Quote:
Originally Posted by Old Mechanic
The isssue with winter engine cooling is as temperatures get lower the difference in temperature between the coolant leaving the engine and the coolant entering the engine, after going through the radiator, can get fairly large. In some cases over 100 degrees difference is severe conditions, and even higher in very cold areas. In very extreme conditions the heater core can provide all necessary cooling in some cases.
Blocking the air flow over the radiator lowers that temperature difference to a point that more resembles the summer difference, which might be as low (a difference) as 30 degrees.
The colder your coolant is when it enters the engine, the more heat loss you suffer to the coolant and the lower efficiency of your engine. In cooling systems with electric fans, you know you have overdone the blocking when the fan starts running a lot more than it did before your mod, and you are spending a lot of energy running that fan.
I am also an advocate of cooling systems that use the bypass circuit to control the incoming temperature of the coolant automatically to maintain the highest practical inlet temperature, something current systems (with few exceptions) do not do, which is the main reason for blocking airflow to the radiator.
regards
Mech
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Adding to what Mech said above.
Another reason to keep water velocity high through the engine, is protecting the cylinder heads.
Why?
When you pour the coals to the engine by stepping on the gas hard, the exhaust port in the engine gets really hot. Much hotter than the water temperature itself.
In fact the water temp can go high enough that localized boiling of the water occurs, especially if the water velocity in the area is too low.
The high water velocity scrubs the boiled water bubbles from the jacket walls and keeps the exhaust port jacket from over-heating.
Best the keep the water velocity more towards "normal".
I also notice that when I do repetitive EOC pulse and glide, the engine has a tendency to heat up, especially on already hot days.
This is because I use about 1/2 throttle at low rpm's to take off, and then shut off the injectors, which stops the motor and it retains the heat from the high take off. After doing this repeatedly, the heat builds up over time, because when coasting, the engine does not cool much since the water pump is not circulating fluid.
Jim.