Abstract: A radiator hose hydrometer includes a substantially horizontally disposed transparent tubular conduit interposed in the upper radiator hose of a liquid cooled engine. A hydrometer is mounted within the tubular conduit and is comprised of a series of arcuate transparent tubular members having apertures therethrough permitting the free flow of coolant into the tubular member. A float is operably secured within each tubular member, and is formed from a material which will float in liquid of a predetermined specific gravity. Each float is formed from materials having different specific gravities. Printed indicia on the conduit permits determination of the coolant's specific gravity and the coolant's level. Additionally, a radiator hose hydrometer having offset adapter permits use with upper radiator hoses having a diameter different than said conduit for leveling the device.