The problem with sticking a probe between the fins of the radiator is as soon as the fan comes on, the air rushing past sensors will cool it far below the temp of the coolant inside the radiator.
If I were trying to make something like this work, I think I would put the probe somewhere that the fan doesn't suck air through (or where it sucks very little through) and put a small piece of coroplast on the front side of the radiator to block air from blowing over the probe.
Bringing this thread back to the top, for results and update.
Remember, I have been running a weak v6 camero fan with a radiator probe switch for a few months, all wired up all hacked looking with zip ties. Now putting in a fan out of Lincoln Mark VIII, known for being a junkyard jewel, because for $20 or so you get a fan that out performs most aftermarket fans. (It takes a lot of amps to run it, so you need 10 gauge wire, a big relay, and diode.)
Bought a radiator cooling fan switch/thermostat at Napa "for a 87 Buick Grand National" I wired it up this morning, and finally put in the Mark VIII fan too. I researched online for how to wire it up for low speed, and apparently, I don't think it is a two speed fan! Unlike some of the Taurus fans! I took it for a test drive, and it works. It "deep cycles" it seems. It runs for 30-60 seconds or so. The radiator gets cold, and I think it just takes time for the cool water to flow through the whole engine, to the thermostat housing, where I have my temperature sensor. Then it finally shuts off. Its not a bad thing, it won't be cycling as often as my old setup. So I went back home and I have hot wires. I originally thought I could get buy with thinner wires and smaller relay, but as I said earlier, it doesn't have a low speed. So now I am just going to do it right this time, and finalize the wiring for this baby, the right way. a 75 amp relay cost a whoppin' $65 (I wasn't going to pay that!), so instead I went to the junk yard hoping to find a high capacity relay. Most relay's AMP ratings aren't marked. But I found a 70 AMP relay in Large Ford cars. Also found an AWESOME relay box! Look for late model Mercury Grand Marque's. Surprisingly, they don't seem to come in the Ford Crown Victoria's, though. It is located at the top of the passenger fender. It is very small for a relay box, It holds one high capacity 4 pin relay, and one regular 4 pin relay. I discovered that a Ford 2 pin diode fits perfectly into the regular relay slot! This relay box demensions are about 4" by 2" and 4" tall. It mounts very easily too! Pictures coming soon.
So to summerise, 80 Bucks gets you the whole fan system that looks stock. 25 for the fan, 35 for the thermostat switch, 10 for the relay mini-box w/ relay and diode, and about $10 in wiring supplies.
85 Chevrolet. 30 MPG or bust!
Couple of things, the DC Control unit is an excellent piece. I've used 2 of them so far, in 2 different vehicles. I've had no problems with the temp probe taking its reading from between the radiator fins as is as the DC Control probe is insulated. I do know the Flexalite controllers have had a problem with this. The fix is simple, you put a little silicon across the front of the fin hole that the probe fits into.
The real advantage to the DC Control unit is it allows a constant temperature to be put into the radiator, so the temperature doesn't spike as it does with the simple thermostatic switch. And, it brings power on slowly instead of instantly, which is much easier on the electrical system. Having a constant temperature means you can run the temperature at a hotter level than with a spike system, and a constant, steady temperature is better for power and economy.
On top of this, only one sensor is required, no need for a low speed and high speed sensor. The fans don't need this because the factory sent them out this way, the factory sent them out this way because thermoswitches are cheap when you buy them by the million. The factory has since moved to direct computer control for the fans, but still uses the 2 level fan control because the hardware and programming is cheaper that way.
On the fans themselves, they are simple electric motors. They don't require either full power or no power, so there should be no concerns about using a factory fan with an aftermarket controller. They will work just fine.