Cooling fan setpoints

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  • chevynut
    Registered Member
    • Nov 2011
    • 11030
    • 115
    • Fort Collins, CO

    Cooling fan setpoints

    I have been researching what setpoints to use on my cooling fans and have run across some really idiotic stuff about cooling systems. So many guys think a thermostat can solve a cooling problem and swear that by changing theirs out to a lower rating it fixed the problem. And the "slow the coolant down so it has time to cool in the radiator" bullshit still persists all over the internet. It's entertaining to read some of the stuff. Some guys think they can defy the laws of physics, and some don't even believe in physics....I ignore those guys.

    Anyhow, I read that a Fbody LS engine is supposed to have a 187 degree thermostat which I read from several sources. That seems fine but it wouldn't be fully open until around 197-200 degrees. So driving down the highway the engine should run in the 190-200 range unless it's really hot outside. I think the fans are locked out above a certain speed. What surprised me is the fan setpoints.. The fans are wired such that they run in series at half speed when the first setpoint is reached, and in parallel at full speed when the second setpoint is reached. Mine are wired the same way. With the A/C on the fans run at high speed.

    Here's what I found for the F-body fan setpoints which seems awfully high....I know they do it for emissions....

    Fan 1 on/off at: 227
    Last edited by chevynut; 08-17-2024, 10:09 AM.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax
  • chevynut
    Registered Member
    • Nov 2011
    • 11030
    • 115
    • Fort Collins, CO

    #2
    Well I wrote a lot more than that, but it seems we have a limited number of characters or something. I can't even edit it and add the fan 2 settings. Sigh.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

    Comment

    • 55mike
      Registered Member
      • Mar 2012
      • 221
      • 225
      • Annabella Utah

      #3
      When I installed the Sniper FI system, I installed the temp sensor in the cylinder head (AFR aluminum, SBC). It's well known the Holley provided sensor doesn't read correctly, so, I replaced it with the correct AC Delco unit. I can attest the water temp reading in the cylinder head is about 8-10 degrees warmer than at the t-stat housing. So.... with this in mind, I set the fan(s) (twin Spal 10") to activate at about 205 degrees, and to stop at about 195 degrees. Interestingly, when warming up from completely cold, the Sniper temp reading will go to about 195-200, then when the 180 t-stat opens, it quickly cools down to about 185 or so. IF I'm driving hiway speeds, even on a hot day, the temp will hold steady at 185-190 (head temp) and the fans have no need to activate at all. I use a large cross-flow radiator in the 6 cyld position.
      sigpic

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      • chevynut
        Registered Member
        • Nov 2011
        • 11030
        • 115
        • Fort Collins, CO

        #4
        I have two temperature sensors, one Dakota Digital sensor for the VHX and fan controller, and one for the TerminatorX. From what I have seen they both read very close to the same temperature. They're both next to the water neck in the intake manifold, side by side. I only use the TerminatorX fan output for an over-temperature warning that turns on the "check engine" light. The Dakota Digital PAC-2750 fan controller is connected to the VHX via the BIM interface, which eliminates the need for another sensor.

        I have a custom PRC radiator in a custom radiator support, with dual 13" 4000 CFM Derale fans. I run them at half speed at the .low setpoint and full speed at the high setpoint using the same 3-relay circuit as the F-bodies. At 4000 CFM I calculate the air speed through the fans to be about 25 MPH.

        When cruising on the highway, I have the Pak-2750 set up to disable the fans at about 35 mph, since at this speed I'm pushing more air through than the fans can pull. So at that point the thermostat controls the engine temperature if I have enough cooling capacity. I think I'm going to set up my fans for.....

        Low setpoint on/off 195/185
        High setpoint on/off 205/195
        Warning light on/off 215/210

        What this will do is turn the fans on low speed at 195, and if there's enough cooling capacity they'll turn off at 185. If they can't keep the engine cool and the temperature keeps climbing, the fans kick into high speed at 205. They go back to low speed at 195 and will cycle between those two temperatures.

