Changing Cooling System Hoses and Thermostat
| 01 February 2002
In December 2001, the Pony Trick pertained to changing antifreeze. This trick provides some tips that have worked when changing hoses and the thermostat:
Fit and coolant-flow are more predictable if preformed hoses are used in the same locations where the factory used them. Preformed hoses are used for upper and lower radiator hoses, the bypass hose, and, in certain models, some of the heater hoses.
When replacing hoses, replace ALL hoses at the same time. Retaining an old section of hose can invite failure. For example, don’t overlook the little bypass hose.
Old hoses like to stick to the nipples where they attach. One way to remove a stubborn connection is to cut the hose off just beyond the nipple. On the piece that remains, use a sharp knife to make a full length cut in a direction parallel to the axis of the nipple. Use your fingers or a pair of pliers to grasp the cut edge and then peel the piece of hose off the nipple. Be careful to not cut or damage the nipple.
Clean nipples make for easier assembly and they reduce the likelihood of leaks after new hoses are installed. Carefully clean corrosion and pieces of rubber from all nipples.
Small diameter hoses, like new heater and bypass hoses, sometimes leak coolant after a few heat cycles. A light coating of good gasket sealer (example: Copper Coat) evenly applied to the inside diameter of the hose before assembly usually prevents leaks.
Stainless steel spiral-screw-clamps are probably the best choice for all connections unless concours clamps are required. Tighten clamps snugly. A properly tightened clamp is usually drawn into the surface of the hose by an amount equal to the thickness of the clamp band. After a few heat cycles, check the clamps and tighten any that are loose. Some of the newer Mustangs have special spring steel clamps that should be used in all original locations. No comments will be offered on concours clamps, especially tower clamps, because the descriptive language required is unacceptable in a public forum.
There are several cautions and tricks to consider when changing the thermostat. To help a new gasket seal properly, clean all corrosion and pieces of old gasket material from both the thermostat housing and the surface to which it mates. Install the new thermostat in the proper direction. Some thermostats are marked “rad” or “radiator” to indicate which side goes closest to the radiator. Direction is important even if there are no markings so if you’re not sure, consult a service manual. Install the new thermostat in the proper location (engine side of gasket or thermostat-housing side of the gasket) as defined by the machined circular relief that accommodates the thermostat flange. Use a new thermostat housing gasket with gasket sealer applied to both surfaces. And if the thermostat housing bolts penetrate the engine cooling jacket, apply gasket sealer to the threads before installing them.