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Thread: M62 Coolant Temperature Sensor

  1. #1
    Join Date
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    M62 Coolant Temperature Sensor

    Good evening everyone. So I've been trying to get in to see this mechanic who is booked months and months and months out. I've had a problem with rough starts, stalling and an intermittent sudden complete loss of power on my E39 M62 build date 2/9
    After several tries of trying to get in to see this mechanic I finally just told him the symptoms on the phone today and he asked me when was the last time the coolant sensor was changed? I responded that I didn't know but the temp gauge was standing straight up and down every time this happened. He replied with no not the one in the cluster the one that talks to the computer.
    So my question is where is this coolant temp sensor located?
    Where do I get the real OEM number for it from, what diagram? And lastly, is it a relatively easy DIY that I can do myself? Thank you as always all in advance.

    Sent from my SAMSUNG-SM-G935A using Tapatalk

  2. #2
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    https://www.realoem.com/bmw/enUS/sho...diagId=11_7489

    The "dual temp switch" aka "dual temp sensor" lives in the top of the water pump housing. This single sensor has 4 wires, and according to the wiring diagrams, two separate thermistors, one to feed the DME, one to feed the cluster.

    So it IS possible that the DME is reading a different value than the cluster.

    That said, I doubt that's your issue. Still, if you want to check that, you read live data for coolant temp through the DME, and through the cluster, with a good BMW scan tool....

    The separate sensors ended in the previous generation.

    Personally, I'd be looking at fuel/air issues, but I'd absolutely start by connecting the car to a top quality BMW scan tool, reading codes, and watching live data, to look for an anomaly. Likely also a smoke test, since the M62 leaks like a sieve.

    You can't fix it until you know what's broken.

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

  3. #3
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    I can think of a half dozen things it 'could' be but the dual temp sensor is not one of them. This is not an engine you want to throw parts at. As Chris stated, get a proper diagnosis. You'll be money ahead in the long run.

  4. #4
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    Quote Originally Posted by bmwdirtracer View Post
    https://www.realoem.com/bmw/enUS/sho...diagId=11_7489

    The "dual temp switch" aka "dual temp sensor" lives in the top of the water pump housing. This single sensor has 4 wires, and according to the wiring diagrams, two separate thermistors, one to feed the DME, one to feed the cluster.

    So it IS possible that the DME is reading a different value than the cluster.

    That said, I doubt that's your issue. Still, if you want to check that, you read live data for coolant temp through the DME, and through the cluster, with a good BMW scan tool....

    The separate sensors ended in the previous generation.

    Personally, I'd be looking at fuel/air issues, but I'd absolutely start by connecting the car to a top quality BMW scan tool, reading codes, and watching live data, to look for an anomaly. Likely also a smoke test, since the M62 leaks like a sieve.

    You can't fix it until you know what's broken.
    Thanks for this. These where my thoughts all along before I spoke to the mechanic. In fact my call to him before I found out he was booked for months, was to get a smoke test.
    To that end, could you expand upon that a little bit in detail as far as the M62's "leak like a sieve" goes please? Thanks again.

    Sent from my SAMSUNG-SM-G935A using Tapatalk

  5. #5
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    Try www.bimrs.org to find an independent shop that specializes in bimmers in your area. A reputable shop can perform a smoke test without much problem. However, the first step in diagnosing a problem is to scan the engine computer (DME) and the automatic transmission computer (EGS) for codes. Throwing parts at a problem wastes money, doesn’t fix the problem and it angers the BMW goddesses. Scan first!

  6. #6
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    Quote Originally Posted by MarcoZandrini View Post
    Try www.bimrs.org to find an independent shop that specializes in bimmers in your area. A reputable shop can perform a smoke test without much problem. However, the first step in diagnosing a problem is to scan the engine computer (DME) and the automatic transmission computer (EGS) for codes. Throwing parts at a problem wastes money, doesn’t fix the problem and it angers the BMW goddesses. Scan first!
    I hear ya! Thanks.

    Sent from my SAMSUNG-SM-G935A using Tapatalk

  7. #7
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    "Leaks like a sieve"..... yeah, sure, I'll explain.

    Air: The intake elbow o-rings leak. The o-rings / seals for the front and rear manifold covers are practically famous for leaking. All the vacuum fittings on the rear manifold cover are prone to leaking. The Pipe from the front Oil Separator to the rear manifold cover leaks. The front oil separator has a plastic "L" fitting that shatters, and leaks. And well, then there's all the intake manifold gaskets and injector seals, which thankfully really only leak if you mess with them.

    Coolant: Do you really want me to go there? Rear water manifold gaskets, the o-rings at either end of the under-manifold pipes, the cover plate on the rear of the engine block inside the bellhousing, EVERY plastic cooling system part. The valley pan.

    Oil: Lower oil pan gasket, upper oil pan gasket, timing cover gaskets, the seals between the cylinder heads/ block and the timing cover. The vanos solenoid seals (oh, yours is a '98, never mind them.)


    AND, just so you know, I think this is a great engine, although I'm very partial to the TU, which also leaks like a sieve.

    Of course, I do have a friend / racer / instructor, who's put an S62 and 6 speed in his E38 740....that's even better.....

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

  8. #8
    Join Date
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    '98 540i '01 540i 13 E70
    Quote Originally Posted by bmwdirtracer View Post
    "Leaks like a sieve"..... yeah, sure, I'll explain.

    Air: The intake elbow o-rings leak. The o-rings / seals for the front and rear manifold covers are practically famous for leaking. All the vacuum fittings on the rear manifold cover are prone to leaking. The Pipe from the front Oil Separator to the rear manifold cover leaks. The front oil separator has a plastic "L" fitting that shatters, and leaks. And well, then there's all the intake manifold gaskets and injector seals, which thankfully really only leak if you mess with them.

    Coolant: Do you really want me to go there? Rear water manifold gaskets, the o-rings at either end of the under-manifold pipes, the cover plate on the rear of the engine block inside the bellhousing, EVERY plastic cooling system part. The valley pan.

    Oil: Lower oil pan gasket, upper oil pan gasket, timing cover gaskets, the seals between the cylinder heads/ block and the timing cover. The vanos solenoid seals (oh, yours is a '98, never mind them.)


    AND, just so you know, I think this is a great engine, although I'm very partial to the TU, which also leaks like a sieve.

    Of course, I do have a friend / racer / instructor, who's put an S62 and 6 speed in his E38 740....that's even better.....
    Oh man, WOW! Until I got to the "AND, just so you know, I think this is a great engine" part, I was thinking how much I love this engine and driving this car when she's standing tall. I did buy her with 295K and blown transmission as a project car and the more I was around her, and tinkered with her fixing this and that from finding out information on here from all you guys, the more I liked the car. I should say it's the first one I've ever owned, and I'm a old school headers, high-rises, carburetors and distributor caps where you use points and can diagnose an electrical leak by looking for sparks under the hood at night... after I got the transmission fixed, I was amazed absolutely amazed at how this car performed on the highway. Anyway, this is great information to know for future reference, and also after I get a smoke test and a proper scan, to start thinking about replacing should they need to be replaced, providing I'm going to keep the car and it's cost-effective of course. S62 in an e38 huh? Very interesting.
    Reminds me when I pulled a 318 out of a roadrunner and put a 340 in it...
    Thanks for all your help man much appreciated!

    Sent from my SAMSUNG-SM-G935A using Tapatalk

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