19z28camaro02

At what speed (MPH) does it become pointless for you to have your high speed fans on?

MikeGyver

At the speed that your car can naturally cool itself.

Z28SORR

There is no specific number it varies depending on conditions. In 4th gear, below 90*, with AC off, I would think somewhere in the range of 40 to 45mph should get you enough air flow so that you wouldn't need the fans. With the AC on the fans come on automatically. If it warmer or your at high DA settings, etc. you may have to be going faster.

Injuneer

It's going to depend on more than the velocity of the car, since the radiator is not directly in the path of the oncoming air. The air dam and the ductwork leading to the radiator control the air flow in a bottom feeder. You would have to know the air pressure at the air dam, how it changes with velocity of the car, the amount of clearance between the dam and the road, how well sealed the ducting is.

In retrospect, the first answer you got is the correct answer. Disable the fans, drive at various speeds until the coolant temp stabilizes, and record the results.

WS6 TA

In theory it could be answered with math if you could gather enough numbers, but you'd have to have specific air flow numbers, fin density and design, how much the stock fans block, so on and so forth...

Just test it, but usually it ends up in the 25mph range...

JP95ZM6

Above answers are all more or less correct, but I'll explain a little differently. CRFM airflow is driven by two components: ram air, and fan power. The car will have a ram airflow curve vs MPH, and one for fan on. Total flow at any speed depends on the balance between the two. Even at high speeds, say 100 mph+, there is a little bit of contribution from powering the fans instead of letting them freewheel, but it's not much for most cars.

Then, there is the operating condition: heat rejection and air temperature combined determine how much airflow is needed for a given operating point. Pretty much any car will still benefit from fans at highway speeds, in terms of getting extra airflow, but it's not needed for most vehicles to keep temperatures under control. Climb a hill in the desert, like the highway grade in Baker, CA, and it's a different story.

It's pointless to have the fans on at any speed/load/air temperature where you can maintain coolant temperature, but the speed at which that happens depends upon the specific load case in question. Uphill, tailwind, hot day, A/C on, all mean fans help more, and at higher speeds. Many cars will need fans on, even at highway cruise speeds, under such conditions. This is becoming more of a trend, as front end openings get smaller and smaller to help reduce the aerodynamic drag penalty from excess front end airflow on the EPA tests, where having JUST enough airflow with the fans off gives best fuel economy.

460 Maverick

Just ran into this. Get on the highway on a hot day, disable the fans and drive it while watching the engine temperature. You should be able to gather some good information and answer the question.

Al 95 Z28

WS6 TA

Yea, but whatever point you find will change with different air temperature and even just slightly different power levels. Tune (especially timing) and exhaust will also make a big difference.

460 Maverick

So tell us what you got when you calculated it.

Al 95 Z28

WS6 TA

the math exists, but it's not worth really doing it, same variables as with trying to test it empirically but add in odd stuff like fan blade pitch, radiator fin density and thickness...