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car wont start when hot!

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  • car wont start when hot!

    the strangest thing is going on with my car, and it only happens during the summer or warm months of the yr. i'll start my car drive around for about 30 min or less with ac on and stereo, stop the car and then when i try to start it, only makes a slight whirring sound and nothing, doesnt start. i have power, everything works but wont start. i can bump start it or jump it and it will start, or i'll have to wait till the car cools down then i can start it from the ignition. i already replaced the starter, and switched out my cables and battery, but it i still have the issue, only when its hot outside. never happens during the winter. has anyone had this issue before??

    any help would be great


  • #2
    I wonder if it could be the ignition coil? I think I have heard of this happening before when the car is hot.
    Sash K
    '88 BMW M3
    '72 BMW 3.0CS
    '04 330Xi 6-spd
    '90 Ford F-150 4WD


    • #3
      I would have guessed "Starter" but you said you already replaced that. You haven't replaced a flywheel lately have you? This just reminds me of an old problem I had once "many moons ago" on my '55 Chevy...the 265 starter didn't have the juice to crank the 327 engine when it was "hot"...but easily started it when cool.


      • #4
        When you say it "only makes a slight whirring sound" is the starter
        actually turning the engine over during this period, or is the sound the
        starter just spinning on it's own?


        • #5
          it sounds more like a electrical whirring noise, cant really tell if the solenoid is engaging in starter. the starter itself does not crank. i also replaced the coil. i spoke to some bmw dealer mechanics and theyre wondering if it is a relay, or perhaps the starter wires may be getting hot and causing a load.


          • #6
            Have you checked to see if you have power to the ECU?

            It could also be that some component has a bad solder joint that manifests only after getting up to temp.

            BTW, are you on the DFW M3 list?



            • #7
              If the engine isn't cranking over during the problem, then the problem has
              nothing to do with anything other than the start circuit.
              There's a diagnostic plug in the engine bay......

              (pic above shows someone resetting the service lights on
              a 318is but should be enough to help you identify the
              diagnostic plug)

              When you turn the ignition key to start position, power leaves the
              ignition barrel by a black/yellow wire and heads down to the starter
              solenoid to trip it in. Along the way theres a splice off it which runs
              up to pin 11 in the plug above, so you can easily check if the starter
              is getting it's trip feed. Next time the problem happens you need to
              check if there's power at pin 11 in the plug above when your turning
              the key to start. If there isn't use a fat piece of wire to jump pins
              11 and 14 together and see if she cranks over.

              Also, pull the engine earth lead off and sand both ends of it and
              where it connects to both sides.

              Originally posted by dando95 View Post
              i spoke to some bmw dealer mechanics and theyre wondering if it is a relay, or perhaps the starter wires may be getting hot and causing a load.
              There's no relays involved in the starting system other than the
              solenoid on top of the starter.

              Did you get a new starter or have your old one reconditioned?
              Was the exact same problem happening with the first starter
              Last edited by xworks; 05-23-2010, 10:32 AM.


              • #8
                I had the same problem before, the car would crank but not start when warm or hot, but would start if I bump started it.

                It turned out one of the crank sensors by the flywheel was bad. If yours does the same (still cranks when you turn the key) I would check the resistance on those to see if they're still good.
                Last edited by monzon; 05-23-2010, 05:54 PM.

                88 M3 - 04 LS430 - 03 SL500 - 95 E320 - 70 Mini Cooper
                RC Wheels by Team Pogi

                like us on facebook


                • #9
                  i did get a rebuilt bosch starter thinking i had a faulty solenoid on the old one, did not fix the problem. i will definitely check pin 11 to see if there is any power going to it next time it doesnt start. i replaced both crank sensors so that isnt the problem.

                  im not on the dfw list nick
                  Last edited by dando95; 05-24-2010, 02:48 AM.


                  • #10
                    I'm currently experiencing this issue. Car won't start when hot but I can hear a humming when I engage the key fully. After a while, the car cools down and it starts. This used to happen once a year or so but has slowly become more frequent over the past two weeks. I was thinking the starter solenoid but sounds like that might not be it. Has there been a definitive fix?
                    Last edited by Brandon; 07-15-2016, 08:10 AM.
                    Alles Beste!

                    B. Wheaton
                    1989 E30 M3, Owner since June 2000
                    2008 E61 535xiT - The DD and work horse


                    Register your E30 M3!


                    • #11
                      yes, we can trade cars. mine starts everytime...if i remember to keep it on the charger between drives.

                      heat can change the resistence in copper wires, so you could have an issue with the usual suspects:
                      -ignition coil
                      -flywheel sensors
                      -alternator wiring (power or grounds)


                      • #12
                        Just as an fyi, I had a similar issue on my early production M3 (foggy memory as this was 10yrs ago...).

                        I don't know if all cars have this, but near the battery the second largest wire going from the positive terminal had a 50A fuse. Since the OE part was not a replaceable fuse (it was soldered) as things got warmer, the car would not start. See item 14 here:


                        It will be hidden under some factory tape and under the plastic protective cover (item 12 above) a few inches behind the battery connector in the trunk.


                        • #13
                          I have this issue also. It's become progressively worse over the past 6 months, to where i pretty much know it wont start after a drive of more than 20 minutes.
                          I have a voltmeter setup, and just recon'd the alternator with new voltage regulator, bushes and belt. I get 12.2v from the battery under idle without any draw. Once i've been up to 3500rpm, i have 13.9 / 14v
                          I have a new battery 75amp, with 760 start amps so battery is not the issue.
                          i doubt the alternator is either
                          But i found a post from a member "Mags" from 2004
                          And it sounds exactly like the issue we have

                          * no starter activity when warm
                          * electric buzzing sound, almost like fuel pump under priming
                          * lights DO NOT go out when activating solonoid.

                          I did experience a couple of episodes of the pinion spinning without engaging, and think this could be the solonoid is weak.
                          Others comented that the engine is braking the starter.

                          1) can ALWAYS bumpstart
                          2) start using jumper cables ALWAYS works.

                          A battery booster does not seem to help..

                          I've not yet done the pin 11 to 14 on the obd plug yet,

                          I think it's the starter?
                          Please share your opinions
                          I thank god for every day i'm on this earth,
                          with an E30M3


                          • #14
                            Link to the thread from Mags

                            I thank god for every day i'm on this earth,
                            with an E30M3


                            • #15
                              I have this same problem, though it's intermittent. Usually the car will start immediately after I let it sit for 15-30 min without touching it. Sometimes the car starts immediately if I turn it off and turn it back on. No idea WTF the problem is, but I'm cautious to always park where I can coast down a hill and pop the clutch if need be. I bought a starter, but I haven't replaced it yet. The engine is about to be removed for a head gasket (and so I can get OCD on the engine bay and block). While I'm in there, I'll replace all of the relays and whatever other electro-magical components could be culprits.

                              Here's a video of my issue on the FB group.

                              Alles Beste!

                              B. Wheaton
                              1989 E30 M3, Owner since June 2000
                              2008 E61 535xiT - The DD and work horse


                              Register your E30 M3!