First of all, I did this on a 75 Olds that had overheating problems, but
the general technique should also work on any car. I am told you can buy
an "electric fan kit" (not necessarily for the SV-1), but here is the El
Cheapo junkyard method). You will need an electric fan (Junkyards
usually have a rack full of them, about $20 or so), a horn relay (any
automotive supply store), and either a switch or a normally OPEN thermal
sensor (you may have to experiment with the temperature, I used one that
opened at about 150 deg F). The relay is definitely necessary if you plan
on using the temp sensor, since the fan will typically draw about 10 amps.
The simple way (manual operation) is to connect one end of the fan to +12
and the other end to the switch (standard on/off type, watch the current
rating). The other terminal on the switch connects to a convenient ground
point inside the passenger compartment. The good news is that you can
activate the fan whenever you want. The bad news is that there is a
scenario where you have been driving, the air flow from the car's motion
keeping the radiator cool, you stop, the engine continues to heat the
coolant, and after a few minutes the radiator will overflow. If the
problem is bad enough, the overflow tank will overflow also. And you
don't want to turn the fan switch on when you stop, unless you're sure
you'll remember to turn it off. If you don't, well, it's a self correcting
problem- the battery will gradually drain and turn it off for you ;)
So consider "Plan B" - use a temp sensor to determine when the fan turns
on. Unfortunately, the majority of the temp sensors available (typically
to turn off attic fans in the event of a fire) are normally CLOSED, and
open when the trip temperature is reached. I found some normally closed
button type sensors at a Hamfest (that's the electronic equivalent of a
car swap meet), but only one had a useful temp range. You can probably
find a source on the 'net somewhere.
The horn relay will have three terminals - +12, "horn", and "coil".
Typically, the coil side wants to be grounded to energize the relay, but I
have seen some where ground is made through the relay housing and the coil
terminal wants to see +12v to energize. Anyway, one of the two terminals
on the temp sensor goes to the "coil" terminal, the other to either +12 or
ground (depending on what kind of relay you have). The "+12" terminal on
the relay goes of course to +12, and the "horn" terminal goes to one wire
of the fan, while the second wire of the fan goes to ground. Which wire
to which on the fan ? Depends on which way you want the fan to rotate and
where you mount it. I prefered the "push air through the radiator" mode
on the front of the radiator.
Now the only issue is where to mount the temp sensor. If you simply want
to detect engine compartment temp, you might want a lower temp setting
(maybe 130 deg or so). If you want to mount it directly on the radiator
housing, use a higher temperature. I mounted mine with high temperature
RTV on the overflow line out of the radiator. I figured the radiator
would start to overflow when the coolant was getting too hot (not exactly
rocket science, but effective).
Obviously, this only one path to a solution. Several others have posted
their ideas (insulating tape on exhaust manifold, bigger radiator, etc.).
There are a million stories in the "Naked City", this is but one...
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I am Pentium of Borg, precision is futile,
you will be approximated...
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