Hoses are the cooling system’s weakest structural component. They are made of flexible rubber compounds to absorb vibrations between the engine and radiator, or, in the case of heater hoses, the engine and body’s firewall. Designed to hold coolant under pressure, hoses are also subjected to fluctuating extremes of heat and cold, dirt, oils, and sludge. Atmospheric ozone also attacks rubber compounds.
The most damaging cause of hose failure—electrochemical degradation (ECD)—isn’t easy to detect. According to engineers for the Gates Corporation, a parts maker, ECD attacks hoses from the inside, causing tiny cracks. Acids and contaminants in the coolant can then weaken the yarn material that reinforces the hose. Eventually, pinholes can develop or the weakened hose may rupture from heat, pressure, or constant flexing.
Some easy, basic maintenance can help prevent coolant hose failure:
- Check the white coolant-recovery tank often to ensure proper fluid level. Marks on the tank indicate the proper level for when the engine is cold or hot. If the tank is low after repeated fillings, suspect a leak. Also check for white, light green, blue, or pink coolant tracks in the engine bay, which is residue left from leaking coolant.
- When the engine is cool, squeeze the hoses with your thumb and forefinger near the clamps, where ECD most often occurs. Feel for soft or mushy spots. A good hose will have a firm yet pliant feel.
- Inspect for cracks, nicks, bulges usually while hot), or a collapsed section in the hose and oil contamination, or fraying near the connection points.
- Look for parallel cracks around bends (caused by ozone), a hardened glassy surface (heat damage), or abrasive damage (hose is rubbing).
- Flush and replace the coolant according to the owner’s manual. Clean coolant is less likely to support ECD.
- Never remove the radiator cap when the engine is hot, as the hot coolent will be under pressure. Also, be aware that an electric cooling fan can come on at any time.
The upper radiator hose fails more often than any other hose, followed by the water pump bypass hose (if your vehicle is so equipped), and the outlet heater hose from the engine to the heater core. Experts recommend, however, that all hoses be replaced at least every four years or when one fails. Always use replacement hoses designed to fight ECD. Trademarks will vary among hose manufacturers. (Gates uses “ECR” for Electro-Chemical Resistant). Look for a “Type EC” label on the hose or its packaging. That is a Society of Automotive Engineers standard signifying “electrochemical.” Most vehicles built after 1993 come with ECD-resistant hoses.