Thread: Viscous coupling and thermo fan replacement

Explain static pressure please?

I'm struggling to apply the formal definition of static pressure to a fan:

Are you talking about the relative air pressures in front of, and behind, the radiator?

Fans are rated in CFM and static pressure, the airflow is rated with zero resistance applied to the fan (nothing in front of it). Static pressure comes into play when you place obstacles in front of the fan as the CFM is reduced eg. Heat sinks, radiators, etc.

You'd need a reference to compare against however if fan A was rated at 92.3 M3/h and 1.68 mm h2o static pressure and fan B was rated at 111.3 m3/h and 1.43 mm h2o static pressure fan A would be more effective as when the resistance of a radiator was placed in front of the fan it's CFM would actually be higher. You'd also need to know what kind of flow restrictions the radiator, condenser and intercooler would place on the fan.....

It gets very involved if you get right into it. However knowing the CFM and static pressure of a fan lets you compare to fans easier.

http://www.asi.ksu.edu/DesktopModule...ocumentID=5131

A bit of a read if you want something more technical / correct.....

Yes I'll need to do some reading to get my head around that.

If a fan is meant for radiator application it will be fine. All I'm trying to say is just cause two fans can flow the same they're not necessarily the same.

OK, I think I have a grip on the static pressure issue.

What about the shroud : can I mount the fan housing up against the inside of the standard shroud to make sure the pull air-flow is correct?

Or should I rather look for a pair of fans with their own shroud that can be modified to fit nicely around the radiator? (Ford Falcon or similar as per other threads)?

I'll be using a VW Golf thermo switch (because it's cheap and goes on and off at the right temps), in a mild steel pipe in one of the radiator hoses.
(I've used this method previously and successfully on a Nissan VG30E)

Which hose is best on the Rover V8? Top or bottom? I assume the hose between the mechanical thermostat and the radiator?

I will then run a +ve to the switch, then from the switch to a relay, and feed the two fans from the switched side of the relay. When the thermo switch comes on, it will close the relay and the fans will run.

Anybody see any issues there?