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When Is It Time To Replace My Coolant Hoses?

Automakers don’t specify a mileage when coolant hoses should be replaced. We discuss what they do, how they wear, and how to visually spot when it’s time to replace them.

Carmakers do not consider coolant hoses a routine maintenance item, so it follows that there can be a lack of guidance about how often these hoses should be replaced. Without a specific mileage point or time interval to use as a reference, it's crucial that you stay informed about how coolant hoses work and how they wear out. In this article, we'll focus on what coolant hoses do - and how to recognize the warning signs that it's time to replace them.

What Coolant Hoses Do

Radiator and Heater Hoses

In a typical automotive cooling system, you'll find at least 4 main hoses. First, the upper radiator hose leads directly from the thermostat housing (on the intake manifold or cylinder head) into the top of the radiator. Attached to the bottom of the radiator is a lower radiator hose. Drawn by the engine's water pump, this coolant has shed most of its heat when it passed through the radiator. This hose and the upper radiator hose are the largest of the cooling system hoses, and are both attached to the front of the engine block.

Typical Automotive Cooling System

Next, there are two smaller heater hoses which lead to and from the heater core located under the dashboard which supplies warmth to the passenger compartment.

Coolant Bypass Hoses and Pipes

A typical coolant bypass hose.
A coolant bypass pipe, shown detached in black.

Until engine coolant has heated up after a cold start, the thermostat remains closed - directing coolant back to the engine block instead of to the radiator. When this happens, the coolant flows through an externally-mounted coolant bypass pipe or bypass hose. As it sounds, bypass "pipes" are rigid, non-flexible tubes made of steel or plastic - while bypass "hoses" are traditional rubber compound hoses. The design of this coolant return setup varies from automaker to automaker. Bypass returns are generally short in length and are often considered a "fifth hose".

BMW V8 Coolant Bypass Pipes In Internal Difficult To Reach Locations
Although not commonplace, some engines such as this BMW V8 position their coolant bypass pipes internally in difficult-to-reach locations.

Instead of an externally-mounted tube or hose, some engines go a step farther and use internal passages cast into the front housing of the engine for the return coolant to flow through. Inside this passageway will be a dedicated pipe for the coolant. One such example is found on BMW-sourced V8 and V12 engines.

Overflow Hoses For The Reservoir Tank

An overflow hose runs between the radiator cap and the reservoir tank where extra coolant is stored (and added). As pressures within the cooling system change with coolant temperature, a valve in the radiator cap allows coolant to flow back into the reservoir to relieve pressure buildup which naturally occurs.

Overflow Hose For Reservoir Tank

Conversely, if coolant has contracted during cold temperatures, more of it can easily be drawn out of the reservoir tank to keep the system pressurized. Reservoir tanks also feature their own pressure cap - which should not be opened while the coolant is hot.

Why Coolant Hoses Wear Out

In order to withstand the vibration and movements of the engine without breaking, cooling system hoses must be flexible. To achieve this, traditional (and OEM) coolant hoses feature outer layers made of a durable rubber compound. Underneath the rubber outer layer is a flexible fabric reinforcement mesh. The mesh is designed to withstand high levels of heat and pressure.

Typical Coolant Hose Made Of Strong Fabric
A typical coolant hose features strong fabric mesh integrated into the rubber.

Thanks to advanced polymers and compounds, the rubber compounds and fabric mesh of today's coolant hoses lasts a lot longer than those from decades ago. But eventually, the hose weakens and wears out over time - primarily because of electrochemical degradation that can result between the hose and metals in the engine that work their way into the coolant. If coolant gets dirtier and more contaminated because it isn't changed at specified intervals, the excess metals in the coolant create a mild electrical current flow throughout the cooling system - allowing coolant to penetrate the hose and weaken it.

Coolant Hose Degrated From Outside
This coolant hose degraded from the outside.

Coolant hoses also degrade when their outsides are exposed to direct contact with oil or other contaminants. This can occur, for example, when hot oil drips onto the rubber from a leaky engine. Also keep in mind that in addition to hot coolant from within, excess engine compartment temperatures can stress the rubber compounds.

Failed Coolant Hoses
Some examples of failed coolant hoses.

As all of these issues occur, small cracks in the rubber develop and get worse over time. Ultimately, the hose can split and leak, or form a mushy blister which can burst at any point.

Typical Lower Coolant Hose With Internal Spring
A typical lower coolant hose, with an internal spring to prevent hose collapse due to suction from the engine's water pump.

Note that because lower coolant hoses are exposed to heavy amounts of suction from the engine's water pump, a resilient spring is wound around the inside of them to ensure the hose does not collapse and block the flow of coolant. Like most components of modern hoses, these springs are quite durable over the long term. However, a lower coolant hose that has buckled inward or collapsed in spots is a clear sign it needs to be replaced immediately.

