The radiator hoses on your vehicle typically connect the radiator inlet and outlet to the water outlet or thermostat housing and the water pump on the engine. As the engine runs and turns the water pump, it pressurizes the cooling system to ensure that coolant circulates throughout the engine. When the engine reaches operating temperature and the thermostat opens, hot coolant travels through the upper radiator hose to the inlet on the radiator to be cooled. Once the coolant has passed through the radiator and the temperature has been reduced, it is pumped back into the engine by the water pump. The water pump is often connected to the radiator outlet by a lower radiator hose, but on some vehicles, a water inlet may work as an intermediary between the pump and the hose.
The cooling system on your vehicle is made up of a few major parts, including the radiator, water pump, recovery tank, and perhaps most importantly, hoses. Hoses connect the various parts of your cooling system to one another to keep coolant flowing freely through the system and prevent leaks under pressure. Radiator hoses, heater hoses, bypass hoses, and more form the connections necessary to prevent overheating and ensure proper heat dissipation, and are even involved in keeping your interior warm in the winter months. Cooling system hoses are designed to stand up to high temperatures and pressures, but like all rubber components, hoses are susceptible to wear and failure over time. Regularly inspecting the hoses on your vehicle can help you determine when they start to fail, and allow you to address the problem before your engine overheats or you end up stranded waiting for a tow truck.
Types of Cooling System Hoses
Though all of the hoses in the cooling system serve a relatively simple purpose, they may be designed differently based on their specific purpose in the system. Each type of hose may also use a different type of connection style, depending on what parts they are connecting, so it’s important to know the specifics of your vehicle before diagnosing or replacing any hose.
Radiator Hoses
Heater Hoses
Heater hoses carry hot coolant to and from the heater core in the cabin of your vehicle. Heater cores work similarly to radiators and allow heat to radiate from the coolant, reducing its temperature. This hot air is moved by the blower motor through the vents and into your cabin. Once coolant has passed through the heater core, it is returned to the engine via another heater hose. The heater hoses may be connected to the water pump, the intake, or another separate water inlet and outlet near the thermostat to ensure that the warmest coolant reaches the heater core.
Coolant Recovery/Overflow Hoses
As coolant in the system warms up, it can expand and increase in volume or even evaporate. Because cooling systems are designed to work with a specific amount of liquid in the system, it is necessary to allow coolant vapor and excess liquid volume to vent to the coolant recovery tank or coolant reservoir. These reservoirs are designed to capture the coolant and return it to the system once it has cooled down. The coolant recovery tank may be connected to the radiator, water pump, or other locations on the engine using several coolant overflow hoses. There are usually two to three hoses that operate this system, and at a minimum, there will be a send and return overflow hose connected to the radiator or engine and the tank. The radiator cap or other pressure-sensitive valve is also very important to this system, as it helps to control the flow of coolant and prevents excess cooling system pressures that could cause hose or component damage.
Bypass Hoses
The bypass hose is typically a short molded hose that connects the water pump to the intake manifold or thermostat housing. Bypass hoses are designed to keep coolant flowing throughout the engine until the thermostat opens and releases hot coolant to the radiator. This helps ensure that no hot spots or isolated overheating occurs while the thermostat is in the closed position while also reducing pressure buildup in the engine.
Oil Cooler/Transmission Cooler Hoses and Lines
Though these components may not be part of the traditional cooling system, they are still necessary to prevent these fluids from overheating. Transmission cooling lines and hoses typically transport transmission fluid to and from the radiator or a dedicated transmission cooler mounted in front of the radiator. Oil cooler lines may transport oil to a dedicated oil cooler in front of the radiator, or in some cases, may use coolant that is circulated between an oil filter cooling mount and the radiator to keep the oil at an appropriate temperature for safe engine operation.
Symptoms of Bad Cooling System Hoses
There are a few symptoms that you may experience in your vehicle if one or more of your cooling system hoses has begun to fail. If you experience any of these problems, it’s a safe bet that you have some kind of a cooling system problem, and inspecting your hoses for signs of damage is usually a great place to start your diagnosis.
