.
Charge the 12V battery: A low 12V battery can prevent the electric water pump from running. If the vehicle has been sitting, connect a trickle charger to ensure adequate voltage.

2. Locate the Bleed Valve

On most Kia Ray EV models, the bleed screw sits on top of the water outlet pipe near the motor/inverter unit. This is often behind the access panel on the driver side, just behind the front bumper. Check your specific model year diagram — some variants have a second bleed screw on the battery cooling loop.

The bleed screw is usually a plastic or brass fitting with a small hex head (10mm or Phillips). Do not confuse it with a mounting bolt.

3. Open the Bleed Valve

Loosen the bleed screw about half a turn — do not remove it completely. You should see a slight weep of coolant.
Place a rag underneath to catch drips.
If the screw is stuck, apply light penetrating oil and wait 5 minutes. Do not force it — the housing is plastic on some models and can crack.

4. Activate the Electric Coolant Pump

This step can vary by model year, but here are the two most common methods:

Method A — Manual activation (most models)

Insert the key and turn the ignition to ON (or press the start button without your foot on the brake pedal to enter “ACC” or “Ready” mode — consult manual).
Turn the HVAC system to the hottest temperature setting and set the fan to maximum speed.
The electric coolant pump should start running within 10–20 seconds. You will hear a whirring sound from the front of the vehicle.
Let the pump run for 2–3 minutes while you watch the bleed valve.

Method B — Diagnostic scan tool activation

If the pump does not run after 30 seconds with HVAC on max, you need a scan tool.
Connect a compatible OBD-II scanner (e.g., Launch X431, Autel, or a Kia-specific tool) and enter the BMS (Battery Management System) section.
Look for “Coolant Pump Activation,” “Bleed Mode,” or “Air Purge” command.
Run the pump for 3–5 minutes.

What to observe: Coolant should flow steadily from the bleed screw — first with small air bubbles, then a continuous stream without bubbles. If no flow appears, check that the pump is actually running (you can feel vibration on the coolant hose near the reservoir).

5. Close the Bleed Valve

Once you see a steady, bubble-free stream of coolant, tighten the bleed screw to roughly 2–3 Nm (hand-tight plus an eighth turn). Do not overtighten — the plastic threads strip easily.
Wipe any spilled coolant immediately with a clean rag.

6. Check and Refill Reservoir

After the pump cycle ends (or after you stop it with the scan tool), check the coolant reservoir level. It will likely have dropped slightly.
Top off to the MAX line.
If the level drops significantly within 5 minutes, there is still air in the system. Repeat the activation cycle (step 4) and watch for additional bubbles at the bleed screw.

7. Verify System Integrity

Leak check: Inspect around the bleed screw, all hose clamps, and the water pump area for drips. Run the pump one more short cycle (30 seconds) while looking.
Final level check: Turn off ignition. Wait 10 minutes, then recheck the reservoir. The level should remain at or near MAX. If it has dropped, repeat the process.

Troubleshooting Common Issues During the Bleed

Air Pocket Remains After Procedure

Cause: The pump cycle was too short, or the bleed valve is not at the system’s highest point.
Solution: Repeat the pump activation for a full 5-minute cycle. While the pump runs, gently tap the coolant hoses with a rubber mallet or wooden handle to dislodge trapped air. Park the vehicle nose-up on a slight incline if possible — this helps air travel toward the bleed screw.

Coolant Pump Does Not Run When Ignition Is ON

Check the 12V battery — if voltage is below 12.2V, the BMS may inhibit pump operation. Charge the battery and retry.
HV isolation faults — use a scan tool to check for high-voltage trouble codes. If the system detects a short or loss of isolation, it will disable the coolant pump. You may need professional diagnostics.
Early model quirk: Some 2013–2015 Kia Ray EVs require you to briefly start the traction motor (press brake + start) and then immediately turn it off to trigger the pump cycle. The motor runs for only 2 seconds, but the pump continues for several minutes. Try this if the usual method fails.

