"Scorcher" Cooling system facts and myths

Long weekend here for Canada Day. Yesterday temperature was over 100 F with humidex. As I pass by the 4 lane HWY on my way to town, I see cars overheated on the side of the road. Happens every year.
So how does your Cooling System work and what fails? When you start your car cold, your anti freeze mixture circulates only in the engine block and heater. (If selected) The water pump moves the liquid from bottom to top of the engine. As the engine reaches operating temperature, the thermostat opens and allows coolant to flow out the top of the engine and into the radiator, where it cools down and returns through the bottom rad hose much cooler. A differential thermostat in the top of the rad switches the fan on when a predetermined high temperature is reached, and it stays on until the lower threshold is met. Another fan or a second speed kicks in when the AC compressor is running. The radiator cap maintains set pressure, usually around 15 Psi, and coolant expansion tank allows coolant to expand and contract as temperature requires. So what fails and why?
1.Rad cap- After they cycle thousands of times they will no longer maintain pressure. For every pound of pressure, you raise the boiling pt of coolant 3 degrees F. So BP with a good cap, about 260 degrees F, with no pressure, ~220 F Have your rad cap checked yearly before the hot weather. A bad cap can also cause bad heater performance in winter.
2. Thermostat- Sometimes, not often, a thermostat can fail in the closed position. This doesn't happen often, but if it does, your vehicle will overheat quickly. They usually fail wide open. Thermostats can also get lazy and open slowly which isn't good either. Never run a vehicle without a thermostat. The coolant needs to travel slow enough to pick up engine heat. A 160 degree thermostat is the lowest recommended for most vehicles. Factory is usually 195 degrees F. Change thermostat every 10 years or when you do a flush and hose change.
3. Top rad hose- The coolant is at the highest temperature and pressure as it enters the top rad hose. They usually fail where they connect to the rad and there is a lot of restriction. Replace if they get soft or bulge out. Bottom hoses rarely fail but should be replaced along with the heater hoses periodically.
4. Heater T fittings- Where the hot coolant goes into the heater, the fitting or the hose can fail. Check and replace as required.
5. Radiators/ Water pumps- If the rad gets plugged up from dirty coolant not changed regularly-overheat. If the water pump seals fail or fan belt slips-overheat. Heater cores can also fail, and if lucky you will be warned by the sweet smell of anti freeze in the passenger compartment. Service as necessary.
6. Fans- If the fan fails, or the relays, or differential thermostat, you will overheat at slow speeds. You will notice engine temps rising fast if you are in slow traffic.
As the weather gets hotter and we travel with loaded cars, pulling trailers and having AC on to keep from going crazy in the heat, you increase your chances of overheating. If your car overheats, pull over, open the hood and let it cool down. Do not open the rad cap with engine overheated, severe burns can result, and never pour cold water in an overheated engine. Doing so can crack the block or warp aluminum heads.
If you are stuck in traffic and engine temp rises, shut off AC, open all windows, and set heater on defrost position, max fan. The heater core will act like an extra rad and help keep the engine from overheating.
High performance engines require more cooling capacity( bigger rads, higher volume pumps). Running smaller pulleys can add to thermal loading and I don't recommend it, for the little extra horsepower you may get.
Check your cooling system before you travel, it's all good until it isn't. Stay cool!