Silicone stays flexible across a wide range, but flexibility is not the same as stretch. In the cold the material is stiffer, so a hose that slips onto a bead easily in summer has to be pushed with far more force, and that force goes into the bead rather than into the hose wall.
That is the mechanism behind most cold-weather hose damage: not a hose that splits on fitting, but a hose whose inner layer is shaved by a bead it was forced over, which then fails much later when the shaved area softens and the clamp can no longer seal it.
Warm the hose, not the engine bay. A hose kept somewhere warm for a while before fitting is soft throughout and slides on without local force. Warming the bay instead softens nothing and adds the risk of working close to hot or moving parts.
Keep the hose sealed until the moment of fitting. A hose that has been lying open in a cold workshop takes on the shape it was stored in, and a flattened or kinked hose will not seal on a round bead no matter how warm it becomes.
A little lubricant on the inside of the hose helps, and where it goes matters more than what it is. Lubricant on the bead lets the hose slide on; lubricant on the outside of the hose lets the clamp slide off. Keep it inside, and wipe the outside before the clamp goes on.
Avoid lubricants that leave a residue the hose will absorb. Silicone hose is porous to some oils over time, and an oil-based lubricant left on the inner surface will soften it from the inside, where you cannot see the damage forming.
On a cold joint the clamp position matters more, because the hose is less willing to conform. The band should sit behind the bead, fully on the hose, with the whole band width covering hose rather than hanging over the end of the bead where it has nothing to compress against.
Mark the position before the hose goes on, then check it by feel afterwards. A cold hose hides the bead under its own thickness, and a clamp that is only half on the bead will hold pressure at idle and slip under load.
If the hose will not go on, do not reach for a bigger lever. Check the bead first for a burr or a rolled edge, then check the hose bore against the pipe it is going onto. A mismatch of a fraction shows up as a hose that will start onto the bead but will not seat behind it.
On a performance silicone hose with a reinforced wall, the reinforcement limits how far the hose can be stretched, so a bore that is close but small will not stretch over the bead the way an unreinforced hose would. Where the joint is a hard one, a heavy duty silicone tube with a thicker wall is the part to use, rather than a thinner hose forced into place.
After a cold fit, run the engine up to temperature and let it cool fully before checking the clamps. The first heat cycle lets the hose relax onto the bead, and a clamp that felt tight when cold will often feel loose afterwards.
Check again after the system has cooled. A hose that has seated correctly will still be under the clamp with the band in the same place; one that has crept will show a gap between band and bead, and that is the joint to redo before it becomes a leak.
