Discussion
Dave
The short answer is that, for given conditions and assuming that the temp gauge is accurate, the cooling system is dispersing heat at idle/slow speed more efficiently than at higher speeds when the engine is generating more heat.
The long answer is that two things keep engine temperature under control: the fuel charge and the cooling system. The radiator size, air throughput, coolant flow rate and quantity of coolant in the system determine the ability of the system to extract and lose heat. The effect of the fuel charge is a balancing act because as more fuel comes in it has a higher cooling effect but also produces more heat in the burn.
The cooling system depends on the difference between the engine and radiator temperatures to lose heat. As long as rad temperature is below engine temperature by a sufficient margin then everything is moving in the right direction. At idle and slow speeds in a good set up fans will replicate forward movement and this will keep things at the right temperature. At higher speeds and fuel burn the heat output goes up, even though airflow increases more demand is placed on the cooling system and temperatures can rise.
For a road going vehicle the design of the cooling system is a balance between a number of conditions. Cooling systems on race vehicles generally rely heavily on air throughput and this is why they can only spend so much time on grid with engines running.
Two more points worth mentioning; denser air makes for good cooling and lower temperature, altitude or humidity will make air denser. Denser air also allows a greater fuel charge on the induction cycle.
Generally bear in mind just it's as important not to overheat an engine it’s important not to overcool it. Petrol has to evaporate properly when injected and overcooling can mislead your ECU.
Hope that’s useful.
A.
The short answer is that, for given conditions and assuming that the temp gauge is accurate, the cooling system is dispersing heat at idle/slow speed more efficiently than at higher speeds when the engine is generating more heat.
The long answer is that two things keep engine temperature under control: the fuel charge and the cooling system. The radiator size, air throughput, coolant flow rate and quantity of coolant in the system determine the ability of the system to extract and lose heat. The effect of the fuel charge is a balancing act because as more fuel comes in it has a higher cooling effect but also produces more heat in the burn.
The cooling system depends on the difference between the engine and radiator temperatures to lose heat. As long as rad temperature is below engine temperature by a sufficient margin then everything is moving in the right direction. At idle and slow speeds in a good set up fans will replicate forward movement and this will keep things at the right temperature. At higher speeds and fuel burn the heat output goes up, even though airflow increases more demand is placed on the cooling system and temperatures can rise.
For a road going vehicle the design of the cooling system is a balance between a number of conditions. Cooling systems on race vehicles generally rely heavily on air throughput and this is why they can only spend so much time on grid with engines running.
Two more points worth mentioning; denser air makes for good cooling and lower temperature, altitude or humidity will make air denser. Denser air also allows a greater fuel charge on the induction cycle.
Generally bear in mind just it's as important not to overheat an engine it’s important not to overcool it. Petrol has to evaporate properly when injected and overcooling can mislead your ECU.
Hope that’s useful.
A.
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