Coolant Level Drops After Test Drive

Normal: Small air pockets in the heater core or battery cooling plates can take a few drive cycles to fully purge. Top off the reservoir again after a short drive (5–10 km). If the level continues dropping after a second top-up, inspect for an external leak at the water pump weep hole or hose connections.

Maintenance Tips for Kia Ray EV Coolant System

Change interval: Every 60,000 km or 4 years, whichever comes first. The coolant degrades over time and loses corrosion inhibitors needed to protect the aluminum components in the inverter and battery.
Coolant type: Many Kia Ray EVs require “Kia Coolant for Electric Vehicles” (blue). Do not use universal green coolant — it contains silicates that can clog the water pump seal and reduce thermal conductivity.
Cap seal: If you frequently see low coolant with no visible leaks, check the reservoir cap. The pressure rating is typically 16–20 psi. A worn seal lets coolant evaporate slowly. Replace the cap if the rubber seems hard or cracked.
Hose inspection: EV cooling systems operate at lower temperatures than ICE cars (typically 45–55°C for the battery loop), but hoses still degrade. Replace any hose that feels soft, bulging, or brittle.

Frequently Asked Questions

Q1: Can I bleed the coolant system without a scan tool?
A: Yes, on many Kia Ray EVs you can activate the pump by turning the ignition ON with HVAC set to max heat and high fan. If that doesn’t work, a scan tool is necessary — some model years require a BMS command to run the pump in air purge mode.

Q2: What type of coolant does the Kia Ray EV use?
A: It uses a blue or pink ethylene-glycol based coolant specifically formulated for electric vehicles (often listed as “EV Coolant”). Never mix with traditional green coolant. Refer to your owner’s manual — most specify “Kia Coolant for Electric Vehicles” or equivalent.

Q3: How do I know if there is still air in the system after bleeding?
A: Symptoms include intermittent low coolant warning, heater not working properly, or the battery temperature rising faster than normal. Use an OBD-II scanner to check coolant temperature sensor readings — erratic fluctuations (sudden jumps of 10°C or more) indicate trapped air.

Q4: Is the coolant bleed procedure the same for the battery pack and the motor/inverter?
A: No. This guide covers the combined HVAC/motor/battery cooling circuit found on most Kia Ray EVs. Some early models or cold-climate versions have a separate battery heater loop with its own bleed screw. Always consult the service manual for your exact model year.

Q5: What should I do if coolant leaks from the bleed screw after tightening?
A: Replace the bleed screw O-ring (often a standard 8mm rubber seal) or apply PTFE tape sparingly to the threads. Do not overtighten — the plastic housing can crack. If the screw itself is damaged, order a replacement from a Kia dealer.

Q6: Do I need to disconnect the high-voltage battery before bleeding?
A: No, you do not need to disconnect the HV battery unless you are servicing the cooling components directly. The pump runs on 12V power. However, avoid touching any orange cables and follow standard EV safety rules as described in the safety section above.

About the Author: Erwin Salarda is an Automotive Service Equipment Technician based in the Philippines, specializing in computerized automotive diagnostic equipment such as OBD scanners and wheel alignment systems. Since 2012, he has been actively providing technical support, equipment installation, troubleshooting, after-sales service, and hands-on training for automotive service equipment used by workshops and automotive professionals.

He has received specialized training from international suppliers and manufacturers, including Launch X431 in Shenzhen, China, Lawrence Engineering Company in Guangzhou, China, and 3Excel Wheel Alignment Company in Shenzhen, China. Through these trainings, he developed advanced expertise in automotive diagnostics, calibration, wheel alignment systems, and computerized automotive service technologies.

Erwin Salarda provides professional after-sales support and technical training for automotive diagnostic and wheel alignment equipment, helping clients maximize the performance and proper use of their tools and systems. His experience covers equipment setup, software updates, calibration procedures, troubleshooting, and operational guidance for automotive workshops and service centers.

With more than a decade of experience in the automotive equipment industry, Erwin Salarda continues to support automotive businesses by delivering reliable technical expertise and practical training solutions.

For inquiries and equipment purchases, please visit https://carlifterph.com/