Until recently, the most common method of checking an engine coolant hose was by visual inspection of the outside cover for signs of wear. Obvious signs of "ballooning" under pressure and "physical damage" are easy to spot, but what you can't see is what you really need to know about. Resent research has shown that most hoses fail from the inside out.

Inside Knowledge

During a four-year field test 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 begins to seeps through these cracks and attacks the hose reinforcement. The braided reinforcement acts as a wick along the length of the hose, providing an avenue for the coolant to migrate. The condition eventually results in a pinhole leak or a burst hose.

Like oxidation, ECD is accelerated by certain 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 most severe damage occurs where temperatures are the hottest and air is present with the coolant, which is why upper radiator hoses tend to fail first.

Testing Your Hoses

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:

• Make sure the engine is cool.
• Use your fingers and thumb to check for weakness, not the whole hand.
• Start by squeezing the hose near the ends at the connectors. ECD occurs within two inches of the ends of the hose.
• 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.
• If the ends are soft and feel mushy, chances are the hose is under attack by ECD. To avoid breakdowns, replacement is recommended.

4-Year Old Rule

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 vehicles that are subject to significant stop-and-go driving and the resulting high engine and coolant temperatures.

Alternatives to Standard Hoses

Alternatives to standard coolant hoses are "custom" hoses or "hard" hose. An Example of "hard" hose would be Cool Flex. Cool-Flex Fluid Transfer Hoses are constructed from seamless corrugated copper tubing, and are specifically designed to withstand high vibration and high-pressure situations.

They will accept any bend necessary and they hold there shape indefinitely and never collapse. (Left)

The construction is impervious to elements such as oil, heat or any engine fluids. It's also non-corrosive and actually helps dissipate engine heat. Cool-Flex Fluid Transfer Hoses, also come with a Lifetime Guarantee.

Another alternative is custom, braided hose. This type of hose is made of rubber that is bonded to a braided stainless steel outer jack. These hoses over time do ware out, but they are able to withstand heat and oil exposure better and longer than standard hose. The braided outer jacket helps reduce pressure strain on the tube. (Right)

Still, another alternative is the recently introduced, Electrochemically resistant (ECR) hose has been developed by Gates engineers to resist the destructive effects of ECD. This new product, which is expected to evolve into the industry standard, carries the ECD-resistant properties of silicone hose, without the susceptibility to punctures and tears.

Goodyear Tire & Rubber Company has marketed hoses that are EPDM based for several years now. Starting with their Super Hi-Temp Royal Blue® EPDM hoses in the early 1990's to their latest line of Super Hi-Miler® high heat-resistant hose which is designed to provide superior performance over standard EPDM hoses at a substantially lower cost than Silicone based hoses. Goodyear backs their product lines with a Lifetime Replacement Guaranty, making the the higher cost more palatable.

These newer compound hoses do carry a higher price than standard hoses. Generally these hoses are 25% to 40% more than the standard quailty hose. However, with a replacement interval of over 200,000 plus miles, they last much longer than standard 4 year hoses, thus provide a long term cost savings and reduced maintenance. The reliability aspect should not be overlooked as well. Backed with a full replacement guarantee, the added investment is well worth it. So, get out there under the hood and squeeze.