Coolant Hoses

Taken from Pegasus Pages, the Minnesota Fieros Forever Newsletter March/April2001

 Give the 'squeeze test' to determine potential hose failure

 The coolant circulates from the radiator to the engine and back to the radiator through a series of rubber hoses that are designed to withstand high temperatures and flexing. If any of the hoses fail, especially the radiator hoses, the system will lose coolant, and overheating will result even when the ambient temperature drops below the freezing mark. To avoid being stranded in rush hour traffic or on the open highway, the Gates Rubber Company recommends that coolant hoses be inspected before every seasonal driving change. Until recently, the most common method of checking engine coolant hoses 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 from Gates 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 strands as it wicks along the length of the hose. The condition eventually results in a pinhole leak or a burst 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, driving habits that increase the heat history of the coolant hose accelerates ECD. Therefore, engine hoses that are subjected to an 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 hoses 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. lf 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

Replacement intervals 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, says Gates.

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.