Thermo Fan Benefits

[Alan 4Runner]

Hey all,

This may seem silly but as my name suggests, I have an old 4runner with the ever reliable but slower than a month of sundays 3y!! My question is this:
Will there be ANY power gained by ditching my clutch fan and whacking in a thermo fan?
I realise that the engine will rev easier when stationary but would there be any gain whatsoever when driving along?

I'm just looking at any cheap gains i can get before I begin my 7m-ge swap next year

Cheers peoples

[CrUZida]

There will be some gains as there will be no parasitic loss on the motor, however if its a decent thermo it will probably draw more power when its running than the belt driven fan.

[PlacentaJuan]

yea they draw quite a bit of curent that your alternater will need to provide by demanding it from the engine

[Draven]

"cheap gains" and swapping in a thermo are just not part of the same part of an engine's modification

[Alan 4Runner]

Thanks for the advice guys, automotive electrics aren't my strong point unfortunately..

My understanding of alternators (quite likely to be incorrect) is that they are similar to a DC electric motor with a copper wound, segmented armature only in reverse with external copper wound segments with the magnets spinning inside generating the current..

Does extra amp draw on the alternator cause it to become more resistant to turning??

If this is the case then i guess thermo's wouldn't be overly advantageous...

[CrUZida]

Yes, the more draw on the alternator, the harder it is to turn.

[brett_celicacoupe]

the power used by the thermo = Volts x current. so 30amps at 12V = 360watts.


the power has to come from the engine and due to losses the power supplied to the alternator by the engine may be as much as 20% more, not including the other current loading due to lights/fans etc.

[Shakotan_Aaron]

but the thermo should only turn on in heavy load (towing uphill) or stationary (in traffic ect). if the cooling system is in good condition the thermo (assuming its to an automatic sensor switch) shouldn't kick in while normal driving.

i have my thermo fan on a manual switch. i also recently upgraded my radiator as the old one was barely cutting it during the cooler months. i rarely actually use my thermo unless im travelling at under 40km's or stopped when the car is upto temp. even when im giving it a thrashing in the hills rarely turn it on going uphill (down hill is always off).

[CrUZida]

Turn the aircon on and you'll find thats a different story.
The thermos will need to run at sub 60kph constantly or your a/c won't be very cool.

[Bazooka]

Just bolt the "BIG BLOCK" 4Y engine into it
I prefer thermo fans over the engine driven fans especially if your offroading as you will be doing slower speeds where the thermo will outflow the engine fan. Down side is water crossings and swamping the fan but I highly recommend the SPAL fans which I have had for years without any drama and they flow really well.

[Shakotan_Aaron]

i was just saying aproximtaes, as i said i upgraded my radiator so its more efficient to start with.

[Alan 4Runner]

Well people, I went and did the swap anyway!

When the fan is running it feels about the same as when it had the old clutch fan, maybe a tiny bit slower..

Like ae71 I have just wired the fan up to a manual switch and have found that I rarely need to switch it on unless I'm battling through peak hour traffic

In my case, the loss caused by the load on the alternator is nothing compared with the constant drag on the motor from a fan which 90% of the time doesn't need to be used!!

For the sake of the $50 I spent on a relay and a second hand thermo from the wreckers I'd say the extra 30km per tank of petrol is definitely worth the effort

Cheers for your info guys