www.RX7fb.com

Ok here's my take on it, and correct me if I'm wrong. The radiator and fan are there to prevent coolant temp in the engine going above a critical temperature. So you measure the temp at the hottest point, yeah? If its too hot at the hottest point you have a problem. If the temp is good at the hottest point everything is fine! Just because the water exiting the rad is cool doesnt mean you aren't overheating you're engine!
Of course im no expert, and I'm not knocking, just thinking out loud..

I agree that to take a reading for a temp gauge we would need to take it from the hottest point but perhaps not for a sensor for a E-fan. The coolant coming out of the engine is always going to be hot, it's come straight out of the water jacket. The fan doesn't need to know how hot this coolant is at this point because it's pre-radiator and the rad should take care of it.... if it does take care of it, then the fan is out of the equation.
Coolant exiting the rad via the bottom hose should be what, 10 deg below the coolant going into the rad? This is where the e-fan sensor needs to get it's signal from. If the temp of the coolant going into the engine is lower than the temp coming out then the rad is doing it's job but if not and the coolant hasn't been cooled, or cooled enough, and then goes back into the engine and around the water jacket again then we have a problem. So if the fan is detecting the temp at this point and the temp is cool enough, the fan doesn't kick in but if this temp rises above a set point, the fan kicks in.

The rad controls the heat and the fan is only there to supplement the rad.... theoretically, we could drive 100 miles without a fan fitted to the car as long as we kept moving at a decent speed and the rad was in good order and big enough to do the job.
By taking the reading from the top hose we are sending a signal to the fan maybe telling it to come on even before the rad has had a chance to do its job. The stat opens at engine operating temperature and we don't want the fan to trigger at that point or else it would be running constantly but if we set it higher the engine actually has to overheat slightly before the fan kicks in.

I'm not saying I'm right here guys, I'm just trying to work out why some e-fans use the top hose and some use the lower hose.... the manufacturer of my fan controller spec'd the bottom hose as the sensor point but others suggest the top one or into the rad core. The bottom hose seems to make more sense to me but I'm happy to be convinced otherwise

What if the coolant at the top hose is too hot but the rad on its own cools it enough for the efan with sensor in bottom hose not to kick in ?
What would happen if you had poor circulation ?
I think if the hottest point controls the fan you cant go wrong, saying that if you look at a more modern car with factory fitted e fan the switch for the fan seems to be halfway up the rad so we are all wrong
As I said before it really doesn't matter, an e fan is a great idea no matter where it takes its temp reading from.

Yeah maybe its six of one half dozen of the other.

Dont mean to be argumentative though, but e-fan usually isnt as effective as good old clutch fan either. If your cooling system was marginal with a working clutch fan, an e-fan will probably make things worse, just saying its something to consider for anyone who reads this that it isnt actually a step up in cooling power, just a good way of losing some friction loss at the engine.

myatt1972 wrote:What if the coolant at the top hose is too hot but the rad on its own cools it enough for the efan with sensor in bottom hose not to kick in ?

that's my point.... if the rad cools it enough on it's own, why would the fan need to kick in?

myatt1972 wrote:What would happen if you had poor circulation ?

then you're probably going to overheat regardless of where the fan sensor is located

myatt1972 wrote: I think if the hottest point controls the fan you cant go wrong, saying that if you look at a more modern car with factory fitted e fan the switch for the fan seems to be halfway up the rad so we are all wrong

that's probably the best place for it

myatt1972 wrote: an e fan is a great idea no matter where it takes its temp reading from.

Yep

I couldn´t follow all your arguments exactly. But i found out first the hysteresis of the switch point are very important. And second two different position of the
two sensor.
As ian say outlet engine the first switch point will start the vent in low condition. The second switch point (top) on the engine inlet start the vent to high level if the temperature reach a higher point.

Waterflow is from front to the rear in the engine. Oilflow is from rear to the front. Engine cooling with oil, water and important too waste heat.

ou can see the parts i take for a long time (100000km) in for tests in the 90ties.

Forgot to say the BMW 323 i Ventilatorrad is on the exactly same position as the visco ventilatorrad.
Thomas

^ Just checking to see if ive got this straight - the fan runs of the 1st (cold) switch, and is overridden by the 2nd (hot) switch if temps go north or the coolant level drops for whatever reason?

Also, just to reiterate, an electric fan isnt an upgrade over the standard clutch fan. Not that it would matter much in an English climate or with a healthy system, just sayin.
typed "electric vs clutch fan" into the google machine and the 1st thing that came up was one of Mr Cake's helpful articles. I wouldn't take everything he says for gospel, at the end of the day he's pretty much just an enthusiast like the rest of us, but he is cluey and a good read.
http://www.aaroncake.net/rx-7/efanmyth.htm

I think this is a debatable comment .... " For the most part, electric fans are not recommended as an upgrade unless you have a very specific reason to do so"

Nearly all modern car manufacturers these days install electric fans as OEM instead of viscous fans... when they put millions of pounds into vehicle design and development, presumably they come up with the most efficient components.

I'd take an e-fan over a viscous fan any day.

Mainly on east-west arrangements and to supplement belt fans on north-south untill recent years though...
Yeah it is debatable, but when i was originally looking into it, it seemed a lot of aussie guys actually went back to clutch fans when their e fans couldnt keep up. It was on the internet so it must be legit...