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electric fan temp sending unit location?

Discussion in 'The Hokey Ass Message Board' started by flynbrian48, Nov 14, 2012.

  1. flynbrian48
    Joined: Mar 10, 2008
    Posts: 6,610


    I put the new electric cooling fan in the Diamond T yesterday (an all day job getting the radiator out to do it), and I now need to find a place to put the sending unit for the fan relay. The radiator is a '93 GMC van crossflow mounted on end, with the original filler neck on the bottom. Right next to the filler on the (now) lower tank is a heater hose boss that will be unused. Is there any reason I can't simply put the sender in a short piece of heater hose and run it there (since I need to plug this anyway)?

    It's an LS motor, I'm already using the passenger side cyl. heads boss for the SW temp gauge sender, and the drivers side one has the factory harness' sender in, which I (think) I still have to have talk to the ECM. Perhaps I'm overthinking the difference between rad. coolant temp and cyl. head temp. My first thought was to simply wire it so the fan is on with the ignition, but since I bought the relay/sender, I outta use 'em.

  2. Brian,
    I have always considered that best place for the sender to be next to the T stat. I imagine that this is not a good place or that there is not provision for that on your engine.

    If the bung is near return water to your radiator then that bung should work, thw T Stat will open and your fan will come on given that they are the same value. this should work well for you.

    By the way have I ever told you that I really like that hauler?
  3. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,658

    V8 Bob

    I would look into a programmable fan controller, that uses an existing temp gauge sender, like the one from Spal that I'm using. :)
  4. flynbrian48
    Joined: Mar 10, 2008
    Posts: 6,610


    Porknbeaner you're right, there's no boss for a sender next to the t'stat, but now that you mention it, I COULD use the heater hose line there for the sender, and put the heater hose on the that outlet on the lower tank.

    Glad you like it, I think it'll be a pretty nice rig.

    V8 Bob I didn't know about the programmable ones, I'll look into that too.


  5. drptop70ss
    Joined: May 31, 2010
    Posts: 1,152

    from NY

    I use adjustable sending units, a few more bucks but worth it. That way no matter where you put the sending unit you can adjust the controller to compensate. I watch the temp gauge and when it hits my magic number (normally 190 degrees) I adjust the controller to turn on the fan. This is of course after verifying my temp guage is accurate, I normally use the thermostat to do that. If you do not have an easy place to put a threaded sending unit you can use the ones that slide into the radiator fins, they work fine with the adjustable controller. I would not use one with a fixed temperature turn on, too much variance depending where you put it in the radiator.
  6. Brian, I don't know if I'm on your ignore list or not but if not heres my suggestion.

    You can use a " Capillary " type sensor probe that fit's in between the radiator coolant tubes. I like Derale and Flex-a-lite, as well as SPAL of course.

    Flex-a-lite has a nice variable speed control module set up # 31165 that has the radiator probe.

    If you just want a basic adjustable one # 31147.

    I prefer the sending unit models over the probe, but don't have a LS engine here to recommend a location, TR
  7. flynbrian48
    Joined: Mar 10, 2008
    Posts: 6,610


    "ignore list"? LOL, if I had one, I'd put LOTS of people on that one, but you're not on the list! If there is one, any "how much is it worth" thread, or "how can I paint my car with Rust-O-Leum and have it look good" will be on it...

  8. 40FordGuy
    Joined: Mar 24, 2008
    Posts: 2,907


    Another temp switch is a capillary tube style, that slips into the upper rad. hose, where it connects to the radiator. As I recall, those are adjustable.

  9. I think the ignore list is way better than the punched in the lip list. Brian does his own body work which means he has long board forearms. That is serious punch in the lip right there. :eek:

    I am thinking that variable speed fan is the way to go on an engine that is monitored for temp to regulate lead and lag and induction. I would think that keeping a steady temp is the rule of the day and a variable speed fan would really help that situation.