Coolant Leaks and Low Coolant Levels
This may seem obvious, but if your coolant hoses are damaged, you are likely to experience a coolant leak. You can learn more about how to identify automotive fluids with this helpful resource. If you’ve noticed coolant on the ground near your vehicle, or if your coolant recovery tank is unexpectedly empty or the coolant level in the tank is lower than usual, it may be a good idea to refill the cooling system and start looking to see where the leak may be originating. Of course, hoses aren’t the only part of the cooling system that can leak, so it may be necessary to perform a thorough check to attempt to isolate the source of the leak.
Overheating
Even if you haven’t noticed leaks, low coolant levels can quickly lead to engine overheating. Though your system can operate with a small amount of coolant and cool somewhat effectively, if there is not enough coolant to circulate, you’re likely to see your temperature gauge rise or warning light turn on. Driving for any period of time while your engine is overheating can lead to engine damage, including a blown head gasket, cracked or warped cylinder head, engine block damage, and more. It’s usually best to park your vehicle until you can determine the source of the problem, or get it to a shop as soon as possible. Other possible causes of engine overheating could include a damaged water pump or radiator, a stuck thermostat, or other obstructions caused by contamination in the cooling system, so be sure to be thorough in your diagnosis.
Steam from Under the Hood
When coolant leaks from your cooling system, depending on where it is leaking, it can land on hot parts of the engine. This may include the exhaust pipes, exhaust manifolds, or even the radiator itself in some cases. When coolant comes in contact with hot engine parts, it can evaporate and turn to a white smoke or steam. In some cases this may be severe enough to see it while driving, but often this is most easily noticed when at idle. In any case, if you have steam coming from under your hood, it’s a good idea to pull over and check to see where it might be coming from before your engine overheats.
Poor Heater Performance
This is likely the least concerning issue on this list, but a lack of coolant circulation can also affect your interior heater. If your heater hoses are obstructed or damaged, coolant may be leaking or not reaching the heater core, and when this happens, your vehicle’s heater may not get as warm as it should. This issue could also be caused by an obstructed heater core, a thermostat that is stuck open, or a heater control valve that is stuck closed, but checking the hoses for signs of damage or blockages is often a good place to start.
How to Inspect Cooling System Hoses
Making hose inspection part of your car’s routine scheduled maintenance can help alert you to problems before they become roadside emergencies, and physically inspecting the hoses only takes a couple of minutes in most cases. There are three factors to look for when inspecting the hoses on your vehicle.
1. Cracks, Tears, or Abrasions
Inspecting your radiator hoses for signs of physical damage can usually be done with the naked eye, though if you suspect a problem, an inspection mirror may come in handy. Any signs of tearing or cracking, pinholes, or areas where the hose has rubbed on another part and suffered damage are a good enough reason to justify replacing the hose. Because the cooling system operates under pressure, it’s only a matter of time before these problems get worse and the hose bursts, leading to a much more inconvenient repair and the risk of overheating.
2. Signs of Leaks
Even if the hose doesn’t appear to be physically damaged, a coolant leak near a hose outlet could be due to a hose that has deteriorated past its useful life. Leaks could also be related to the part the hose is connected to, so a more thorough inspection of the connection and the hose is recommended before simply replacing the hose. Dryness or cracking on the surface of the hose around the hose clamp, or a clamp that is loose or no longer tightening properly are also factors that could cause coolant to leak from the ends of your hoses.
3. Spongy or Hard Coolant Hoses
This test requires you to be a little more hands-on, but is a good idea to include in your maintenance routine if you don’t see any physical damage or leaks. It’s usually best to let the vehicle cool before performing this test to reduce the risk of burning yourself, and make sure to put on work gloves before touching any part of a warm cooling system. With one hand, grasp the hose and squeeze. The rubber should be flexible with a little bit of pressure, but should not be too soft or noticeably spongy. If the hose seems to give too much, or if it is brittle and can’t be squeezed without rot or cracks being exposed, it is time for the hose to be replaced. Though it may be working and show no signs of damage or leaks, it’s only a matter of time before an overly-soft or hard hose bursts or develops leaks.
