Symptoms of a Bad or Failing Heater Bypass Tube

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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.

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.

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.


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Fabrice

18 years of experience
133 reviews
Fabrice
18 years of experience
Toyota Yaris - Brake Pads Replacement (Front) - Orlando, Florida
My appointment was late in the day, so being late was expected. Fabrice notified me ahead of time about his tardiness. When he arrived, he was apologetic, courteous and professional. He got to work right away and let me know of other work that was needed for future appointments

Oreste

12 years of experience
111 reviews
Oreste
12 years of experience
Nissan Frontier - Brake Pads Replacement (Front) - Miami, Florida
The best ever!!!! Will not use anyone else in future .. very knowledgeable and explained every thing to me .very professional, well spoken .

Breck

18 years of experience
527 reviews
Breck
18 years of experience
Jeep Patriot - Brake Pads Replacement (Front, Rear) - Houston, Texas
Becks was very informative about things that I didn't know needed to be looked at with my car. He fixed little hick ups quickly and had me ready to get back on the road sooner than I thought he would.

Miguel

19 years of experience
63 reviews
Miguel
19 years of experience
Audi allroad - Brake Pads Replacement (Front) - Fair Lawn, New Jersey
Miguel is very professional mechanic. He called me in advance about his coming. He brought the quality parts (brakes pads and rotors) and done his job quickly and of great quality. I tested the brakes after the replacement and they were efficient and very silent. I would recommend him very much.

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