Skip the auto shop - Our mechanics make house calls

Symptoms of a Bad or Failing Heater Bypass Tube

heater bypass tube

Bad or Failing Heater Bypass Tube Inspection

by a top-rated mechanic at your home or office

The heater bypass tube is a cooling system component found on many road going cars and trucks. It’s purpose is to serve as a cooling system passage that bypasses the thermostat, so that there is coolant flow even when the engine thermostat is closed. The coolant bypass tube provides a passage for minimum coolant flow, so that the engine does not overheat from insufficient cooling when the thermostat is closed and restricting coolant flow.

While servicing the bypass tube is not generally considered routine maintenance, it is still prone to the same issues that all cooling system components are susceptible to, and can sometimes require attention. Usually a faulty heater bypass tube will produce a few symptoms that can alert the driver of an issue.

HAVE SYMPTOMS OF CAR TROUBLE?
Get an $80 diagnostic
by a top-rated mechanic at your home or office.

Get a quote · Book an Appointment · Our expert mechanics come to you.

Coolant smell

One symptom of an issue with heater bypass tube is a coolant smell from the engine bay. Most heater bypass tubes use an o-ring or gasket to seal the bypass tube to the engine. If the o-ring or gasket wear out or tear, coolant will begin to leak from the bypass tube. This may produce a coolant smell from the vehicle’s engine bay. Some coolant bypass tubes are located near the top of the engine, and as a result may produce a coolant smell far before any coolant can be visibly detected without opening the hood.

HAVE SYMPTOMS OF CAR TROUBLE?
Get your car fixed at your home or office.

Get a quote · Book an Appointment · Our expert mechanics come to you.

Coolant leak

The most common symptom of an issue with the heater bypass tube is a coolant leak. If the bypass tube gasket or o-ring become damaged, or the bypass tube leaks due to excessive corrosion it may cause a coolant leak. Depending on the severity of the leak, coolant may or not leak onto the floor or underneath the vehicle. A faulty gasket or o-ring may require a simple replacement of the seal, while a corroded tube will usually require replacement.

As the coolant bypass tube is a component of the engine’s cooling system, it’s failure can lead to engine overheating and potential serious engine damage. If your vehicle’s bypass tube is leaking, or has another issue, have the vehicle inspected by a professional technician, such as one from YourMechanic, to determine if the bypass tube requires replacement.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Still not sure about your car's issue?
Diagnose your car
What kind of issue are you experiencing?
Brakes are squeaking
Car is not starting
Car is overheating
Car is shaking (vibrating)
Fluids are leaking
Heating and A/C
Smoke or steam is coming out of the car
Warning light is on
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

How to Transfer a Car Title in Idaho
In order to prove ownership of a car, you must have the title. However, when a car is sold, given away or inherited, the title needs...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
P2159 OBD-II Trouble Code: Vehicle Speed Sensor B Range/Performance
Diagnostic Trouble Code (DTC): P2159 P2159 code definition Vehicle Speed Sensor B Range/Performance...


Related questions

Q: Heat in the front won't work

Hi there. The front heater core my be restricted. A cooling system flush may resolve the problem. It may be a faulty temperature blend door actuator if the blower motor is still not operational. Checking the fuse would be in...

Q: HVAC controls don't work. All fuses are good and the relay works. there is still no power to HVAC unit.

Hi there. Check to see if there is power to the air conditioning controls. If there is power to the controls and there is power to the fuse and relay, then the air conditioning controls need replaced. If there is...

Q: Are Cracked Hoses Repairable, or Should They Be Replaced?

Cracked hoses are unsafe for the proper operation of your vehicle and should be replaced at your earliest convenience. There is no way to repair a worn hose, nor would you want to. Hoses are designed to transfer engine coolant...