Real time temperature measurements anywhere - engine, trans, PS, exhaust etc - cheap!

Discussion in '80-Series Tech' started by e9999, Jul 23, 2005.

  1. e9999

    e9999 You want to do what...? Moderator

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    OK, all this talk about coolant temperatures made me curious about my engine so I just put together a trivial little system to check the coolant temp but I can also measure temperature just about anywhere: coolant, engine, exhaust, PS, engine bay, radiator, anywhere you can stick something.

    Here is what I did:

    I happened to have a multimeter that can read temperatures. This is done with a thermocouple probe you just stick in the multimeter inputs as if it were a voltage measurement (it is of course). This approach will work also with a dedicated thermocouple digital thermometer/display. You can buy one of these from www.omega.com for $65. The approach may or may not work with a home inside/outside air thermometer ($30) because the temp ranges for those is much narrower, so you'd have to check the max temp it can read. With a K thermocouple I can go from well below freezing to 1300C (better not get there)! This will also work with other types of thermocouples. An E type might be more sensitive but slightly smaller range I think and more costly displays IIRC.

    I scrounged a 10' length of scrap K thermocouple wire. ($5 or so new). I made a bead simply by soldering the 2 wires with a common soldering iron and regular solder. I tried the thermocouple in boiling water and got 99.9C (!) Not bad. You can buy all sorts of thermocouple probes premade, including flat ones, bolt ons etc, but more costly of course.

    Then I just stuck the wire through the grommet above the brake pedal into the engine bay. Pulled it out into the bay. Took a hose clamp and a piece of rubber hose. I put the hose clamp around the metal pipe going from the DS side of the head to the top radiator hose, the one with the flat that some guys here used to drill and tap for an inside gauge. Then stuck the rubber between the clamp and the pipe, and finally stuck the thermocouple bead under the rubber against the metal. Tightened it all up. Then I just plugged the thermocouple wire in the multimeter inside the cab and that's it. I can read the temperature of the coolant pipe from inside the cab. No drill and tap or use an adapter into the coolant hose, no need for a dedicated temp gauge to be stuck in the dash or pillar etc.

    Now admittedly, that is not the temperature inside the coolant itself but I'm pretty sure it's very close, I would say within 5F or likely less, guessing, because it's a metal pipe and the bead is insulated with 1/4" of rubber. It would normally be a tad colder than the solvent, but it may pick up a tad of extra heat from the head metal. I am confident it's reasonably close (See another post I'm going to start on coolant measurements that confirms that.) Also, I put it towards the back of the pipe so it's not exposed to the fan air flow. Doesn't matter that much cuz a measurement like that will vary depending on where exactly you measure anyway, and is best used on a relative basis to look for unusual overheating. It would be the same with anything else, you'll always get the surface temperature, but it should be close if you do it right. You can also use thermal grease on the bead if you want faster response and slightly more accurate readings. I didn't bother.

    The point, though, is that I can now put this thermocouple anywhere I want. I can stick it under a bolt, put it on with duct tape, can leave it hanging if I want the engine bay air temperature, stick it on the exhaust with a clamp, on the PS reservoir with a rubber band :) , whatever. It can be stuck on with epoxy if I want to do that. You can stick it into the A/C vents to check your air temp. You could stick it on the head at various places to see if you have a hot spot. Use it to check your fridge temp, or see if you have a fever (you test that one... :D) Whatever. Uses a battery, no need for power. Very versatile.

    For a few $ more you can get a display that can handle 2 separate thermocouples, so you could do coolant and trans at the same time. You can also record the max and min and avg temp you got, set up an alarm for overheating etc...

    And darn cheap:
    Digital temp display: $65 (or $85 with high temp alarm; or multimeter with temp reading $125)
    Thermocouple wire: $5
    Thermocouple connector: $5.
    1 hour time

    HTH! Enjoy!
    E
     
  2. MH_Stevens

    MH_Stevens

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    e9999....... So have you backed off the OBDII to PDA as the best choice?

    Why the change when OBDII to PDA give multiple data on one screen? I realised I can install a multimedia DVD screen to which I can output the data. Have you measured your real-time delay with such a long thermocouple wire? Time is of the essence when the HG is about to blow!
     
  3. acolella

    acolella

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    If I keep hearing this HG thing, I think I'm about to blow my head gasket!!! :mad:
     
  4. e9999

    e9999 You want to do what...? Moderator

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    nope, I'll still do the laptop bit likely (not PDA though probably) later on. But I could do this at zero cost and in less than one hour. And this is more versatile in some ways (not all) although of course you don't have access to some interesting data like timing etc...
     
  5. e9999

    e9999 You want to do what...? Moderator

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    may try the trans temp next. Which one of the 2 ATF lines to the cooler is the hot one, if anybody knows off hand?
     
  6. Lars

    Lars

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    How about taking temp measurement on the timing chain cover? Or oil temp?
     
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