What is the Heater Bypass Tube all about?

The heater bypass tube allows a small amount of coolant to circulate throughout your car engine when the thermostat is closed. It bypasses the thermostat, hence the name. Some engines are equipped with bypass hoses, while others have a bypass passage that forms a part of the cooling jacket in the engine. This is really just terminology – the effect is the same.

The bypass tube prevents excessive pressure from being built up within the system, delivers a bit of heat when the engine is started, and allows for even cooling from the point of startup. When the thermostat opens up coolant flow in your car, the engine begins to cool. The car thermostat closes a bit and increases coolant flow through the heater core and the bypass hose.

Keep in mind:

• Heater bypass tube replacement is not part of your vehicle’s routine maintenance, so your mechanic will not check it when doing an oil change or checking your fluid levels.
• Cooling problems can be devastating to your car’s engine.
• Don’t assume that the problem is the bypass tube – it could be the thermometer, the radiator, or another faulty component in the car cooling system.
• If you have pets, keep them away from leaked coolant – it is highly toxic.

How it's done:

• The vehicle's hood is opened and coolant is drained
• The two heater lines are disconnected from the heater core
• The new heater bypass tube is installed
• The coolant is refilled and the vehicle is started
• The repair is verified and the heater bypass tube tested for leaks

Our recommendation:

Problems with the heater bypass is not something you should try to diagnose or fix on your own. This is a diagnosis and repair issue that is best left to one of our expert mechanics.

What common symptoms indicate you may need to replace the Heater Bypass Tube?

• A strong smell of coolant
• A puddle of yellow-green fluid (coolant) under your car

How important is this service?

If there is a problem in your cooling system, you could end up with an overheated engine, and the repairs could be extremely expensive. Have one of our expert mechanics determine if the problem is with the bypass tube and replace it if necessary.