I guess I would do the opposite of what you intend to do.  I would like an accurate true engine temperature and I think the location on the manifold is better than any of the options you llisted for a temperature sensor.  The fan doesn't need to come on unless there is flow so, if your t-stat got stuck, for example, the fan would turn on but you may not be aware that your temps are out of control.  A short tube with a bung on the radiator return line would work for the fan and if properly used, a radiator sensor would detect warm coolant flow in the radiator when it is time to turn the fan on.  Some are adjustable to account for positioning.

At one time I had a t-stat housing that had a tapped hole after the t-stat that would work in your application as well.  What engine and belt/water pump/t-stat setup are you running?
 

I just got through with a car having an Air Gap intake.  He wanted two gauges connected, the factory one and an aftermarket.  He originally installed a pipe tee sticking up from only available hole in the manifold and had one in the horizontal part of the tee and one in the vertical part.  Both gauges read inaccurately because their sensors were not submerged in the coolant.
I removed the T and installed the factory gauge back where it belonged.  Luckily the aftermarket gauge used a sensor that attached in a 1/8" NPT hole.  So, I drilled a hole in the intake near the original sensor hole and threaded the hole and installed the sensor.  I do not think I would try that if you have larger than 1/8" pipe thread size.  Be sure to place the hole far enough away from the distributor to not interfere with distributor movement.

Otherwise my usual advice stands:  Put a real fan on it and never look back.  You will Never have problems with it like you are inducing with an electric fan.  Just my usual, unsolicited, unappreciated worldly advice.

GPatrick wrote:

I guess I would do the opposite of what you intend to do.  I would like an accurate true engine temperature and I think the location on the manifold is better than any of the options you llisted for a temperature sensor.  The fan doesn't need to come on unless there is flow so, if your t-stat got stuck, for example, the fan would turn on but you may not be aware that your temps are out of control.  A short tube with a bung on the radiator return line would work for the fan and if properly used, a radiator sensor would detect warm coolant flow in the radiator when it is time to turn the fan on.  Some are adjustable to account for positioning.

At one time I had a t-stat housing that had a tapped hole after the t-stat that would work in your application as well.  What engine and belt/water pump/t-stat setup are you running?
 

I thought about switching to the other type of sensor but then am out the money I spent in the controller I have now. Since the sensor is wired to the module I can't just replace that part.

And I tried looking for the thermostat housing with the bung but the only ones I could find are like the one I have - with a radiator hose and hose from housing to water pump. As far as your other question - 5.0 block, stock style 66 289 water pump and thermostat housing as well as stock belt configuration.

MS wrote:

I just got through with a car having an Air Gap intake.  He wanted two gauges connected, the factory one and an aftermarket.  He originally installed a pipe tee sticking up from only available hole in the manifold and had one in the horizontal part of the tee and one in the vertical part.  Both gauges read inaccurately because their sensors were not submerged in the coolant.
I removed the T and installed the factory gauge back where it belonged.  Luckily the aftermarket gauge used a sensor that attached in a 1/8" NPT hole.  So, I drilled a hole in the intake near the original sensor hole and threaded the hole and installed the sensor.  I do not think I would try that if you have larger than 1/8" pipe thread size.  Be sure to place the hole far enough away from the distributor to not interfere with distributor movement.

Otherwise my usual advice stands:  Put a real fan on it and never look back.  You will Never have problems with it like you are inducing with an electric fan.  Just my usual, unsolicited, unappreciated worldly advice.

I learned the lesson with the T - I couldn't get the fan to turn on consistently. I did see a boss that I could drill on the manifold but an using that as a last resort. Do you have an opinion on drilling and tapping the heater hose fitting? It is perfectly flat, I can removed it, and if I screw it up I am only out the cost of the fitting.

MS wrote:

I just got through with a car having an Air Gap intake.  He wanted two gauges connected, the factory one and an aftermarket.  He originally installed a pipe tee sticking up from only available hole in the manifold and had one in the horizontal part of the tee and one in the vertical part.  Both gauges read inaccurately because their sensors were not submerged in the coolant.
I removed the T and installed the factory gauge back where it belonged.  Luckily the aftermarket gauge used a sensor that attached in a 1/8" NPT hole.  So, I drilled a hole in the intake near the original sensor hole and threaded the hole and installed the sensor.  I do not think I would try that if you have larger than 1/8" pipe thread size.  Be sure to place the hole far enough away from the distributor to not interfere with distributor movement.

Otherwise my usual advice stands:  Put a real fan on it and never look back.  You will Never have problems with it like you are inducing with an electric fan.  Just my usual, unsolicited, unappreciated worldly advice.

 

 Your advice is OK here Steve. I went through the electric pusher , puller , sensor here, sensor there and finally  put on a tried and true mechanical. My 331 now holds at 180 in 90 degree weather in traffic with the air on.
  I don't miss the extra horse power that the "real" fan eats up.

You can also buy an aluminum sleeve that splices into the lower radiator hose that has a threaded bung for a drain petcock (1/8" npt), that you can use for a temperature sensor. I hooked one up there to see what the differential temperature was across the radiator.

I bought this one - http://www.oreillyauto.com/site/c/detail/MRY0/84831.oap