Coolant flow

72bluNblu said
"Packing up", as you put it, is a rare problem usually only associated with flat plate style shrouds that come on the cheapest of cheap aftermarket electric fans. If a fan's shroud has flaps, that should be a dead giveaway is wasn't actually designed to flow air and that it was just slapped together and band-aided. There are a lot of aftermarket electric fans and shrouds that have no business on cars- their fan CFM ratings are too low, and their shrouds are simply a way to mount their cheap fans, not actually flow air.

I did read what you wrote, and you said "good mechanical fan" was necessary. It's not, a good electric fan and shroud work great. Maybe that's not what you meant, but that is in fact what you said.

You should care, because getting it wrong can mean cavitation in the water pump. The cars that had 1.3:1 and 1.4:1 pulley ratios had pumps with fewer blades. The reason is the RPM of the pump and cavitation, not the amount of water it's pumping. Running a high flow pump is good and the idea you can flow water too fast is silly, I agree. But, you still have to consider the RPM of the pump and how it's being driven. A 1:1 pulley ratio with a high flow water pump is one solution, but if your pulley ratio is 1.4:1 you need to account for that too. Some of the pumps are designed differently now, but the factory was looking at the pumps driven speed and adjusting the blades accordingly.

The majority of your points are right on and I agree, but you leave science behind on this point and just go with what you're personally familiar with.

The 180° temp thing is just left over from your drag racing background. Not every car/engine that gets discussed on this board is used the same way. If 180° was some magic number, the modern OEM cars would use it too. Yes, modern cars have to tune for a lot of other things too, but they all make higher hp/cube outputs than these cars ever did stock- they're more powerful and efficient. Sure, the engines discussed here usually aren't stock and don't have smog to worry about, but most of them also don't have nearly the control over their fuel delivery and ignition systems either. Literally no modern cars spec their water temps to be 180°, and a couple dozen degrees of coolant temperature aren't going to hammer your cylinder and exhaust temps so badly that you couldn't deal with meeting the smog and efficiency requirements. Modern OEM's could easily spec a 180° water temp if it made the most power or was the most efficient. They don't, and it's not because they don't know what they're doing.

If you were familiar with other kinds of racing, you'd know that pretty much only drag racing cars keep their engine temps under 180°. There are much crazier and exotic engine builds out there than make gobs of power for a lot longer than drag engines do and do it with much higher coolant temperatures. For a street car, it's not necessary or often even practical to keep the coolant temps between 160° and 180°.

Yeah, that's just BS. Modern cars pretty much ALL run electric fans, and some of them make more horsepower than dirt track cars too. Using a race car as an example is also usually a bad idea, since there are typically specific rules and regulations that require certain things and not others. And pretty much every automotive racing environment is highly specialized, and requires things that don't make sense on a street car. Why dirt track cars run mechanical fans instead of electric I don't know, but it's absolutely not because electric fans aren't capable of cooling those cars.

I said this in another post but the application can be what determines what fan does the best job.

The horsepower rating of the engine is not necessarily a good yardstick for what fan is needed. For example: You have an engine that makes 700 hp and you use that power for an occasional burst of acceleration then spend the rest of the time using 20 hp to cruise down the road or idling at a stop sign. Compare that to an engine that makes 400 horsepower that is being raced in a circle or on a road course that spends most of it's time making close to that 400 horsepower. The cooling needs of the two examples can be very different.

I think a better way to think of how much heat you need to extract is horsepower over time.

Electric fans have come a long way. They are more efficient than ever. But they move the same air if the motor is idling or at full load high rpm. Mechanical fans while not load sensitive are rpm sensitive. They move more air with increased rpm. They also have a power source that can power a large aggressive pitched fan blade. Try putting your hand in front of a radiator with an aggressive fan spinning 6000 rpm inside a good shroud. It moves alot of air.

Something to think about and I don't know the answer too. An aggressive pitched 4 blade mechanical fan can use 7 Hp. Assuming the fan efficiency was close to equal (maybe it isn't) how big would the motor on an electric fan need to be to move the same cfm that the mechanical fan is moving at 6000 rpm?