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Is my M20 overheating?

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    Is my M20 overheating?

    Silly question, I know. Bear with me.

    Symptom 1: I'm driving on the highway, and out of nowhere the temp gauge jumps up to full red within an instant. It then goes back down to normal, and bounces around a bit...back and forth between normal and super high, very erratically. This, to me, seemed to be clean-cut sender or gauge issue.

    Symptom 2: Symptom 1 goes away and turns into sustained temp that's not in the red, but definitely above normal...though with moments where the needle jumps down to normal immediately, then right back up to being too hot.

    Symptom 3: Now i've stopped driving the car, because the temp gauge will gradually go up, and stay steady, a little bit under the red. No more jumping around erratically.

    I put a new sender in. No change. There's no noise from the water pump. The mechanical fan works fine. The electric fan is NOT kicking on with the car idling and the temp reading high (both low and high switches are new, as is the resistor). The t-stat seems to be opening fine.

    Temps read with an infared thermometer:
    135-140º on the heater hoses (both sides of the t-stat are about the same).
    180-185º on the thermostat housing.

    I know there are some insulating properties to the hoses and t-stat housing. But a reading near the red should mean that the temp is 250º or above, I would presume. Readings of 185º max seems a bit low for something that's supposedly overheating. The electric fan should kick on if it's overheating.

    Thoughts? At first, it seemed electrical. But the gauge behavior is acting legit now. However, the infared thermometer readings and electric fan behavior don't support it.
    -Nick
    sigpic
    1986 325es || 1998 M3 sedan || 2003 330ci

    ~Looking for a left side early tail light, or a set of early tails~

    #2
    have you bled your cooling system? jack up drivers front side, start car, turn heater on full blast, let it warm up then open/loosen (not remove) bleeder valve on top of thermostat housing. let it bleed out air pockets. rev engine through this process too.
    sigpic

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      #3
      pull the gauge, check the nut and contacts. faulty connections can offset the needle position in my experience
      89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

      new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

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        #4
        mine does this as well, i assumed it was the si board or a sensor issue. I have not looked into it yet.

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          #5
          Originally posted by digger View Post
          pull the gauge, check the nut and contacts. faulty connections can offset the needle position in my experience
          Definitely go this route first. Would have been much less of a headache chasing my cooling system issues.
          Originally posted by StereoInstaller1
          Do you feel like something is trying to penetrate your butthole?

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            #6
            My stock gauge also likes to jump around sometimes. It also will read high without jumping, tricking me into thinking the car is running hot.
            When I have the cluster out for something else, I'll check the grounds to try and get it working. I'm in no rush, because...


            I decided to upgrade to something more accurate and reliable.
            I've only had it in there for about a month, and it's already notified me of a pinhole coolant leak I had.
            $50 well spent IMO.



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              #7
              rite after i did my M50 swap i was having the same issues, sometimes the gauge never moves from dead center sometimes it creeps up to red and sometimes it flickers.. whenever it would creep up i would pull over and check all the temps of everything with a laser temp gauge thing (with the car still running) and nothing would be above 205*.. anywhere.. so i just blamed it on the gauge and ive been driving it for almost a year like that..
              IG: haggardfab

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