[TR] Explain This Overheating

[William Brewer]

     So I've begun driving the TR3 to work again. It has been in the 80's
during the day in Mojave. It is pretty brisk at 0600 at the mile high
elevation that I live at.
     The temperature gauge in the TR3 has lost the
ether and is getting sent in to be rebuilt asap.
     So yesterday I am
driving home. The TR runs like a freight train. I coasted down about 1/2 mile
and downhill and stopped outside my garage. While the garage door is opening
the car overheats and steam comes out.
     I topped off the coolant. Later
that evening I let my daughter drive the TR with me in the car with her. We
are tooling around the hills at low speeds, under 35 mph. We coast down about
a mile of downhill and stop at a stop sign. I begin smelling hot coolant
again. It is like it is taunting me.
     My radiator was rebuilt about 12
years ago without a crank hole.
     I have blocked off the water pump bypass
with a brass plug with a 1/8" hole drilled in it to prevent vacuum lock.
    
I have an electric fan (puller, not pusher) that comes on at about 190.
    
Tonight I am going to use a Prestone radiator flush and refill with fresh
coolant and distilled water 50/50 mix.
     With the coolant out I am going to
pour water in the top to see how fast it sloshes out the bottom hose hole to
see if the radiator appears blocked..

     I only use distilled water and
coolant in my radiator.
     Last year I put on a new Moss radiator cap and a
new 185 thermostat and put on all new hoses.
     My question is, why does it
overheat after a long downhill? I could see it overheating after a long
uphill.
     Gotta get the temp gauge fixed. I meant to do it when the cold
weather arrived.

      -Bill in Tehachapi