Hose failure symptoms

With today’s smaller engine compartments, coolant hoses come in all shapes and sizes to fit specific applications and tight engine spaces. They carry coolant to a variety of under-bonnet equipment and consist of three parts: the tube, reinforcement and cover.

While basic hose design has remained relatively unchanged over the years, hose materials have improved substantially. Thanks to these improvements hoses last longer today than before. Yet, their harsh working environment will inevitably affect them and over time even the best hoses will wear and need replacement.


Here, we explain how to inspect and diagnose failed automotive coolant hose. Some general guidelines to start your hose inspection:

  • Always check for kinking
    When inspecting a coolant hose for damage, make sure that it is not kinked, and is not touching hot or moving engine parts or sharp edges. A kink can reduce the flow of coolant and cause the engine to overheat. A sharp surface may eventually cut or abrade through the hose, resulting in a loss of coolant.
  • Additional tip: checking the hose temperature can reveal if the system is functioning properly
    Let us give you some examples. Use an infrared thermometer to read the hose temperature. If the heater is on, both the ingoing and outgoing heater hoses should be close to the same temperature. If not, it might be time for a repair. If the upper radiator hose already gets hot before the engine has properly warmed up, it means the thermostat is not closing properly or even is constantly open. If it does not get hot at all, it means the thermostat is blocked. In both cases, the thermostat should be replaced immediately.

1. Electrochemical degradation (ECD)

Appearance: The number one cause of hose failure! Using your thumb and finger, squeeze the hose near the connectors, ECD initially attacks within two inches of the ends of the hose. If the ends feel more soft and mushy that the middle or if you feel gaps or channels inside the hose, it is most likely under attack by ECD.

Cause: Different kinds of metals in the cooling system generate an electrical charge, which is carried from one component to another by the coolant. This electrical charge can weaken the hose by creating tiny internal cracks in the hose.

Solution: Replace the damaged hose immediately. The best way to avoid ECD failure is to install a hose that fights ECD. Gates electrochemical resistant hoses are your best protection against electrochemical degradation.


2. Leakage

Appearance: Moisture, drips or coolant bleed marks on or around the hose clamps, connectors or on the hose itself.

Cause: Insufficient clamp torque, deterioration of the hose or connector.

Solution: Retighten adjustable tension clamps after a brief run-in period. Alternatively, use constant-tension clamps, which automatically adjust with the heating and cooling of the system. A beaded connector offers better sealing and retention characteristics. Brass and cast iron fittings adhere to common rubber compounds after time, which reduces possibility of leaks, as does the use of sealants and viscous gels. Replace with the recommended Gates hose. Gates uses compounds that offer better resistance to the negative effects of compression set.


3. Heat damage

Appearance: Slight swelling is one sign of internal damage. A hardened, glossy cover that is covered with cracks is a sign of external damage.

Cause: Engine heat, low coolant levels and/or temperature spikes also contribute to deterioration.

Solution: Replace with the recommended Gates hose. Gates hoses are specially designed to resist deterioration from heat.


4. Ozone damage

Appearance: Tiny, parallel cracks in the cover, usually at hose bends.

Cause: Increased concentrations of ozone, caused by pollution, attack  bonds in certain rubber compounds. Tiny cracks occur allowing contaminants to invade and destroy the hose.

Solution: Replace with the recommended Gates hose. Gates hoses are made of EPDM and are unaffected by ozone.


5. Abrasion damage

Appearance: Rubbing marks on, or damage to, the hose cover.

Cause: Abrasion damage is caused by hose rubbing against other engine parts or against objects in the environment.

Solution: Replace the hose. If the hose is resting on or will come into contact with a sharp surface, or is near a heat source, try one of the following: 1) Reroute the hose or replace/repair the hose guiders 2) Slightly twist the hose on one or both spouts to reroute the hose 3) Wrap a protective sleeve around the new hose at the point of contact. Avoid using a slit piece of an old hose, as this will negatively influence the system’s overall temperature.


6. Oil contamination

Appearance: The hose feels soft or spongy to the touch. Bulges and swelling are readily apparent.

Cause: Oil reacts chemically with the hose compounds and weakens the molecular bonds. This causes the hose to soften, swell and separate, layer by layer, leading to failure.

Solution: Replace the hose and eliminate any source of oil. If this is not possible, reroute the hose.