How to Replace a Cooling System Hose
Though this is a relatively straightforward repair on most vehicles, every vehicle is different and the cooling system hoses may not always be designed exactly the same way. For even more information, check out our video on how to replace upper and lower radiator hoses. If you're not comfortable performing this repair, we can also recommend a local shop to help you replace cooling system hoses. The most important step in performing any cooling system repair is to drain the coolant. This is often done using a drain cock located in the radiator. Be sure that your vehicle is cooled down completely to prevent injury, then you can open the system at the radiator cap or coolant recovery tank cap. You will need a drain pan, but in most cases, radiator drain valves are designed to be loosened by hand. Once your drain pan is in place, unscrew the drain valve and let the coolant drain from the system.
Once this is done, you will need to determine how the hose is attached. Most cooling system hoses are held in place with a hose clamp, and hose clamps can come in a variety of designs. Many OE-installed hose clamps are spring band-style clamps which rely on integral tension to maintain a seal at the hose end. These clamps can usually be compressed with pliers and expanded until their diameter is large enough for the clamp to be removed. Worm drive or spiral-style hose clamps use a threaded bolt that grabs the band, and are usually installed and removed using a Phillips or flat screwdriver or a socket and ratchet. These types of clamps may be OE or can be added as an aftermarket option, and allow the user to control the tension applied to the clamp. Some of these hose clamps even feature a thumbscrew to allow for tightening and loosening by hand. Finally, some cooling system hoses, especially heater hoses, may feature quick-connect fittings that include a locking tab or other proprietary connector type. In some cases these can be removed using basic tools you may have at your disposal, or they may require a specific quick-disconnect tool to remove them.
Once the hose clamps or connectors have been removed, in most cases you can simply grasp the hose and use a twisting motion while pulling outward to remove it from the connector. Corrosion may have formed between the hose inlet or outlet and the hose itself, and a pick or hose removal tool can help you break the bond between the two surfaces. In extreme cases, especially when you are not planning to reuse the hose, they can also be cut using a utility knife. This can allow you to release the bond between the hose and port more easily so that it can be removed.
It is usually a good idea to also look at the inlet and outlet ports with the hose removed to ensure that they are not heavily corroded or damaged, as this may prevent the new hose from sealing properly. You should also inspect the condition of your hose clamps and determine if they can be reused. Once you’re satisfied with the condition of your ports and clamps, the hose can simply be reinstalled on the ports and the hose clamps tightened. Keep in mind, your hose will be connected at both ends, so it may be a good idea to slide the hose clamps onto the body of the hose before it is installed so that they can be moved into position. When positioning your hose clamps on your new hose, be sure they are behind the flange of the port to create a proper seal and tighten them by hand until they are snug.
Once your new hose has been installed, you can refill the cooling system with coolant and run the vehicle to ensure it is adequately filled. In some cases it may be necessary to bleed air from the cooling system after service, but the service manual for your vehicle should provide this procedure if needed. Failure to bleed the cooling system could result in bubbles or pockets of air that may lead to overheating or other system problems. Run your vehicle and check the new hose for signs of leaks near the clamps to ensure that they are properly secured, and the job is done.
Your cooling system is one of the most important parts of your vehicle, and keeping it working properly and inspecting it regularly should always be a priority. Even small leaks from your radiator hoses, heater hoses, or bypass hose can quickly lead to overheating and engine damage, and sudden failures due to old or worn out hoses are easy to avoid with basic maintenance and regularly-scheduled hose replacements. Most manufacturers recommend replacing rubber components like hoses every 60-90 thousand miles, but any signs of failure should be addressed and parts replaced as soon as possible, regardless of your vehicle’s mileage. Keeping an eye on the condition of your radiator hoses and cooling system can help keep you on the road and driving with peace of mind. You can learn more about cooling system repair in our How-To Hub, and find the radiator hose, heater hose assembly, or even cut-to-size bulk coolant hose you need at your local O’Reilly Auto Parts.