Coolant hose failure

[Angeo]

Hot News About Coolant Hose Failure


Coolant Hose Failure Is Linked To Electrochemical Attack...
Until recently, most coolant hose failures were generally thought to be caused by heat cracking, yarn failure and cold cracks. Now, after years of testing, engineers with The Gates Rubber Company in Denver, Colorado, have identified the primary cause of failure as an "electrochemical attack" on the tube compound used in upper radiator, bypass and heater hoses. The following report describes this phenomenon and what it means.

Since the 1960s, manufacturers have made automotive coolant hoses using EPDM (ethylene propylene rubber) compounds known for their resilience and flexibility. The failure of these qualities, indicated by the appearance of bulges or cracking, always has been a sure sign that it was time to replace a hose.

In recent years, however, service technicians around the country have been confounded by the unexpected failures of radiator, heater and thermostat by-pass hoses in relatively low-mileage passenger vehicles. Often these failures occurred with little or no sign of exterior deterioration of the hose.


The Problem Defined
The first insight into the cause of these unexplained failures came when a special team of Gates engineers identified the primary cause of coolant hose failure as an electrochemical attack on the rubber tube compound in the hose.

This phenomenon is known as electrochemical degradation, or ECD. It occurs because the hose, liquid coolant (ethylene glycol antifreeze and water), and the engine/radiator fittings form a galvanic cell or "battery."

This chemical reaction causes microcracks in the hose tube (see Figure 1), allowing the coolant to attack and weaken the hose reinforcement. Accelerated by high-heat and flexing, the hose can develop a pinhole leak or rupture under normal pressure.


Figure 1
ECD damaged hose.


Contributing Factors
During four years of field testing on fleet vehicles with various mileages, nearly all of the vehicles were found with some degree of electrochemical degradation. Generally, upper radiator hoses and heater hoses showed more damage than lower hoses with the most severe damage observed in the tube area within one to two inches of either end of the hose.

Engine hoses that are subjected to any extended amount of stop- and-go, engine idle or "on-off" conditions showed earlier and more severe electrochemical damage.

On older model vehicles, the bypass hose is especially subject to electrochemical attack, aggravated by the extremely high temperatures passing through a smaller radius hose. Usually, the smaller the dimension of the hose, the faster ECD damage occurs.

In addition, the hose that is most likely to contain air when the vehicle is not running -- the upper radiator hose -- usually shows the most damage.


Preventing Failure
Gates engineers emphasize that it's not uncommon to find premature hose failures due to electrochemical damage in vehicles driven less than 25,000 miles. From the customer's perspective, the timely replacement of a coolant hose can prevent an emergency breakdown on a highway, as well as costly engine damage. Today's engines run at higher temperatures, which means if the hose fails and coolant is lost, overheating occurs almost immediately.

To address the damage caused by ECD, Gates also developed an electrochemically-resistant coolant hose using a new EPDM formulation. The new EPDM hose offers improved performance characteristics over standard rubber hose.

In fleet tests in the toughest applications, ECR hoses have gone 200,000 miles and are still going with no electrochemical damage. Standard hoses revealed damage and failures as early as 20,000 miles in the same fleet tests (see chart).




To be safe, Gates recommends changing coolant hoses if they are four years old, or older, especially the upper radiator and heater hoses.

Of importance to technicians and car owners is the superior bonding ability of the EPDM hose to metal fittings. Gates new ECR hose also inhibits water in the coolant mixture from permeating through the hose wall. Water loss can cause an imbalance of the antifreeze, which has an adverse effect on the freezing and boiling points.

Whenever replacing a hose, Gates also recommends replacing the clamps. Although today's clamps are generally made with stainless steel bands that resist corrosion and damage, they're held in place by a carbon steel screw which can fatigue and lose strength.