Car Heater Hose Replacement: A How-To Guide

Open your hood and let everything cool down

Don’t touch anything until you can do so comfortably — you’ll risk serious burns if you don’t. You might need to wait up to 45 minutes, but better to be safe than sorry.

As the engine cools, look for splits or tears in the hoses. The telltale signs of a blown hose will be coolant splashed over the engine and under the hood. This alone doesn’t mean you have a blown hose, however. It could be a faulty thermostat that caused the radiator cap to release.

If the cap has a pressure-release flap that’s released, your engine may have only overheated. But if the cap is intact and you can see a leak in the heater hose, you can fix it. Once the engine cools, remove the radiator cap. Put the cap back on after the fix.

Look for a leak along the length of your heater hose

Carefully examine the hose from the water pump back to the heater core inlet and outlet near the firewall (i.e. the backside of the engine compartment).

“A thorough check for leaks requires attention to white crusty deposits along the hose that indicate dried coolant from a slow leak,” says Alan Gelfand, owner of German Car Depot. Also, sometimes rubber hoses tend to develop leaks at their metal-fitting connection points. “This is common in vehicles such as BMWs and Mercedes, but it tends to happen on other vehicles as well, so that is something else to look out for when inspecting for a coolant leak,” he says.

Cut out the bad section of hose

The leak may be at a fitting on the water pump or even at the heater core. If this is the case, you won’t need to use the coupling. Just cut the bad end off the hose, stretch the hose and reclamp it to the fitting. If the leak is along the hose, cut it at the leak and remove the bad section.

Push the hose firmly onto the coupling

Apply coolant to the coupling as a lubricant. Insert one end and tighten the clamp on it. Then slip the second clamp over the hose and push the other end of the coupling into the hose.

Ideally, it’s also a good idea to keep some silicone lubricant in the car for just such an emergency, says Gelfand. “But apply it sparingly, or it can potentially cause more bad than good with the mess it’ll make,” he says.

Check the hose coupling

Hose couplings come in several sizes, so make sure to buy the correct size. You can visually determine the right size or look up the specs in your owner’s manual.

Tighten the clamps

Before adding the clamps, inspect the hose and fittings for signs of damage. Both should be clean, smooth and without rust. Then slip the hose onto the coupling and tighten both clamps. Don’t cowboy the hoses; they may be fragile and need replacement.

Most people make the mistake of not placing the hose correctly onto the fitting before applying the clamp,” says Gelfand. The hose must extend 3/4” beyond the fitting for establishing a fail-proof connection. Then, place the clamps 1/4” the end of the fitting.

Depending on what kind of coolant your vehicle takes, you may be able to add water to your reservoir or radiator. But beware, because mixing water with some coolants can cause even more damage to your car. If your specs warn against adding water, drive (no longer than 10 minutes!) to the nearest place you can get coolant.

This fix isn’t permanent, so make an appointment to have your hoses and coolant checked and replaced. And, if your car is more than six years old, no doubt your radiator and heater hoses have seen better days. Next time you’re in the auto supply store, pick up a kit containing a heater hose coupling and a pair of clamps. The kit doesn’t cost much and it’s a good insurance policy.

In the future, be on the lookout for telltale signs that your hose might have a problem, such as a sweet smell coming through the vents of your car (that’s coolant) or a puddle of coolant on the passenger side floor, which has leaked through the dashboard.

“If you notice these signs or otherwise sense there may be something going on, visually inspect your heater hoses for swelling, cracks and leaks,” says Duane “Doc” Watson of Bosch Mobility Aftermarket. “A hose in good condition should feel firm and be able to retain its shape after a squeeze. If your hose has cracks, is too hard to squeeze or is too soft, it should be replaced.”

FAQs

What happens if I don’t replace a damaged heater hose?

You could break down on the road, which could cause costly damage to your vehicle. The first symptoms of a coolant leak are your heater and windshield defroster not working well. But the main danger comes from overheating your engine to the point that it will need to be replaced. In the meantime, the leak will also shorten the lifespan of other components, including your water pump and sensors.

“Remember that connectors for sensors and solenoids are typically all made of plastic, and the increased temperatures will cause this plastic to degrade more rapidly and become brittle more quickly,” says Gelfand.

Do I need to replace both heater hoses at the same time?

No, but if one failed because of deterioration, it’s a good idea to also replace the other, as it might also be compromised by age and wear. However, “If there are other external factors at play, like maybe one hose was cut or burned, for instance, the other one is probably safe to keep, as long as it passes a visual inspection,” says Watson.

About the Experts

• Chris “Moose” Pyle is a master-certified technician with 20-plus years of automotive experience, and an auto expert on JustAnswer, the expert on-demand platform.
• Duane “Doc” Watson is a technical trainer at Bosch Mobility Aftermarket. He has more than 45 years of experience in automotive repair, has trained thousands of technicians and earned many industry awards, including Chevrolet Technician of the Year and Buick Service Master of the Year.
• Alan Gelfand has been the owner of German Car Depot for more than 30 years. His business is an independent automotive service center in Hollywood, Florida, specializing in the service and repair of German vehicles.