Range Rover defective engine thermostat P0128

As a mechanic and a Range Rover owner for many years, I’ve had my fair share of experience with the infamous reliability issues of this luxury vehicle.

One common problem that causes the check engine light to come on is a defective engine thermostat.

And that, dear reader, is exactly what I’m going to talk about – Range Rover Defective Engine Thermostat P0128.

What models are affected?

• Land Rover Defender
• Range Rover Discovery
• Range Rover Evoque
• Range Rover Sport
• Range Rover Velar
• Range Rover Vogue

Signs and symptoms

How do you know if you have a defective engine thermostat on your Range Rover?

Here are the signs and symptoms to look out for:

• The check engine light comes on
• The engine temperature gauge reads lower than normal
• The engine temperature takes a long time to reach normal operating temperature
• The engine temperature fluctuates between hot and cold
• The heater doesn’t produce enough heat

If you’re experiencing any of these symptoms, it’s time to check the thermostat.

List of possible OBD codes

The OBD code associated with a defective engine thermostat on a Range Rover is P0128.

When this code appears, it means that the engine coolant temperature is below the expected range for the engine’s operating conditions for too long.

This code is often accompanied by a message stating, “Coolant temperature below thermostat regulating temperature.”

Common causes

The most common cause of a Range Rover Defective Engine Thermostat P0128 is a malfunctioning thermostat.

However, there are a few other possible causes, such as:

• A faulty temperature sensor
• A clogged or corroded cooling system
• Air pockets within the cooling system
• A damaged or leaking engine coolant hose

Can it be fixed without a mechanic?

You can fix a defective engine thermostat on your Range Rover by yourself, but if you’re not comfortable working on cars, it’s best to leave it to a mechanic.

Parts you’ll need to fix it

• A replacement thermostat
• A new gasket for the thermostat
• New engine coolant

Tools you’ll need to fix it

• A ratchet set
• A new hose clamp
• A funnel

How to fix it

Now, let’s get to the real stuff – how to fix it. Here’s a step-by-step guide to help you diagnose and fix a defective engine thermostat on your Range Rover:

1. Make sure the engine is completely cool before working on the car.
2. Locate the thermostat housing.
3. Remove the hose clamp from the thermostat housing.
4. Take out the old thermostat and gasket.
5. Put the new thermostat in place and make sure it’s seated properly.
6. Install the new gasket.
7. Reattach the hose clamp.
8. Refill the coolant reservoir with new engine coolant.
9. Run the engine and let it reach operating temperature.
10. Check for leaks and test drive the car to ensure that everything is in order.

Congratulations, you’ve done it!

Potential alternative causes

While a faulty thermostat is the most common cause of Range Rover Defective Engine Thermostat P0128, other causes may include a coolant temperature sensor that has gone bad, a failing radiator fan, or a malfunctioning engine control module.

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