Car getting real hot....

As a note, I had a 69 Chev heavy 1/2ton with a 292. In winter the heater would not put out heat. Now you need to know we get minus 35°C to 45°C in January and February. Looking at the bypass hose on a 250 six, it was 5/8" hose. The bypass on the 292 six was 3/4" or 1". Driving on the hyway the rad coolant was getting over cooled and windchill on the block kept the thermostat almost closed. All the coolant was bypassing, and the little that went to the heater bately took the chill off. I took the bypass hose off and put a flat washer in that would be trapped and restrict the bypass. Then I got heat!
Another problem on that used truck was poor previous maintenance. I flushed the cooling system once a week for a month and it kept getting rust red. I finally put a remote oil filter in the heater hose line with valves so I could change the filter without draining the coolant. It did not take long for the turbulence to pick the settled rust out of the block and filter it out. Then the coolant stayed nice and clear.
Just a maintenance tip for those with a similar problem. Once the cooling system is cleaned out, the filter can be removed.