Power to radiator fans on key vs on temp sensor

[TomsResto]

Question: Any reason why you wouldn't recommend having the radiator fans kick on with keyed power (in a restomod/pro touring build) and only have them kick on with temp sensor reading of 185+ degrees, in a car that will never be run in ambient air temperature below 40-50degrees

Details behind the question:
I have a Ramjet 350 setup in a 69 Camaro with Vintage A/C and dual fan (Speedway brand, blowing from inside engine compartment into back of a larger than 69 OEM aluminum radiator).

Had an issue on a hot/high humidity day in Iowa (100 degree heat index, air temp around 90) where the fans didn't kick on and coolant temperature climbed to about 218 (with temp sensor the relay kicks the fans on at 185 degrees) when I was stuck at a stoplight. Not a big deal, I took a route that quickly got me out onto a 45mph road and turning low rpm's with air moving through front side of radiator she cooled back down to 180 pretty quickly, but not certain on what was going on I brought it back home, parked in the shade and popped the hood.

After letting her sit for an hour or so I roller her back over and the fans came back on. From best I can tell the issue stemmed from the relay to power the fan was placed behind the grill work on the front side of the bracket between radiator mounts and driver's headlight so it got wet when I washed the car before taking it out for a ride and the relay housing was not weather/water tight. As a "quick fix" to prevent recurrence I taped up the relay in black electrical tape and ordered up same sized replaced relay housed in a weathertight enclosure (~$20 from JEGS).

I recently shared the story with a few others in context of my intent to run some longer hauls (Hot Rod Power Tour) and maybe a couple fun runs through some autocross cones, and the recommendation by a trusted source is to just ground the lead to the temp sensor, effectively keeping the relay providing power to the fans when there is 12v applied (i.e. key turn to accessory & run position). The theory behind it seems to be that then you know the fans are always turning, especially if running the A/C on a long haul when you have the windows up and don't "hear" whether the fans are actually running and given that it's not a daily driver that will ever see temperatures anywhere near/below freezing (maybe a fall day run in the 50's would be all the cooler of a day I have her out) so having the fans always run shouldn't create any hard conditions on the engine (i.e. coolant lower than desired for any extended period of time).

Seeking any thoughts from those that have deliberated this topic on their own builds or started out one way and went the other and why.

[BonzoHansen]

If you run the fans non stop you'll prematurely wear out the fans, and you wont properly control engine temperature. Which will screw up your efi.

Why do you need to know your fans are running? Doesn't your temp gauge tell you that? Guess if you need a warm and fuzzy feel you could wire an LED off the fan power side of the relay to come on when it has power.

[csouth]

You say the fans are blowing on the radiator from inside the engine compartment. I know that Speedway has reversible fans, is the setup as a push or pull? If its setup as a push, I thought it needed to be on the other side of the radiator?

[TomsResto]

I think you're right now that I think about it further, my bad... was thinking of some of the four stroke snowmobile applications I've dealt with in the past where radiator isn't necessarily mounted in the air flow stream because you are trying to preserve engine heat and only push some air past if at idle with no air movement or no new snow being kicked up on heat exchangers (nothing crazier than getting a high temp warning light on your Yamaha Nytro while idling on a frozen lake staring at your map by the headlight with the wind howling dropping the wind chill to -30F).

Mounted behind radiator in this should be a "pull" ... guess it wouldn't make sense if it was trying to "push" into the back side of the radiator while running down he road and it would be "fighting" the incoming air flow from the road.

[TomsResto]

Confirmed by quick speedway product info web search:
"Help your vintage engine keep cool by adding an electric cooling fan to your radiator. Electric fans are far more efficient than mechanical engine driven fans because they free up horsepower and only run when you want them to (when used with a fan controller, not included). Plus, most electric fans can be mounted ahead of the radiator or behind the radiator, with the more efficient location being on the engine side of the radiator. The fan is supplied as a "puller" to mount behind the radiator, but it can be changed to a "pusher" by reversing the wires, flipping the fan blade and mounting in front of the radiator."

