A question about Thermatic fans

[aarc240]

Sure did read that bit and you're right. btw, I wasn't having a go at you.

The 3 core radiator is no guarantee of improved cooling (which is why Ford stuffed the Galaxie radiator into all RPO83 XA GT's for the bigger surface area rather than adding another core layer).

Curious that you are having issues with a rotary too! I've finally licked the problems we were having with the young fella's RX7 series 2 13B turbo. Wound up scrapping the PO fitted heavy duty radiator (4 core!!!!) and used a two core aluminium cross flow with two 12" electric fans in a custom shroud.

Reckon the nose came up half an inch!

You can't draw a parallel on the input power to a stock fan with an electric - a lot of the loss is parasitic drag because of the (necessary) belt tension.

To get meaningful figures you have to look at the air flow rate at the speed the fan is going to operate at.

In the case of an engine driven fan it slows down just when you don't want it to - at low speeds in traffic!

At that point most engine driven fans flow cosiderably less air than a suitably sized electric which doesn't care what speed the engine is doing.

[440k]

Hehe no probs. That's what exchange of ideas is about. Would be a boring place if we agreed on everything.

Well, 3 core may not guarantee much, but it worked a treat in the Datto. Even rallying through the forests north of Mackay in summer had no effect on the temp gauge - as long as the airflow was kept up.

You sure can't draw a parallel between stock fan and a thermo in terms of power consumption - my point was that 17hp vs 200w (my guesstimate) means that the engine driven fan is drawing 60 times the power of a thermo fan. Even with the horrendous losses of the vee belt (the same belt that drives the alternator, btw) you still have more air movement with an engine driven fan.

You're right about the engine speed though. You won't have as much airflow at idle (where you need it) as you would at high RPM. You'd look a bit silly sitting at the lights at 5000RPM just to keep the engine cool.

This is my first experience with rotaries, so I'm on a learning curve. I'm inclined to believe that the radiator is probably past its use by date, and am considering upgrading with a nice alloy unit. The single thermo fan sits a fair distance from the radiator, so it cetrainly isn't getting optimum cooling. I'm going to try and fit asecond unit in there, but it will mean totally rebuilding the mounts.

I have many other issues to sort out before the cooling system needs a look into. If I find that it's still running hot on open high speed stuff, then I'll certainly take the plunge.

[g72s20]

hey Jim, curious if the electric fan helped with your motor revving,

Ive read that it does(because of the less drag)--what do you think?

Not an easy one to answer. I didn't register any appreciable difference. The car was not overheating before the change, and all indications are things remained exactly the same, always within a needle width of the 80'C mark on the gauge regardless of open road or traffic. Remember it's on club rego so I don't get out a lot in it either. Even after the Dynotune the only appreciable difference is it's crisper/smoother and uses less fuel.

Art, I meant a 270'(of arc) gauge as opposed to the 90' arc of indication currently fitted. Same temperature range though. Effectively a greater resolution (more sensitivity) of the same temperature range, so variations in temp are more obvious by being shown over a wider arc on the gauge.

The fan fitted is almost the same width as the radiator. They're a bit taller than they are wide.