Chevelle running hot

[70SS454]

I have not had my 70 chevelle long. This is the first warm weather I have driven it in. Today my 454 really started running hot while sitting at the light. It usually runs around 200-220 degrees. It was headed over 240 on its way up. It's a Texas car now and was in Wyoming most of its life. It dumps the antifreeze overboard when it warms. There is no resivoir on it. Should there be one? Do I need a differrent thermostat? I think it would have given me a temp light if I had to is t much longer.