Can I use the block drain for a temp sender?

Heating / Cooling / AC

  1. YY1

    YY1 Well-Known Member

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    I'd like to keep the factory gauge but install an aftermarket one that actually indicates the temp.

    There is a threaded hole near the pass side oil pan rail that I believe is the block drain.

    Can I use this?

    It would also help hide the big, shiny spring encased sender lead in my otherwise stock engine bay.

    I can't seem to find any info online about what the difference in temp might be between the water in the top of the engine and the bottom.
     
  2. hunt2elk

    hunt2elk Well-Known Member

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    I tried it on a small block a few years ago, and couldn't get it to work. Not sure if there isn't much flow down there?
     
  3. Plymouth 65

    Plymouth 65 Floorable Deplorable

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    I have the same question. I don't see an issue with it because once the engine warm up the temperature should normalize. 65'
     
  4. RedFish

    RedFish Well-Known Member

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    I guess the first question is, is there a well/cavity there. Temp senders do have a probe end reaching into the water. Some aftermarket temp senders are too long for the correct intake location.
    Of course the water would be hotter there, like oral thermometer versus rectal thermometer. OEM temp sender reports a general/average water temp. The water jackets around cylinders would read significantly hotter.
     
  5. Max1196

    Max1196 Well-Known Member

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    Block drain at bottom = not a good location to get an accurate temp reading, select somewhere up near the t-stat.
     
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    • jazak5

      jazak5 Well-Known Member

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      like oral thermometer versus rectal thermometer.
      probe end reaching

      easy:poke:
       
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      • toolmanmike

        toolmanmike Moderator Staff Member FABO Gold Member

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        Most of the block drains are full of casting sand. Not a real good place for a sender.
         
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        • SGBARRACUDA

          SGBARRACUDA ROY FABO Gold Member

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          This is kinda related. I install radiator petcock fittings in both of those locations. (One on each side of the block). Then when ever you are pulling the intake or the heads, you won't have water/antifreeze running every where like the intake valley or cylinders. If you open these drains before you start taking your engine apart. Much cleaner, less messy.
           
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          • draginmopars

            draginmopars Well-Known Member

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            I also do that on all engines.
            makes prepping race engines for winter easier,
            then in the spring, drain the antifreeze
             
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            • Alaskan_TA

              Alaskan_TA Well-Known Member

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              I have installed a pipe T for this in the past. Original sender at top & the thermal sender in the side port.

              This also works if wanting to keep your original oil sender gauge & want to add a gauge showing the actual PSI.
               
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              • chryslerfat

                chryslerfat Well-Known Member

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                All of the old Oliver farm tractors are set up this way because they didnt have anti-freeze back then and used alcohol in the winter.
                 
              • Dfr360cuda

                Dfr360cuda Diagnosis... Plum Crazy.

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                .........................

                Q... What's the difference between an oral and an anal thermometer ?

                A... Taste
                 
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                • 67Dart273

                  67Dart273 FABO Gold Member FABO Gold Member

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                  If your sender is small, like 1/8--1/4" pipe, I've thought about drilling and tapping one of the rear intake manifold "blanks" where they cover the water ports in the rear end of the heads.

                  doubt you want to do that for a mechanical gauge, although "I guess" you can buy 3/8" pipe adapters for them
                   
                • krazykuda

                  krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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                  Are we still talkin' engine blocks here???
                   
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                  • krazykuda

                    krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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                    A nurse reaches into her pocket and pulls out a rectal themometer and says, "Some @sshole has my pen".... :BangHead:
                     
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                    • draginmopars

                      draginmopars Well-Known Member

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                      I hit like, then changed my mind> it didn't seem right...lol
                       
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                      • BillGrissom

                        BillGrissom Well-Known Member

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                        The block drain is at the bottom of a V-cavity, so it isn't very deep there, just enough clearance for the plug. When you remove it, coolant usually doesn't flow out until you break up the rust crud w/ a screwdriver. A stagnant area which won't measure typical coolant temperature. For sure don't screw one in, bottom out, and strip the threads or crack the block. The plug is 1/8" NPT in a V-8 (one on each side) and 3/8" NPT in a slant (single).
                         
                      • Tooljunkie

                        Tooljunkie King of cobble/master of the broken bolt FABO Gold Member

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                        V8,1/4” npt. Just had mine out.
                         
                      • superchargeddrt

                        superchargeddrt Well-Known Member

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                        I've seen water necks for thermostats with a extra NPT hole in them.
                         
                      • famous bob

                        famous bob mopar misfit

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                        ^^^^^
                        THIS. I GOT 1/4" DRAIN COCKS IN MINE TOO.
                         
                      • 67Dart273

                        67Dart273 FABO Gold Member FABO Gold Member

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                      • BillGrissom

                        BillGrissom Well-Known Member

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                        Correct, sorry for the mis-info. In all my cars, I installed a knock sensor in the drain holes, from a 85-95 Chevy V-8 (as GM did). Fits directly in the SB & BB drain, needed a 1/4 to 3/8 NPT bushing for my slant. The GM knock module can send a "I'm knocking" signal to an engine controller (ex. Holley Commander 950), which retards the spark.
                         
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                        • MRGTX

                          MRGTX Well-Known Member

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                          :D :D
                          Please tell us that you didn't figure this out based on research. LOL.
                           
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                          • JoeSBP

                            JoeSBP RLTW!

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                            Interesting. Is there a thread on this? can the sensors function stand alone like just a warning light?
                             
                          • BillGrissom

                            BillGrissom Well-Known Member

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                            I would think so. The GM knock sensor is just 1-wire (blue) which runs up to the knock module on a bracket on the intake manifold. Sig- is ground. You can find wiring diagram for the module (try Megasquirt site). As I recall, it outputs an on/off 5 V signal that is high when sensing knock. I plan to use w/ a Holley Commander 950, but no reason you couldn't just light a dash LED. The sensor is just a piezo-electric quartz crystal (like a "crystal" microphone), presumably with a weight tuned to resonate when the engine is knocking. Some have to tried to figure out the various GM PN's and worry if a six cyl or even Mopar/Ford V-8 would sense the same. I recall the conclusion is that GM used the same PN for V-6 and V-8 and they just varied by year or whatever, so "should work". They are all push-rod engines, so should sound similar. Holley's algorithm just keeps increasing the spark (within limits) until it senses knock, immediately jumps back ~2 deg, then starts creeping up again. I expect most factory engine controllers did similar, so it is always finding the sweet spot for any cheap gas you put in your ride. SAE papers I read in the early 1980's (when developing such) said a little knock actually improved combustion (efficiency and power). By the time the driver hears pinging, it isn't "minor". Thus, I expect they are designed to always allow knock just below a threshold.

                            While picking GM, grab the 8-pin HEI module inside the "small cap" distributor, the pickup cable (snip), unplug the cable to the coil, grab the coil and power/tach cable (snip). You can connect the module to a Mopar e-distributor pickup (2 ways, only 1 sparks best). TrailBeast here kits those parts (HEI, not knock) if willing to pay a lot more to avoid a junkyard.
                             
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