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Thread: Cooling fans shut off at highway speeds. Fans work correct with AC at lower speeds

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    Cooling fans shut off at highway speeds. Fans work correct with AC at lower speeds

    I am trying to wrap my mind around adjusting my cooling fans. My vehicle is an 08 Avalanche with a 5.3ltr (gen4) and On3Performance turbo. Truck runs great but gets hot when you are on the highway towing. I noticed that the cooling fans shut off on the highway and don't respond to the temp settings. The vehicle was 230 degrees and no fans were on however my desired % vs ECT showed 90% at 200 degrees and above. All the fan settings I can adjust are in percentages however my factory fans only have high and low relays. It's the regular 3 relay deal that commands both fans on low and or high. There is no fan percentage control that I know of in my truck. If I look at a Gen 3 tunes it looks like the correct fan control settings for my truck. Is there a way to put the older fan control version and attach it to my current tune in my truck? If so, how?

    On a side not. I reached out to tech support and they told me to download the newest beta version and it would have more fan settings. I did do that and there is a setting for Lo & high vs mph so I am going to try to raise those settings and see what happens. But again all the desired settings are in percentages not just a low fan at this temp and high fan at this temp. Very confusing.
    Last edited by Thyen; 07-28-2020 at 03:26 PM.

  2. #2
    Advanced Tuner IARLLC's Avatar
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    Chris and some of the other guys explain GEN4 fan operation on this link:
    http://www.hptuners.com/forum/showth...light=LS2+fans

    If you search the GEN4 section for fan related content you will see that several of us have taken quite a bit of time to explain it.

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    Ok thanks Chris. Sorry I am new to form and didn't see it. I finally found my culprit. After using the beta version there was a Lo & High vs MPH table that had the fans not operation between 50 mph and 65mph which is exactly the speed I tow at on back roads. Engine was cooking and no fans were commanded. That was frustrating to find.

  4. #4
    Advanced Tuner IARLLC's Avatar
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    Cool! Glad you figured it out.

    Kinda crazy with that much speed/airflow that the fan still makes a difference above 50. I would not have guessed.

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    Got to keep in mind I have a turbo inter-cooler in front of the radiator and AC condenser. Without a doubt it keeps temps lower when towing on the highway when cooling fans are on high. I also added a blanket on turbo and a cowl hood to let the heat out. I just towed the other day after turning off the mph ect fan settings and for some reason it still turns the high fan off occasionally when engine temp is high. I don't get that but I am gonna try to lower the AC pressure table to command high fan at a lower pressure. We will see how that goes.

  6. #6
    Advanced Tuner IARLLC's Avatar
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    OK. That makes some sense. The cowl hood helps let heat out at low speed but as the speed goes up the high pressure created at the base of the windshield actually fights airflow coming through the radiator. Venting the hood right behind the radiator and/or near the sides of the hood sucks hot air out of the compartment at speed. I would be curious about back to back 60 mph coolant temp tests with the cowl blocked of and open. Just a thought.

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    That's a good idea. I was thinking of installing vents in the hood but couldn't decide where to put them. Hood has no other venting except in back right now but without it, the engine overheats. Turbo is just packing too much. I always wanted to do a rear turbo just for that reason but no one seems to sell those kits anymore. Oh well, too late. Got to make this one work because I am already committed. I will let you know, thanks for the feedback.