Skip the auto shop - Our mechanics make house calls

Symptoms of a Bad or Failing Heater Bypass Tube

heater bypass tube

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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
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

Post a question and get free advice from our certified mechanics.

ASK A QUESTION

More related articles

Insurance Requirements for Car Registration in Kentucky
The Kentucky Transportation Cabinet requires that all drivers in Kentucky carry liability automotive insurance, or “financial responsibility” in order to operate a vehicle legally and maintain vehicle...
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...
Veteran and Military Driver Laws and Benefits in New Mexico
The state of New Mexico offers a number of benefits and perks for those Americans who have either served in an Armed Forces branch...


Related questions

Q: No heat after adding coolant and thermostat almost to H

Hello. If the coolant was that low then that will cause the heater to not work. The most important thing at this time would be to determine where the coolant went. For it to be this low that means it...

Q: Gross smell from the AC

It sounds to me like the drain for the A/C system is clogged. When you run the vehicle’s air conditioner, condensation forms on the evaporator, just as it forms on a glass of ice water. The A/C drain allows the...

Q: Car turns off after driving 20 miles

Hello there, a few different parts can cause the vehicle to stall out and die like you have described. The most likely are the fuel pumps, an intermittent wiring issue, a bad battery cable, a faulty EGR, vacuum leak or...