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  1. #1
    RC poster
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    Aug 2013
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    Temp sensor showing too hot... and speed sensor may be incorrect?

    Ive recently installed the temp/volt sensor and the speed/rpm sensor on my new Revo 3.3 truck.
    The problem is that the temp sensor is showing that the engine is too hot, when the engine is cold and i
    start it up it takes like 10 seconds before its showing about 300-320 fahrenheit. The engine is set quite
    rich on fuel mixture so i can only think of a faulty temp sensor. The volt sensor works fine. Ive installed
    the sensor around the bottom of the cooling head. What is the ideal temp of the 3.3 engine and what can
    be wrong?

    Also the speed sensor showing that the car is running at 12 mph when in idle and when the car is standing still.
    Is that normal or is anything wrong here too?

  2. #2
    RC Champion
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    Feb 2013
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    Parker, CO
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    1,390
    the speed sensor reads off of the crank shaft, so if the motor is running it's going to show a mph speed, even if you are not moving. it's not reading the driveshafts or wheels. it's kind of hokey.

    the temp sensor needs to be positioned so that the little sensor bulb that is in the long black loop wire is situated on either side of the exhaust port. If it's on the port then you will get an elevated temp reading. honestly - toss it in the trash.
    I have an RC problem...

  3. #3
    RC Qualifier
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    Jun 2007
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    Farmingville, NY
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    682
    I was wondering the same thing about the temp. I bought a brand new truck with them factory installed and I also feel like it reads too hot.. although before I start the truck the temperature does read the ambient temperature about correctly.
    Traxxas please sell kits!

  4. #4
    Marshal Double G's Avatar
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    May 2008
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    I've said it multiple times that the on-board gauge is accurate for taking the temp and it will read the temp where the sensor is. HOWEVER, the true temp of the engine should be taken at the glow plug so you could take the temp at the glow plug and compare to the on-board and see the difference and take that into account each time you look at the telemetry or you could try to position the on-board so that the two are closer together.
    The Super Derecho

  5. #5
    RC poster
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    Aug 2013
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    Ok I will try to place the tempsensor closer to the glow plug and check if the temperature shows a more accurate reading. If not i will do as rock-rod said, toss it in the trash.

    But will the speed sensor show a accurate reading while driving or is that sensor edit too?
    Last edited by Double G; 08-17-2013 at 04:33 PM. Reason: language

  6. #6
    RC Qualifier
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    Jan 2013
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    Gurley, Alabama
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    Put the sensor in between the 1st and 2nd cooling fins on the bottom of the head. Center them between the exhaust and carb. DoubleG meant check the temp at the glow plug (with an infrared hand held temp sensor)and compare that number with what the on board number is. Then adjust the on board sensor either closer to or farther from the exhaust, depending on the difference in the numbers. Once you get it dialed in it should be as reliable as anything else. But you will want to keep an eye on it every now and then with a hand held sensor just to be sure the on board sensor hasn't moved on the head and is still being accurate. If the wire is either to tight or to loose on the head it will read inaccurately.

  7. #7
    RC Turnbuckle Jr. fallonguy's Avatar
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    May 2006
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    Dayton Nv.
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    3,182
    You will never be able to get a true speed from the flywheel because of the 2 speed transmission and because the tires balloon when you're at high speed. As for the temp I moved my sensor around until I found a place that was close to the temp from my temp gun.
    I wanted to put a really cool signature but I ran

  8. #8
    RC poster
    Join Date
    Aug 2014
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    18
    It's accurate. Any contact temp device is more accurate than non contact. It's touching it lol. I've found with the 3.3 especially that using a gun aiming at the glow plug is not that accurate. You'll always find it hotter if you hit the engine sideways at an angle towards the bottom cooling fun on the head. Try it out. The hotter it runs the more difference you'll see between there and the glow plug.

    Glow engines can withstand 300s just fine as long as you not lean. You want it to be minimum of around 220. If you are measuring 250 at the glow plug with an infrared your most likely running a true 280 or so. Put the sensor at right above the piston where it should be and forget your stupid temp gun. Tune for performance slightly rich and use your telemetry as a gauge. Get used to the hotter reading because there's no reason for it to not be accurate. As long as its consistent.

    If 270 to 290 is where it runs on a hot day so be it. What you gonna feel better cause a temp gun reads lower even if it's not nearly as accurate?

    So now when it runs 330 then maybe you can be concerned because it never normally reads that. That's just an example.

    Always go by if your rich or lean. You never richen more if it's already rich because a temp gun gave you a number

  9. #9
    RC Racer
    Join Date
    May 2017
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    244
    IMO, get rid of that telemetry garbage. When I rebuild my engine, I'm going to take the temp and rpm sensor out... Less wires=cleaner setup and less to go wrong. I never found the temp sensor to be that accurate. The rpm sensor is OK but since the app uses rpm to calculate speed, it's not accurate at all. Especially because of the 2 speed transmission and the tires ballooning at high speeds.

    If I'm concerned about my temps, I'll use a temp gun, but 95% of the time I don't bother checking my temps. If I see smoke coming off of the glow plug, I'll let it cool for a bit.
    Slash 4x4 w/TSM
    Revo 3.3

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