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Strange fan/temp issue with my cooling system

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    Strange fan/temp issue with my cooling system

    So on my swap (NV M50, M42 radiator, SPAL electric fan), my electric fan stopped coming on. I was using the old M20 radiator fan/temp switch in the M42 radiator (the 2 prong spade-connector type), and it was working fine. Then the fan stopped working, so we replaced it with the 3 prong from a Z3 1.9, same one GPS uses on all their cars. New switch/sensor, and wiring leads. Got it all hooked up, and the fan still isn't coming on.

    We jumped the wiring leads, and the fan does work. Both the main radiator hoses on each end are getting good and hot, and the gauge is going all the way to the red before we shut the engine down. Coolant is flowing through the radiator.

    Another thing I noticed was the temp gauge in the dash didn't start to read until the car had been on and running for about 10 minutes, it sat completely dead. Then the needle suddenly jumped to just over 3/4, and started to climb normally to about 1/2. It sat there for a bit, then dropped down to just a hair under 1/2, and then climbed steadily until it got to the red, and then we shut it down. Still no fan.

    Our suspicion is that *maybe* the needle on the temp gauge is off by about a 1/4 (since I took it off at some point long ago to paint it), and that's why it's taking a good 10 minutes or so before it starts to read anything. But it seemed to work normally before, which is what's puzzling. Tomorrow, we're going to check the radiator temps with a laser temp gun, and see what temps it's actually running at.

    Does anyone have or know of something that will tell me what temp the cooling system should be in relation to where the needle sits on the gauge? If I could find out what temp the cooling system is at in relation to where the needle is reading, I could find out if I have the needle off by about 1/4 or so.

    #2
    Have you tested direct power to the fan?

    Nevermind, I read the second paragraph.

    Comment


      #3
      Had this exact same problem buttoning up my swap, had to replace my connector because the pins had shitty contacts.

      Also, an air bubble trapped in the rad where the switch is (or being low) can cause this.

      Comment


        #4
        It's a brand new switch, connector and contacts.

        Andrew did say that he thought that particular corner of the radiator didn't feel as warm as the other parts. We're going to check it tomorrow with a laser temp gun. That almost seems more likely, I dont think the gauge is wrong, but I can't say for sure.

        Comment


          #5
          I have something similar to this.



          It has saved me a lot of cooling system bleed headaches.

          Comment


            #6
            BMW temp gauges generally read at the dead center of the gauge when they're at normal operating temperature. IIRC that should be about 180F. My gauge always reads a few ticks under that when cruising. I think it may be due to my triple core rad.

            Did you try throwing another cluster in there to see if that fixes the wonky gauge issues?
            Last edited by AnimalE30; 06-23-2012, 11:53 PM.

            Comment


              #7
              I don't have another cluster to check it, but this is all made even more strange by the fact that all of this worked fine before I yanked the engine last winter. Temp gauge worked fine, and so did the fan. NO wiring changes were made.

              Comment


                #8
                I fixed it, there was just a bubble in the radiator still where the temp switch/sensor threads in. When we pulled the first one out, not a drip. And even yesterday, after we heated the car up and the fan still wasn't coming on, still nothing out of the hole.

                So I jacked the car up on the driver's side just now, and ran it until it got hot, and bled the system one more time. Gave the hoses and bunch of good squeezes, whacked that side of the radiator with a rubber mallet a few times ( :D ), and after a few good bleeds, got the fan coming on at just over half. Took it out for a good flog, pulled it back in the garage on flat ground, and it came right on again.

                Good ol' M42 radiator! It's funny, I had NO trouble bleeding it the first time I put it in, guess I just got lucky! :up:

                Comment


                  #9
                  Hahaha that's some E30 logic right there. Glad you got it sorted man.

                  Comment


                    #10
                    Originally posted by Janderson View Post
                    I fixed it, there was just a bubble in the radiator still where the temp switch/sensor threads in. When we pulled the first one out, not a drip. And even yesterday, after we heated the car up and the fan still wasn't coming on, still nothing out of the hole.

                    So I jacked the car up on the driver's side just now, and ran it until it got hot, and bled the system one more time. Gave the hoses and bunch of good squeezes, whacked that side of the radiator with a rubber mallet a few times ( :D ), and after a few good bleeds, got the fan coming on at just over half. Took it out for a good flog, pulled it back in the garage on flat ground, and it came right on again.

                    Good ol' M42 radiator! It's funny, I had NO trouble bleeding it the first time I put it in, guess I just got lucky! :up:
                    Originally posted by RobertK View Post
                    Also, an air bubble trapped in the rad where the switch is (or being low) can cause this.
                    Good Call

                    Originally posted by Roysneon
                    $5 shipped?
                    Originally posted by MarkD
                    You are a strange dude, I'n not answering any more posts from you.

                    Comment


                      #11
                      Glad to hear you got it sorted. I hate cooling system issues. They make me a nervous wreck.

                      I found that bleeding on an upward incline with the expansion tank cap off always seems to remedy air bubble issues.

                      Comment


                        #12
                        Originally posted by RobertK View Post
                        Glad to hear you got it sorted. I hate cooling system issues. They make me a nervous wreck.
                        Me too. But you totally called it!

                        Comment

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