After driving many Mustangs myself, my twins now have their first Mustangs. One started showing a maxed temp gauge so I asked my mechanic nephew to take a look. The engine wasn't hot even though the gauge was full H. He said the lower radiator hose was hot and the top hose cold so we replaced the thermostat.
The gauge still shows max H but the engine is still not hot. The top radiator hose is fairly hot but the bottom hose is cold. The coolant in the reservoir on top of the engine is cold as well.
Does anyone know if the water pump pushes water from the bottom of the engine to the top or pull it from top to bottom?
Any suggestions on what the problem could be?
1. The water pump draws cooler water from the lower radiator hose, pumps it around the engine where it absorbs heat, and the hotter water exits the engine from the upper radiator hose.
2. The water in the lower radiator hose is always cooler than the water in the upper radiator hose in a running engine, as the water circulates from the top of the radiator to the bottom and sheds heat.
3. It's extremely rare for a mechanical water pump to fail completely. They will usually leak from the weep hole when the pump shaft seal perishes.
4. A thermostat stuck closed would prevent coolant from reaching the upper radiator hose, so that would remain cold and soft.
5. The coolant temp. gauge measures cylinder head temperature, and the sending unit is in the valley underneath the intake manifold.
6. If the gauge shows H right from a cold start, either the gauge sending unit is faulty or the gauge stepper motor is stuck. With the latter, the gauge would still be on H even with the ignition off.
7. Use an infrared temp. gun to check the temp. of the upper & lower radiator hoses as the engine idles from a cold start to normal operating temp., and report back.