[gjz30075]

Hi all,
I have a problem of trying to get my electric fan to shut off. I'm running a 331 with a nice aluminum radiator with a Spal 16" fan. Kicks on when its supposed to but rarely turns off. My temp gauge is reading normal and per my laser temp gun, all parts of the cooling system are fairly normal,like 185-195, except where the sending unit is located.

As you can see, I'm running heater pipes instead of hoses; they're off some Ford car but don't know what. I liked its configuration better than the late model Mustang type.

Anyway, the area of the pipe where the sending unit sits is a good 15 degrees hotter than anywhere else, hence, it doesn't cool down enough to turn off the fan. The sending unit is for 200 degrees on, 185 off.

So, is there a sending unit that exists (Spal maybe) that I can use for both my stock guage ('66) and my fan trigger so I can install it in the stock location in the manifold? Or, is there a better place to put this sending unit, while keeping my stock one, for a more accurate temp reading?

Unfortunately, I have only the one hole in the manifold water area for a sending unit. I was thinking of drilling another? Bad idea maybe?

What do you think?
Thanks

 

[Stroked66]

Stock sending units don't have the same ohm resistance as the modern senders the Spal's are made to use. So you cant use the same sender for both your stock gauge and the fan (But you can use a single modern sender for both the Spal and an aftermarket gauge like Autometer)

That said, a few options come to mind;

1). Switch sending unit locations. Place stock sender where spal sender is and vice versa. Your stock gauge will read high, but you'll know you're within proper limits.

2). Get a higher rated on/off switch to compensate for the difference between heater bypass and true manifold temp

3). Swap out your pre-set on/off switch, with a standard late model sender and use Spals programmable controller. That way you can set the on/off wherever you like.

 

[bimmer95]

I picked the same location that BMW uses for their fan switches (actually used a BMW switch too), the cool side of the radiator. It actually makes a lot more sense when you think about what the fan is supposed to be doing, increasing the air flow through the radiator only when the existing air flow is insufficient to cool the engine coolant. If you're driving, the coolant is below 176F by the time it passes through the radiator, but when you're sitting still, the coolant stays much hotter causing the fan to come on.

The switch that I used has dual temp outputs, so I also used a BMW fan resistor and a pair of Bosch relays to make the fan dual speed as well. If the coolant reaches 176F, the fan turns on at a low speed, if that doesn't work and the temp hits 190F, the fan is kicked up to full speed.

 

[gjz30075]

Thanks guys, great ideas. Stroked, I like the idea of the programmable controller. I've read alot here about it and it seems fragile but Spal's pdf file on it seems to address some of the normal problems one has with it.

I also like the idea of relocating the sending unit. "The cooler side of the radiator" I'm presuming is the bottom tank. Bimmer, any pics of yours?

 

[bimmer95]

I don't have a good picture of mine. It's not exactly where I'd want it anyway, my fabricator welded the bung in all the way at the top of the tank and the wires are more obvious than I'd like them to be. The lower half of the tank on the outlet side would be ideal.