Until recently, the most common method of checking engine coolant hose was to visually inspect its outside cover for signs of wear, or "ballooning" under pressure. This method is no longer considered completely reliable in light of research that proves most hoses fail from the inside out.
Damage starts inside
During four years of field tests on fleet vehicles, engineers for The Gates Rubber Company identified the primary cause of coolant hose failure as an electrochemical attack on the tube compound inside the hose.
The phenomenon, known as electrochemical degradation, or ECD, produces fine cracks, or striations, in the tube wall. These fine cracks extend from the inside to the outside of the hose tube, near one or both ends of the hose. The coolant seeps through these cracks and attacks the hose reinforcement as it wicks along the length of the hose. The condition eventually results in a pinhole leak or a burst of hose at failure.
ECD is not peculiar to any one automotive manufacturer, but is evident in almost all cooling system hoses. The most severe damage occurs where the temperature is hottest and air is present with the coolant, which is why upper radiator hoses tend to fail first.
Like oxidation, ECD is accelerated by driving habits that increase the heat history of the coolant hose. Therefore, engine hoses that are subjected to any extended amount of stop-and-go, or engine idle, show earlier and more severe electrochemical damage.
The "squeeze test"
The best way to check coolant hose for the effects of ECD is to squeeze the hose near the clamps or connectors using the following procedures recommended by Gates:
1. Make sure the engine is cool.
2. Use fingers and thumb to check for weakness, not the whole hand.
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 the ends are soft and feel mushy, chances are the hose is under attack by ECD. To avoid breakdowns, replacement is recommended.
Replace four-year-old hoses
A replacement interval of four years for all coolant carrying hoses--especially the upper radiator, bypass and heater hoses--can help prevent unexpected failure from ECD. The incidence of hose failure increases sharply after four years for most vehicles.
Earlier hose replacement is recommended for fleet vehicles such as taxis, police cars and delivery vans that are subject to significant stop-and-go driving and the resulting high engine and coolant temperatures.
Electrochemically resistant (ECR) hose has been developed by Gates engineers that resists the destructive effects of ECD. This stock, which is expected to evolve into the industry standard, carries the ECD-resistant properties of silicone hose, without the susceptibility to punctures and tears.
In fleet tests in the toughest applications, ECR hoses have gone 200,000 miles and are still going with no electrochemical damage. Standard hoses reveal damage and failures as early as 20,000 miles in the same fleet tests.
Courtesy of The Car Car Council