My TO-20 is overheating; how is a new thermostat supposed to be installed, and what else could be causing overheating? November 16, 2016.
See the attached information on the thermostat position, The pointed end should be pointing towards the radiator.
As for other causes you may just have an air lock in the system. I always leave the pressure cap off, and watch the coolant level go down when the thermostat opens, and then you should see the turbulence in the coolant as the coolant begins flowing through the radiator. Once it is showing good flow you can put the cap back on.
The TO-20 uses a 4 lbs pressure cap.
You can test the thermostat with a pail of water, and a thermometer. When the water is 155-165 degrees the thermostat should start to open. It should be fully open when the water temperature is 185-195 degrees.
A collapsed radiator hose, either upper or lower, can restrict the flow of coolant. Because the hoses are made up of layers it is possible for an inner layer to collapse, and restrict the flow while the outer layer looks fine.
Other causes include a loose fan belt, a clogged radiator core, or clogged fins. A visual inspection with a trouble light or flashlight should help determine if the fins are clogged. They can usually be cleaned with a hose or with compressed air. If the fins are bent or crushed they can often be restored using a pair of needle nose pliers, and a screwdriver or a radiator fin comb. A clogged radiator core can often be cleaned by removing the hoses, and back flushing the radiator. The block should also be flushed. Plain water is usually sufficient, but there are also flushing compounds available at a local auto parts store. In extreme cases a radiator shop may have to remove the tanks, and rod the core. A radiator shop can also flow test the radiator to see if it is flowing like it’s supposed to.
A water pump can be defective even if it does not leak. Early water pumps have stamped brass impellers which corrode. Later model pumps use cast iron impellers which last longer.