How hot is too Hot??

[Stang72]

Hi Guys and Gals,

I have a 1972 Mach 1 that runs the original 351 Cleveland Q Code Motor.  It runs dual electric fans behind a big alloy radiator-Car has a 180F Thermostat in it. I have had to replace the thermo switch for the fans as it had gone bad and am not having the greatest of luck.  I put a 190F On/175F off in the car on the weekend, however the Fans didn't actually come on until around 205F (I know these switches aren't the most accurate things in the world......).  I'm just wondering if this is far too hot for the motor before the fans come on??  I obviously don't want to cook the thing.  Any help/opinions would be greatly appreciated :)

Thanks Dan

[Chris66pny]

Switching on at 190F is good, that's where I've got mine set. 205F is starting to get a bit hot for my liking, if the fans pull temperature out of it quickly its not too much of an issue.

You can always check out the davies craig fan controllers to get better control over the fans, easy to install and are far more accurate than a switch.

https://daviescraig.com.au/product/digital-thermatic-fan-switch-12v-24v-0444

[Stang72]

Switching on at 190F is good, that's where I've got mine set. 205F is starting to get a bit hot for my liking, if the fans pull temperature out of it quickly its not too much of an issue.

You can always check out the davies craig fan controllers to get better control over the fans, easy to install and are far more accurate than a switch.

https://daviescraig.com.au/product/digital-thermatic-fan-switch-12v-24v-0444

Hey Chris,

Thanks for the response. How did/would you mount the temperature probe? Do you just slide it into the top radiator hose where it meets the radiator?
Appreciate the help! 

Dan

[Chris66pny]

I welded a bung on the side of my radiator and got the NPT sensor kit. There might also be a NPT mount in your thermostat housing you can use. You can just feed the temp probe in the top radiator hose but it can leak if not sealed well.

[USA066]

Hi Dan,

I have a big alu radiator 26” with dual fans in my 66 with a SB 302/331.

I have installed a Craig Davies digital (not manual) Part #0444 fan controller. The probe is installed through the radiator fins near the hot inlet hose. Don’t install in the hose as it will snap off due to water turbulence. I had two fail, but no problems since installing through the fins. As the air temp around the probe is about 15 degrees below the coolant temp, you need to set the On temp at around 15 degrees below your thermostat temp. So, with my 180 degree thermostat, I have my fans set to switch On at 161 degrees. This could be the issue with your fans coming on at 205 degrees.

I have also installed a temp only Engine Watchdog. As this takes temp sensor readings from the engine block NOT coolant temp, I have mine set to alarm at 201 degrees. Best investment I’ve ever made. You can also buy these with Oil Temp and fan controller.

Also, with dual fans, I would advise to get your fans wired separately with two circuit breakers. The thinking here is that if one fan trips, the other fan will continue to run. Just some further protection.

Colin

[Stang72]

Hi Dan,

I have a big alu radiator 26” with dual fans in my 66 with a SB 302/331.

I have installed a Craig Davies digital (not manual) Part #0444 fan controller. The probe is installed through the radiator fins near the hot inlet hose. Don’t install in the hose as it will snap off due to water turbulence. I had two fail, but no problems since installing through the fins. As the air temp around the probe is about 15 degrees below the coolant temp, you need to set the On temp at around 15 degrees below your thermostat temp. So, with my 180 degree thermostat, I have my fans set to switch On at 161 degrees. This could be the issue with your fans coming on at 205 degrees.

I have also installed a temp only Engine Watchdog. As this takes temp sensor readings from the engine block NOT coolant temp, I have mine set to alarm at 201 degrees. Best investment I’ve ever made. You can also buy these with Oil Temp and fan controller.

Also, with dual fans, I would advise to get your fans wired separately with two circuit breakers. The thinking here is that if one fan trips, the other fan will continue to run. Just some further protection.

Colin

Hi Colin

Thanks so much for the advice, really appreciate it! Will look into it for sure 

[Edz]

I agree with comments above.

I had a bung welded in the side of the radiator by my local radiator shop and they supplied a sensor to screw in ($50 all up), use this to trigger fan relays - plural. Much more reliable and cheaper than a Davies Craig system with thermocouple stuck inside the radiator hose. You can see the radiator pic below. I think it trips at 88C. Very simple wiring, one end of the sensor goes to earth, the other end goes to the relay to close it.

After having a 2 pin plug melt in peak hour traffic in Sydney driving a 16" Spal fan, I now run 2 x 30 amp relays with separate plugs and relays to run the fan. The fan can draw 20 to 25 amps and the plugs will melt. Running two plugs mean they only pull 10 to 12.5 amps each which they seem to cope with. I have since switched to the dual Mondeo fan setup which fits the big block radiator beautifully in my 66 and still use the dual setup and have had no problems since.






This is the wiring circuit I used for the dual fans - controlled by the dual msd fan signals. If you connect the radiator switch input to where mine says 'fan dash override' when the switch closes (hot 88C) it will pull the relays to earth and close the, triggering the fans. You can also have a manual switch here on your dash to trigger them manually so you can turn them on early if you want?

https://i.ibb.co/6X5kBxp/dual-fan-wiring.png[/img]]