    Oh while I am thinking about it that bung in the radiator is for the return line for the heater, if that makes any difference how and where you rout your lines. They do make a bung that goes into the radiator top hose as well that would be worth looking into.
  10. junk yard kid
    Joined: Nov 11, 2007
    Posts: 2,720

    junk yard kid

    I got something like this but mine looks like its out of a home depot. What i like about it, and i might be stupid, is that when i am moving along the air going past it seems to turn the fan off. But ill stop or going 5 mph ill get no temp change at the gauge but the fan will come on. I speed up and it turns off.
  11. Brian, Don't know about the LS and it's water outlet but in the Stant water outlet book there is a couple of GM outlets that have a side port for a temp sender. Used one on my 348 to solve a similar issue. Most all the parts stores will let you look thru their books to see the pics for comparison. Just a thought.
  12. flynbrian48
    Joined: Mar 10, 2008
    Posts: 6,610


    Joined: Mar 12, 2006
    Posts: 263


    I've got one of the capillary tube thermostats with the adjustable relay. Summit, jegs, derale, etc all sell the same unit for under $30. My instructions said to slip it into the radiator hose, but with the thiness of the tube, I was concerned it may break someday and the bulb would wind up in the water pump. Instead, I mounted it to the fan bracket where it's touching the back of the radiator, tight to the fins. I adjusted the thermostat until I got it to turn on consistently at 200 degrees. I also have a dash switch to turn it on manually, but rarely use it. I was allittle usure the relay could handle my spal fan, so the adjustable relay controls a larger, bosch relay that is rated for way more than the fan draws.
    Joined: Jan 14, 2010
    Posts: 332


    I'm using a Dakota Digital fan controller and it is around $100. However the temp sending unit is a 1/8" NPT pipe thread. I just drilled and tapped the intake near t-stat and it works great. Maybe sending unit could be purchased seperately.
  16. flathead jack
    Joined: Aug 3, 2012
    Posts: 15

    flathead jack

    mine goes in the drain plug in the radiator
  17. gas pumper
    Joined: Aug 13, 2007
    Posts: 2,953

    gas pumper

    This is the right way to go. As long as there is airflow, almost any airflow, the fan is not needed. I find that 20-25 mph is the point where the airflow is sufficient to keep the fan off, even in 100* weather.

    Years ago I had diesels with fluid couplings driving the fan. These had an oil control valve to modulate the oil flow in the fan coupling. GM put the controler in the radiator return line. When the return water got to 160* it would turn on the fan. With a 180 thermostat these things worked great. You could not see on the gauge when the fan was running or not, that's how good it worked. You could hear the noise when the fan was fully engaged.

    I tried the under the hose sender once and wasn't happy with the seeping there that I coudn't solve without silicon sealer that looked kinda shitty.

    I have an OT CJ with a capilary tube controller in the rad core, about 3 inches down from the top. 180 t'stat and let it go to 200 (on the gauge) before the fan comes on. It cycles off and on in heavy traffic, stop and go. When moving it never goes over 180.

    Some modern front wheel drive cars with 195's let the water go to 240 before running the fan.

  18. oj
    Joined: Jul 27, 2008
    Posts: 6,247


    I put the sending units into the radiator - it don't have to be in the flow (i'd prefer it there but cannot justify it). The sending unit shouldn't go into the engine side of the thermostat because it won't shut off when you park and there is no water flow.
    Most fan controllers have an 'automatic' and 'manual or over-ride' toggle switch so you can either let the fan turn on/off by temp or you can manually turn the fan 'on' but when in manual position it won't turn it 'off' if the temp is high and you wire the relay as per the instructions were is has direct feed from the battery.
    If you put the sending unit in the block when you park the fan will continue to run (as a modern car will do) and cool the water in the radiator but the engine temp will remain high as there is no water flow and the fan will continue to run.
  19. drptop70ss
    Joined: May 31, 2010
    Posts: 1,152

    from NY

    Instead of running direct 12v I run key on 12v, that way the sending unit can be anywhere and the fan will not run when the car is turned off. I dont need a potential stuck relay failure killing the battery. My fans never turn on unless stuck in traffic for quite awhile, any air flow keeps the engine plenty cool.
  20. sdluck
    Joined: Sep 19, 2006
    Posts: 2,526


    Circle track guys use a piece of Aluminium in the top hose and it has a fitting for the sendero or temp guage.
  21. Work In Progress
    Joined: Dec 14, 2010
    Posts: 156

    Work In Progress

    Not to Hijack the thread but I mounted a capillary sender (flex-a-lite) in the fins of my 49 and when it reaches the set temp, it cycles the relay like it really doesn't want to turn on 100% then after about 10-20 seconds of that, is stops ant turns on 100%. thinking of going to a screw in block type sender with a preset temp.

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