WHEN DO HOSES FAIL
Traditionally, hoses have been visually inspected for failure from the outside. But with today's cars, that method isn't always the best since hoses usually fail from the inside where weakened elements can't be seen and their symptoms not always obvious.

Therefore, inspection of all coolant hoses is critical once the vehicle is 6 years old or nearing 100,000 miles, regardless of physical appearance.

The materials now used in your engine's construction are different than those of years ago. Cast iron has been replaced with aluminum, plastic and brass. Used together with the coolant, which is also conductive, these dissimilar materials can create an electric current. This electrical current can create tiny cracks in the hose tube which eventually weaken and cause the hose to fail. This phenomenon is called electro-chemical degradation (ECD). The coolant seeps through these cracks and attacks the hose reinforcement causing hose to fail.

The Dayco coolant hoses are manufactured with EPDM compound that is electro-chemical resistant (ECR).  Today’s Dayco radiator hoses carry the ECR logo on the labeling for quick identification. 

The higher operating temperatures in cramped engine compartments result in hotter temperatures for hoses. While increased temperatures result in greater engine efficiency, heat also increases the rate of ECD in hoses.  In fact, for every 18-degree increase in temperature, the rate of ECD doubles.

Vibration from rough idling engines weakens other types of hose reinforcements -- again leading to premature failure. Also, abrasion from sharp surfaces within the engine compartment can slowly rub through the outer cover of the hose, eventually causing it to burst. Cuts and nicks on the outside of the hose also contribute to premature failure, but oil is a more common threat. A hose exposed to oil will be prematurely weakened since the oil actually attacks the rubber compound on the hose cover. Any of these signs indicate a hose that could fail at anytime.

SQUEEZE TEST
The best way to check coolant hose for the effects of Electro-Chemical Degradation (ECD) is to squeeze the hose near the clamps or connectors using the following procedures:

1.Make sure the engine is cool.
2.Use fingers and thumb to check for weakness.
3.Squeeze near the connectors. ECD occurs within two inches of the ends of the hose -- not in the middle.
4.Check for any difference in the feel between the middle and ends of the hose. Gaps, or channels, can be felt along the length of the hose tube where it has been weakened by ECD.
5.If you feel any popping or cracking of the hose reinforcement within the hose, it will need replaced
6.If the ends are soft and feel mushy, chances are the hose needs replaced