[csouth]

OK, so we know that is not the issue. What fan controller are you using? I personally wouldn't want my fan running all the time just because your motor will never reach optimum temp.

[BBPanel]

Why wouldn't the thermostat control that?

OK, so we know that is not the issue. What fan controller are you using? I personally wouldn't want my fan running all the time just because your motor will never reach optimum temp.

[TomsResto]

I'm not sure if I'm with you on the "never reach optimum temp" aspect ... pretty sure (if I remember correctly) in traditional systems with a mechanically driven fan that fan is spinning all the time the engine is running (even immediately on "cool" starts when the coolant temp is equal to ambient air temp)... delayed yes, but not never

[TomsResto]

Why wouldn't the thermostat control that?

Normally it would, but the question/suggestion being pondered here is to bypass that thermostat by grounding it so as to ensure overheat due to failed sensor is avoided

[Vegas 69]

OK, so we know that is not the issue. What fan controller are you using? I personally wouldn't want my fan running all the time just because your motor will never reach optimum temp.

THERMOSTAT?

The engine will get to the proper operating temp as determined by the T-Stat even in minus 20* weather with the fans running on full

[csouth]

THERMOSTAT?

The engine will get to the proper operating temp as determined by the T-Stat even in minus 20* weather with the fans running on full

I would think that fans pulling cool air into the engine compartment constantly vs a thermal cycle would keep the engine significantly cooler? Judging by the adverse reaction I guess this is not the case?

[BBPanel]

..... to bypass that thermostat by grounding it so as to ensure overheat due to failed sensor is avoided

You lost me on that - the thermostat is a mechanical device - what does grounding it do?
If all you really want to know is if the fans are on install an indicator light and perhaps also have an override switch so you can turn them on whenever you want.

[TomsResto]

You lost me on that - the thermostat is a mechanical device - what does grounding it do?
If all you really want to know is if the fans are on install an indicator light and perhaps also have an override switch so you can turn them on whenever you want.

I shouldn't have used thermostat... my reference was to the fan switch (the don't use the term thermocoupler in the description on product search, but it uses a ground wire to turn the electric cooling fan on) that senses the coolant temperature in the block (>185) and sends signal to the relay that powers the electric fans mounted to the radiator. Similar to this one (I didn't do an exact product match, just quick search on Speedway) : http://www.speedwaymotors.com/AFCO-8...FQaqaQodqfoCAA

Also circled in bullseye red in the attached image as currently installed (where it controls fans by the coolant temp in the head)

Your point is valid (as is Vegas69) that the mechanical "thermostat" will keep the coolant from flowing through the radiator and allow it to climb to desired operating temp at the same rate as it does otherwise, not caring whether the radiator fans are spinning keeping that coolant cool. That was an excellent point that I failed to think of as well, and I think aids in addressing the concerns CSOUTH was identifying.

[TomsResto]

Thanks everyone for all the input and thoughts on this topic ... I think in a nutshell the summary I'm taking away from this discussion is that I should continue to use the setup as currently installed (fans turn on/off with the fan sensor that grounds the relay that powers the fans when coolant temp in the head climbs over 185). It's functional as is, and my local trusted source that is advising me to bypass and run the fans at all "key on" situations is reacting to past issues that he's experienced in supporting those who are doing long hauls like Power Tour. However, I do like the idea of being able to force the fans to run if I'm in a situation where I suspect any issue with that temp switch not grounding and effectively sending the signal to continually spin the fans. As Bob suggested I could either do that as an "over-ride" switch or maybe another less elegant but effective option would be to hang a grounded line and tie that off where it's long enough and accessible when I raise the hood and I could move the end of that line to the connection jumper on the current fan switch sensor probe (whatever that thing should be called) and with a quick switch of connectors then that would keep the fans spinning if I'm on a longer haul cruise, running the A/C constantly, etc.

I'm new to the forum and obviously flubbed up a few words/attempt to describe my question but no one flamed me or talked down to me ... great forum, I'll be active here going forward and looking for opportunities where I can weigh in and try to help others in a respectful manner.



Thanks,
Tom