• Hello there guest and Welcome to The #1 Classic Mustang forum!
    To gain full access you must Register. Registration is free and it takes only a few moments to complete.
    Already a member? Login here then!

Fan on/off for a 195 degree thermostat.

Street66

Street66

Member
Since the Chuckster has appeared Id thought Id ask if he still stands behind this reccomendation. I had to go back to 2015 to find an answer from the other site since he was already gone. back then you said,

"A 195* thermostat will be fully open at 210-212*F. I'd have the fan come on at 220*F and shut down at 210*F. That should keep the fan off during cruising when there is adequate airflow through the radiator. Lower than that and the fan is going to pretty much run constantly as your water temp modulates between 195*F and 212*F."

Is this still your reccomendation Bart? Kep in mind I have a Dart block and Aluminum heads (AFR 185).

Thanks in advance
 
I have mine set at 215 on and 200 off. Mine is rarely on. It will come on on hot days sitting at a stop light or when tuning for an extended time while idling. It will turn off when idling after a couple minutes. Tstat is 195.

My logic is simple 1.) the engineers designed that when these cars T stat opened the fan would be running (as the mechanical fan was always running) 2.) Off at 200 is to keep it in a fairly narrow range to minimize differential expansion cycles between cast iron and aluminum.
 
Last edited:
"Stock" Ford thermostat was a 190*F... Motorcraft # RT-9, Ford P/N A8AZ-8575-C. The "default replacement" is a 195*F thermostat... my recommendation is: https://flowkoolerwaterpumps.com/products/robertshaw-330-160-degree-thermostat?variant=9125073354804

As for electric cooling fan "on/off", I haven't changed my mind.... on at 220*F, off at 210 or even 215*F.... As the fan is redundant above around 25 mph there's no reason to have it run when movement of the vehicle will provide adequate airflow. Now, if you have a 195*F thermostat and your car is running hotter than 220*F going down the road, it ain't the fan and it's time to "dig deeper".
 
bartl said:
"Stock" Ford thermostat was a 190*F... Motorcraft # RT-9, Ford P/N A8AZ-8575-C. The "default replacement" is a 195*F thermostat... my recommendation is: https://flowkoolerwaterpumps.com/products/robertshaw-330-160-degree-thermostat?variant=9125073354804

As for electric cooling fan "on/off", I haven't changed my mind.... on at 220*F, off at 210 or even 215*F.... As the fan is redundant above around 25 mph there's no reason to have it run when movement of the vehicle will provide adequate airflow. Now, if you have a 195*F thermostat and your car is running hotter than 220*F going down the road, it ain't the fan and it's time to "dig deeper".
Click to expand...
I bought the Mr Gasket copy of the Robertshaw. Is this ok or should I ditch it for the one you posted?
 
Is there any downside to an electric fan being on when the car is moving?

The airflow is already spinning the fan. There's very little, if any, load on the motor. Some people even use a relay with a diode to prevent backfeeding.
 
bartl said:
"Stock" Ford thermostat was a 190*F... Motorcraft # RT-9, Ford P/N A8AZ-8575-C. The "default replacement" is a 195*F thermostat... my recommendation is: https://flowkoolerwaterpumps.com/products/robertshaw-330-160-degree-thermostat?variant=9125073354804

As for electric cooling fan "on/off", I haven't changed my mind.... on at 220*F, off at 210 or even 215*F.... As the fan is redundant above around 25 mph there's no reason to have it run when movement of the vehicle will provide adequate airflow. Now, if you have a 195*F thermostat and your car is running hotter than 220*F going down the road, it ain't the fan and it's time to "dig deeper".
Click to expand...
I went back to my mechanical fan and redid my shroud so it is 3/4” spacing from the fan tips to the shroud. Works great now.

That being said, I did the HRPT this year with my 24” radiator and dual Contour fans setup. The shroud must be quite an impedance to flow even with the cutouts in the shroud with flaps. I say this because with my fans we’re set to come on at 213 and off at 205 when I was doing 60 mph in 85 degree ambient temps my coolant temp would would reach the 213 mark and the fans would kick on. If I turned the fans on then the coolant temp would stay 205-207.

With my mechanical fan and the properly fitted shroud, at 95 degrees ambient temps doing 60 mph the coolant temp is 200-203. But it is not a clutch fan so it turns constantly.

Allen
 
67DropTop said:
Is there any downside to an electric fan being on when the car is moving?

The airflow is already spinning the fan. There's very little, if any, load on the motor. Some people even use a relay with a diode to prevent backfeeding.
Click to expand...
Backfeed would be the principal problem, plus armature/brush wear. The biggest issue is inhibitiion of airflow when the push of air from vehicle movement exceeds the cfm capacity of the fan. Either the fan will not spin any faster, or overspeed will cause backfeed voltage will exceed design parameters. The best possible electric fan would be one with a cfm capacity that matches the maximum practical airflow coming in through the front.
 
bartl said:
Backfeed would be the principal problem, plus armature/brush wear. The biggest issue is inhibitiion of airflow when the push of air from vehicle movement exceeds the cfm capacity of the fan. Either the fan will not spin any faster, or overspeed will cause backfeed voltage will exceed design parameters. The best possible electric fan would be one with a cfm capacity that matches the maximum practical airflow coming in through the front.
Click to expand...
Assuming use of an electric fan with a cfm capacity that matches the maximum practical airflow coming in, is there any downside to the switch being 'on'?
 
67DropTop said:
Assuming use of an electric fan with a cfm capacity that matches the maximum practical airflow coming in, is there any downside to the switch being 'on'?
Click to expand...
I'd guess not.... Would be interesting though if they made the fan with a one-way clutch so it would free-spin on the shaft when not under power. Would save wear and tear on the fan motor....
 
You must log in or register to reply here.
Back
Top