Cooling fan horsepower

[vkh]

So in an episode of engine masters they tested some common mechanical cooling fans to see how much horsepower they actually use. They had a mild 350 that made 349 hp and 406.9 ftlb. They were winding it out to around 5500 rpm. They had a radiator and shroud, all the fans were the same diameter and had 6 blades.

The thermal clutch fan ate 14 hp and 6.9 ftlb.
The plastic flex fan ate 23.9 hp and 18.6 ftlb.
The aluminum fixed fan (shallow blade angles) ate 20.3 hp and 12 ftlb.
The old school steel fixed fan ate 30.4 hp and 18.6 ftlb.
Without shroud the steel fan ate 22.3 hp and 17.9 ftlb.

These were the largest point differences but seeing the graphs but it does follow a steady trend. Worth noting too that the dyno room was quite cool, I think it's safe to say the thermo fan would eat more power on an average summer day.

So I was quite surprised by how much power mechanical fans eat, I was always a little skeptical about how much benefit electric fans bring but now I'm convinced.

For a power estimate for an electric fan a 30 amp fan uses about 360 Watts at 12 volts. Giving the alternator a 75% efficiency it would use 480 Watts mechanical, which is .64 horsepower.

Thought you guys might find it interesting.

 

[Camar068]

good info, thanks. Yesterday, I was actually wondering the same thing about the power steering pump.

 

[1987 GMC Jimmy]

I agree that the real world aspect for the thermal clutch fan is diminished by being on an exposed engine in a cool room, but I'd think the factor that comes into play more is engine bay temperature as opposed to ambient temperature. I say that because even though the fan is gonna suck in some cooler air, it's also sucking in air that's passing over boiling hot coolant and boiling hot refrigerant, transmission fluid, and engine oil in some cases. Plus, the engine and exhaust are belting out all kinds of heat. I could be wrong, but I'd think unless you lived in a much cooler place, that the engine bay temperature is what's gonna affect it more.

 

[Honky Kong jr]

X2 on real world thermal fan when fully engaged it will more then likely rival the highest parasitic hp loss shown above. Electric fans are 1 of the cheapest hp gainers. I have a collection of crown Vic fans all but 4000cfm on high I get them from a local pick a part for 10 buck. Helpful tip when fan searching carry a drill battery with you to test.

 

[vkh]

I agree that the real world aspect for the thermal clutch fan is diminished by being on an exposed engine in a cool room, but I'd think the factor that comes to play more is engine bay temperature as opposed to ambient temperature in the reality. I say that because even though the fan is gonna suck in some cooler air, it's also sucking in air that's passing over boiling hot coolant and boiling hot refrigerant, transmission fluid, and engine oil in some cases. I could be wrong, but I'd think unless you lived in a much cooler place, that the engine bay temperature is what's gonna affect it more.

I agree, under the hood temps are more of a decider than outdoor. I was mainly thinking a summer day would probably be the average use case for most squares. Though since the fan is just behind the radiator it always has new air circulating instead of stewing in a placid spot. If we consider the engine to produce about the same heat at a given load regardless (within a reasonable range) of outside temp, that is to say the engine is creating about the same amount of thermal energy regardless of air temp. Then considering the Cp (enthalpy) of air is almost unchanging with temperature and we pretend that our thermal energy is being transferred perfectly into the air it will increase the temperature of the air flowing through the radiator by the same amount regardless of the airs initial temperature. That is to say air that started at 20 would go up to 140 while air at 80 would go up to 200 past the radiator. If we look at it very simply it's a fair estimate to say the air past the radiator would be proportional to the outside temp. But of course it's not quite that simple since we can't magically transfer the heat to the air, we instead bring the water and air closer to an equilibrium so the closer the water and air temps are the less efficient our heat transfer is. Well, that was a rather rambly way of saying the outside air temp will effect the after radiator air temp directly.

 

[Honky Kong jr]

What he said. It could also be dumbed down into when it's hot the fan will be robbing more hp from the engine...lol nice dissertation on thermal dynamics tho.

 

[HotRodPC]

This is exactly why auto makers have gone to Electric Fans. When an accessory takes away horsepower it also affects mpg too. Anytime any accessory robs horsepower from getting to the drive wheels and to the ground to propel the vehicle, it's called, "Parasitic Horsepower Loss".

Had anyone ever noticed race cars like to run Electric motors to even operate the Water Pump and/or Alternator??? All of those things on the front of the engine will take something. Even an AIR (Air Injection Reactor) pump aka Smog Pump will rob 2-3 horsepower from getting to the ground.

 

[Honky Kong jr]

Under driving is another way of cutting parasitic loss as well but also can damage accessories i.e. Ax compressor,alt and ps pump. But also extra electrical load can tax alternators as well if not sized properly.

 

[vkh]

What he said. It could also be dumbed down into when it's hot the fan will be robbing more hp from the engine...lol nice dissertation on thermal dynamics tho.

Lol, better put some of this fancy learnen I'm paying for to use!

 

[1987 GMC Jimmy]

Oh my. If I told you that I ever did well with thermodynamics/thermochemistry, I'd be lying for sure. Your explanation definitely triggered memories of sleepless nights and worrying about passing homeworks and tests over the course of two years.

 

[Honky Kong jr]

Just another example of the younger generation over complicating things. Lol

 

[1987 GMC Jimmy]

I agree with you 100%, but I can't plead total innocence. I'm only a year older than vkh.

 

[vkh]

Just wait 20 years when we start taking over serious jobs, then we'll really have things nice and complicated, lol.

 

[1987 GMC Jimmy]

*Insert derogatory comment towards younger generation and/or the federal government*

 

[HotRodPC]

*Insert derogatory comment towards younger generation and/or the federal government*

I agree, it's the Feds who turned the millennials into *******. Hate to say that, but it's a sad fact. There's still a few good kids out there but most are not. If most kids today had to make it on their own, they'd fall flat on their face. And it only gets worse with each generation. Soon it'll be EVERYONE will live off gubment assistance of some sort because of the way our kids have been allowed to be raised. In short, it's all about discipline and education. Kids don't get either the last several years. Then we wonder why Middle Eastern countries will take over this country in the next 2 or 3 generations.