Radiator Hose Coils

Automotive Mileposts
Image: Molded radiator hose

Molded radiator hoses like the one pictured above often had a
coil in them when factory installed, but replacements usually don't

There's supposed to be a spring in this hose, isn't there? The one I just took off had a spring, so this can't be the right part...right?

Original equipment molded radiator hoses often were equipped with a coil inside them. Some refer to this coil as a spring, but it isn't really a spring. Actually just a piece of thin metal rod that has been twisted, it was designed to facilitate the installation of coolant on the assembly line, and nothing more.

When the cooling system of a car is completely drained, or in the case of a brand new car under construction, never had coolant in it, there is a considerable amount of air in the passage ways. Normally, when filling up the cooling system, you start the car to circulate the coolant, displace trapped air, and then top it off. On the assembly line, this wasn't feasible, so air in the cooling system was evacuated by essentially pulling a vacuum on it. This also had the added advantage of speeding up the introduction of the coolant mixture to the cooling system as well. The coil in the lower radiator hose prevented the hose from collapsing under this higher than normal vacuum.

Once the car left the factory, the coil served no further purpose. This is why replacement hoses usually do not have a coil in them. Most cooling systems operate at 12-15 P.S.I., which is controlled by the radiator cap. This is enough pressure to allow a normally functioning cooling system to operate efficiently, yet not enough to cause collapsed hoses or leaks in seals if they're in good condition. If the lower radiator hose collapses, it is normally due to a fault somewhere else in the system, and is not necessarily indicative of a bad hose, although an old hose certainly might be susceptible to collapse due to age. Normally, if the hose is in good condition but collapsing and blocking the flow of coolant, the radiator cap is bad or there's a blockage somewhere else causing pressure to build up in the cooling system.

As vehicles with original hoses began to age, the coil would sometimes begin to corrode and deteriorate, circulating tiny pieces of metal throughout the cooling system. We'll leave it to your imagination what this did to water pumps and thermostats.

This is just one of many interesting stories about automobiles, the people who build them, and how they were built, brought to you by Automotive Mileposts.