Checking The Condition Of Your Cooling System Hoses

A quick examination of your hoses to check their condition can easily be performed without removing them. Wait until the engine's been off long enough to cool down, then squeeze each of the hoses in various spots. Firm hoses that quickly pop back to shape signify the rubber is in good condition, while a hose that feels spongy or doesn't bounce back means the rubber has dried up due to age and is more prone to cracks and leaks. Older hoses that have hardened tend to weep and leak coolant around the attachment areas first, so look for this.

If you get a "crunchy feel" when squeezing the hose, it's a clear sign the fabric mesh underneath has become compromised enough to crackle and/or break apart. Such a hose should be replaced as soon as possible.

Cracks or splits on the outside of the hose visible to the naked eye are another sure sign that a hose needs immediate replacement. And, as we mentioned before, if you see any oil contamination on the outside of a hose, clean it off and feel the rubber. If any mushy spots exist, the hose has become severely weakened.

Swollen Lower Hose
The lower hose has become swollen and will need to be replaced.

A hose that has become swollen signifies the inner fabric mesh has worn in that spot, and the hose has become compromised. If it isn't leaking already, odds are good that it can seep or burst without warning.

If you see any visible coolant leaks in the middle of a hose, replace it immediately. For leaks that are emanating from the ends of the hose, check the clamp tightness as well as the hose underneath that section.

Opportune Times To Replace Coolant Hoses

The underhood inspection is a reliable way to check your hoses. After all, most of them are readily accessible in the engine compartment (and we again remind you to perform the check on a cold, not hot, engine.) But why wait until the hoses are about to fail? Experience has taught us that all coolant hoses need to be replaced eventually. Consider these facts:

  • The coolant must be drained to replace the hoses.
  • The hoses must be disconnected when replacing a radiator, water pump, thermostat, or heater core.
  • A blown hose can cause the loss of most or all of your engine coolant, which then leads to overheating, which damages other components in turn.

There is something to be said for the idea of pre-emptively replacing these hoses BEFORE they fail. Depending on your vehicle's age and mileage, speak to your car care professional. Replacing all the hoses (and clamps) when the coolant is flushed is one example of a sensible pre-emptive replacement. If you have purchased a used car and are unsure of its repair history, you might want to play it safe and install all new hoses. Of course, if you're doing this work yourself, all the better, as you can set your own interval (100,000 miles/10 years is a good benchmark) for replacement.

Coolant Hoses We Offer

To help you get a general feel for what's available, we mention some of the various hoses we offer on our website below. But we also recommend entering your year, make, and model in our SELECT VEHICLE box along the top of the screen, then pressing the "Go" button. Our website will automatically narrow your search down to hoses and related products specifically designed for your car or truck.

Coolant Hoses Select Vehicle Box

Radiator Hoses

When it comes to radiator hoses, we've got a selection of upper and lower hoses for a wide range of vehicles from Continental ContiTech, AC Delco, and Dayco. Ford owners will find a good selection from Motorcraft, and Jaguar & Land Rover owners will find upper and lower radiator hoses from Eurospare. European car owners will find upper and/or lower hoses from Vaico for such vehicles dating back to the 1980s. For select water-cooled Porsche models back to 1986, we've got German brand hoses. Hyundai and Kia owners can access radiator hoses for a range of years and models from Auto 7.

Heater Hoses

For a wide variety of vehicles, we've got heater hoses from Dorman, Genuine, URO Parts (European makes back to the 1950s), Motorcraft (Ford models), Continental ContiTech, HPS, and Dayco.

Manufacturers that specialize in heater hoses for certain vehicles are Eurospare (older Jaguars & Land Rovers), AC Delco (various GM models), OPGI (classic GM vehicles), Crown (1980s-90s Jeep models), and Omix-ADA (Jeep models back to the 1940s),

Overflow Hoses

We've got coolant reservoir overflow hoses from Motorcraft (select Ford models), OPGI (select GM models 1950s-80s), URO Parts and Genuine (both cover Mercedes back to 1965), Eurospare (Jaguar/Land Rovers), MTC (Volvo or VW), and AC Delco (select GM models) - among others.

Coolant Hoses Variety Gallery

If you do end up needing to replace one coolant hose, we strongly recommend replacing all of them - along with hose clamps that hold them in place. Since you'll need to drain at least some of your coolant out during hose replacement, it's also a great idea to replace your engine thermostat if it's got over 100,000 miles on it. We say this because compromised hoses can release gunk into the system which gums up and shortens the life of of other components. This helps ensure that you avoid an engine-damaging overheating situation. While you're at it, replace the pressure caps for the radiator and overflow tank too.

We're here to help with any questions you may have on the thermostats we sell, so give us a call seven days a week!

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