[Jack21]

Modern engines, and their components are designed to run hot to vaporize fuel, burn fuel, operate at optimum clearances, and burn off engine contaminants. Typically, this is in the 180 - 205 deg. (f) range.

A 180 deg thermostat is full open at 180 deg. This sets the minimum temp your engine should run at. Freeway cruising, your engine temp should sit on 180 and the cooling fan should not come on.

The fan sensor turns on at 205 deg, and off at 180 deg. With the engine idling, the fan should cycle on and off as the coolant temp rises to 205 (fan on) and falls to 180 (fan off).

Putting a manual override switch in the fan circuit will give you a margin of safety in keeping the coolant closer to a constant 180 deg.

If engine temp climbs over 205 deg. and the fan stays on constantly, coolant temp will reach an equilibrium temp based on the capicity of the cooling system to dissipate heat. Obviously, the coolant temp should never exceed its boiling temp.

We use two methods of preventing boiling of the coolant. Make the cooling system more efficient at removing heat, and raising the boiling temperature of the coolant.

Bigger radiator, bigger fan, better shrouding to improve airflow through the radiator, and coolant wetter all make the cooling system more efficient.

Using a higher boiling temperature coolant (e.g. propylene glycol) and/or raising the operating pressure of the cooling system (higher psi rated radiator cap) will keep the coolant in liquid form.

Coolant expands when it gets hot, and contracts when it cools. With no airspace in the cooling system, hot coolant needs a place to go. Your garage floor is one, a coolant overflow bottle is another. For about $10 - $15, you can get a coolant recovery kit for hot coolant to reside in, and return to the radiator when cool.

Hope this was helpful.