There’s the belief among some that the engine coolant can go through the radiator too fast and not have enough time to dissipate its heat or that it’s passing through the engine too fast to pick the heat up. This belief probably originated via the observation that removing the thermostat can cause the engine to boil over faster. Adding a baffle into the thermostat housing to restrict coolant flow will then make boiling over less prominent. (The reality here is that a flow restriction at the coolant’s exit from the engine will raise the pressure within the engine which raises the boiling point of the fluid inside the engine cooling jacket.)
Another method of slowing the coolant flow that people use is a multiple pass radiator. They see it as a dual benefit of slowing the flow and providing the additional cooling of more radiator surface. It does decrease the radiator outlet temperature, but the temperature within the engine will actually go up because the fluid spends more time there as well.
Regardless of the fluid used, it is always easier to transfer heat between liquid and metal than it is between metal and air. The system’s heat transfer limit is at the radiator. The radiator is more efficient with a greater temperature difference between the metal and the air. If the air temperature is 90 and the radiator temperature is 95, not much heat will transfer compared to an air temperature of 90 and a radiator temperature of 250. (I’m using extreme temp numbers here just to make the point.) This means that the cooler end of a multiple pass radiator is less efficient than the hotter end.
A cooling system works best when there is a fast coolant flow and the radiator temperature remains high because it can shed heat to the atmosphere better. Water-based antifreeze puts a limit on the coolant flow rate because the pump can only turn so fast before it cavitates. Basically, the low pressure side of the pump has a lower boiling point and the fluid will vaporize; the pump can’t move a vapor.
Evans Coolant solves the boiling point problem allowing aggressive pump speeds and eliminating the need for engine coolant exit restrictors.
Tech Tip: Hot Weather
It's above 90°F the A/C is on, temp gauge has moved from normal to almost too hot what can be done? Most cooling systems today have a heater core built in for defrosting the windshield, cold weather heat or defogging in rainy weather. Most people do not know that the heater circuit is on all the time in most applications. Hot coolant is circulating through the heater core under the dash, this coolant does not go through the radiator to dissipate heat and help cool the engine. The heater circuit is a radiator bypass loop, some system have a control valve that shuts off the coolant flow when heat is not condition to help lower the temperature why not be more comfortable and let the radiator do it's job. To remedy this problem a simple manual valve can be installed in the heater feed line or a 1/4" restriction can be fabricated and put in the hose. Before doing this make sure the hose you select only feeds the heater core. By shutting off or restricting this circuit it redirects the coolant flow to the radiator where the operating temperature can be decreased by 10 to 20 degrees.
