When a hose fails, the first question is usually “was it a bad hose?”. Nine times out of ten it was a specification that did not match the service.
A hose is rarely “faulty”. It is a part that was asked to do something its compound, wall or construction was not chosen for. The seven modes below cover almost everything we see, and each one has a specific answer at the specification stage.
Rubber hardens as it ages. The plasticiser migrates out, the surface goes glossy and then cracks, and the hose stops sealing. EPDM is comfortable to roughly 120–150 °C; silicone holds to about 200 °C. Beyond that, or after enough cycles, both will eventually fail.
Specify: the continuous temperature, the peak temperature and how long the peak lasts. “Up to 150 °C” means nothing without the duty cycle.
The wrong compound absorbs the fluid, swells, softens and loses strength. EPDM is excellent in water, coolant and glycol, and poor in oil and fuel. Nitrile handles oil; FKM handles fuel and aggressive chemicals.
Specify: the exact fluid, its concentration, and whether it is a mixture. “Coolant” is not enough — the glycol type and ratio matter.
The hose does not leak where you can see it; the fluid passes through the wall molecule by molecule. On a long coolant loop over years, that is a measurable loss, and on a sealed battery cooling circuit it becomes a service issue.
Specify: a low-permeability compound, or a thicker wall. Both cost a little more and both work.
Most engine-bay hoses do not fail from the inside. They fail from the outside, where they rub against a bracket, a hose clip or another hose. A 1 mm deep scuff removes the outer protective layer and starts a crack.
Specify: a protective sleeve, a different routing, or a reinforced outer cover. Also tell us what the hose runs against — that single sentence changes the recommendation.
The end of a hose is where stress concentrates. Under continuous vibration, the reinforcement fatigues and the hose fails just behind the clamp — often at a few thousand kilometres.
Specify: vibration, whether the hose is rigidly mounted, and whether a hump or bellows section is needed to take up movement.
If the installed radius is tighter than the hose can take, the wall collapses on the inside of the bend. Flow drops, the bore narrows, and the reinforcement on the outside is over-stressed.
Specify: the bend radius of every bend, measured to the centreline — not the radius of the space you have.
Leaks at the joint usually come from the end form, not the hose. A plain cut end under a spring clamp creeps; a beaded end does not. The wrong clamp on the wrong end is a guaranteed leak.
Specify: how it attaches — beaded for a spring clamp, barbed for a push-on, flanged, or fitted with a connector — and which clamp is used.
Most of these are a single line on an enquiry. Sending them costs two minutes and removes most of the risk of a part that fails at 3,000 km instead of 300,000.
With those seven answers we can usually recommend the compound, the construction and the wall in one reply — and tell you honestly where the limits are. If a requirement is going to be difficult, you hear it at quotation stage, not after the fourth batch.
Send a drawing, a photo with a ruler, or the old sample. We reply with a price, a lead time and the questions we need answered.