        56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


        Other vehicles:

        56 Chevy 2-door BelAir sedan
        56 Chevy 210 4-door sedan
        57 Chevy 210 4-door sedan
        1962 327/340HP Corvette
        1961 Willys CJ3B Jeep
        2001 Porsche Boxster S
        2003 Chevy Silverado 2500 HD Duramax
        2019 GMC Sierra Denali Duramax

        Comment

        • WagonCrazy
          Registered Member
          • Mar 2012
          • 1879
          • 530
          • Santa Clarita, CA

          #5
          When cruising on the highway, I have the Pak-2750 set up to disable the fans at about 35 mph, since at this speed I'm pushing more air through than the fans can pull. So at that point the thermostat controls the engine temperature if I have enough cooling capacity. I think I'm going to set up my fans for.....

          Low setpoint on/off 195/185
          High setpoint on/off 205/195
          Warning light on/off 215/210

          What this will do is turn the fans on low speed at 195, and if there's enough cooling capacity they'll turn off at 185. If they can't keep the engine cool and the temperature keeps climbing, the fans kick into high speed at 205. They go back to low speed at 195 and will cycle between those two temperatures.
          I think your numbers are sound. I'm running a stock LS1 (aluminum block and heads) and using the stock ECU to control the fans. The issue I've always had since the beginning is the fans never kick on, regardless of the temp. I can't verify the ECU is actually sending a ground signal out (either high or low setting). So I wired in a manual switch that I control when things get hot.

          Yesterday, returning home from a car show, the outside temp was 95 and when on the freeway (70mph) and without the fans on, it ran at about 210...which is fine. When slowing speed to under about 20mph, it starts to climb a bit so manually turning on the fans (high) keeps it about 210.

          I need to get it into someone with a HPTuner to verify what the ECU temps have been set at. I suspect the guy that did the programming might not have set them right.

          I'd also like to do slow speed fan on at 195, off at 185.
          High speed fan on at 215, off at 205

          Once a few years ago, I let it go without running any fans on a hot day (just to see if they would eventually come on) and at about 230+, the steam started to come out of the radiator cap. I don't let it get that high when driving it now.
          1957 Nomad- LS1/T56 on C4 chassis
          1959 Fleetside Apache 1/2 ton, shortbed, big window, 327ci.

          Comment

          • Rick_L
            Registered Member
            • Apr 2012
            • 4676
            • 571

            #6
            Low fan off must be higher than than thermostat fully open temp. I would set at 205. Fan on at 215.

            Comment

            • chevynut
              Registered Member
              • Nov 2011
              • 11030
              • 115
              • Fort Collins, CO

              #7
              Originally posted by Rick_L
              Low fan off must be higher than than thermostat fully open temp. I would set at 205. Fan on at 215.
              Not sure I understand why you'd want to run that hot. We're talking about low-speed and idling conditions in warm weather. Why would you wait to turn the LOW fan on until 205? That means the high fan shouldn't turn on until 225 and off at 215. That seems way too hot to me. In hot weather the engine would always be around 220.

              I think the 180 thermostat should be fully open by 190 or so. If I turn the fan on at 195 and off at 185 the thermostat is still open approximately halfway when it's turned off. The low fan should cycle around 190, which is about when the tstat is fully open. The high fan, which is what's probably going to control the temperature under those conditions, cycles around 200. I doubt the low fan ever turns off.

              I'll have to play with it and see how it acts.
              56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


              Other vehicles:

              56 Chevy 2-door BelAir sedan
              56 Chevy 210 4-door sedan
              57 Chevy 210 4-door sedan
              1962 327/340HP Corvette
              1961 Willys CJ3B Jeep
              2001 Porsche Boxster S
              2003 Chevy Silverado 2500 HD Duramax
              2019 GMC Sierra Denali Duramax

              Comment

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