Quote:
Originally Posted by ps2fixer
That doesn't match my experience driving with no cooling fan at all. Ideling will overheat the engine, moving slowly like 15-25mph it stabilizes fairly well, and 35mph+ it cools and never gets any hotter than with the fan. I'd dare to say you have a dirty radiator, restricted coolant flow, or the vehicle is of a poor design.
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You sound like you're talking about flat ground. Cruising along at highway speeds on flat ground only needs about 20hp or about 15kW of power in most vehicles, give or take. At 15% efficiency that's outputting only about 85kW of heat, half of which goes out the exhaust, not the radiator. But that same engine will have to produce 5 to 10 times that power, and therefor 5 to 10 times the heat, going up a steep mountain pass. That could be some 400kW of heat output or more!
Every vehicle design is different. Granted the engine on my car didn't immediately overheat going up that 7% grade at full throttle going as fast as the car possibly could (1984 VW Golf diesel), but the gauge did slowly keep getting higher and higher until it was nearly at the red. The cooling system was perfectly fine with new pump, thermostat and coolant and actually I had more problems with the engine running too cool than running too hot.
Many of the commercial vehicle's I've driven will audibly engage the fan on hill climbs too even going as fast as 45mph or better.
Of course keep in mind too that the fan is aided by the movement of the vehicle. So you get even more air flow when the fan engages.
I find the statement of a Nascar vehicle needing a radiator the size of a beer can very hard to believe although reading
THIS it looks like they do reduce the size of the grill for aerodynamics reasons but end up with coolant running temperatures of 280°-290°F (and oil temps of 320°-330°) as a result!