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Thread: Temperature gauge spike then drop to normal

  1. #1
    Join Date
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    Temperature gauge spike then drop to normal

    Hi all.

    2004, 318i.

    This morning while driving to work, I suddenly noticed my temperature gauge in the red as I was pulling up at a set of lights. I switched the engine off immediately and waited for the lights to change. I was planning on starting it back up and driving around the corner and turning it off but after starting it and driving for a few hundred meters it dropped to about 10 o'clock then jumped around a bit before settling in the normal 12 o'clock position. I pulled up anyway and checked for signs of over-heating but it seemed fine. Top hose hot, bottom cold. So continued on to work with no issue.

    About 4 days ago as I was driving I just glimpsed it falling back into the 12 o'clock position from above really rapidly but thought my eyes were playing tricks on me because of the speed it fell at.
    In the time since that first instance and this morning I have driven around 500kms and not had any issues.

    After getting to work and letting it cool down, I checked and my coolant levels are normal. I was thinking of checking if there was any air bubbles by bleeding it but need to get some coolant after work this afternoon (I'm at work now).
    What would be the most likely cause of an intermittent spike in temperature reading that drops quickly back to normal?

    Cheers.
    Last edited by MilesWilliams; 05-30-2018 at 10:22 PM.

  2. #2
    Join Date
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    Your thermostat might be sticking on the closed side or your fan clutch might not engage (in case of mechanical fan) or the fan might not be switching on (in case of electric fan).

    Regarding air bubbles: is your interior heating working properly?

    Switching off your engine when it gets hot is not necessarily the best thing to do, by the way, since the coolant will stop flowing and the hotter engine block will heat up the coolant causing it to expand. Sometimes, when there is no sign of a coolant leak or steam but i.e. your fan is not working, the better action is to turn your interior heater up to maximum and driving off under light load so the coolant can circulate and get rid of the heat.

  3. #3
    Join Date
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    Ok.
    Thanks for the info regarding the heater.
    Haven't had a chance to check if heater is working.

    A small update though to provide as much info as I can. Drove home from work just now, keeping an eye on the temp for the whole 120km trip and it was sitting at 12 o'clock for the whole trip except for one instance a few minutes into the beginning of the trip where I watched it spike into the red and fall back into the normal position within 1to 2 seconds. The speed at which it spiked and fell makes me think it's not actually overheating but that the instrumentation is getting a faulty reading or it's an issue with the instrument cluster.
    If my thermostat was sticking, I'm assuming the needle would gradually increase, not spike as fast as it could and then drop at the same rate?

    Any other suggestions would be greatly appreciated.

    Cheers.

  4. #4
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    Another quick update.

    Driving to work this morning, again, 120km trip where I kept an eye on the needle the whole trip, and again, a few minutes into the trip it spiked and fell to normal, twice this time. I noticed though, (and I saw this yesterday on my way home) that before spiking, it dropped just slightly below the 12 o'clock for a moment and then shot up towards the red and back to normal within a second, maybe a second and a half.

    In regards to the heater, I checked it this morning and yes it was blowing hot air. I have never actually used the heater before, I am in Australia and it doesn't really get cold enough here to warrant using the heater where I am, so I'm not sure if this is normal, but no hot air comes out of the vents on the dash, they blow cold, but the legs and the windscreen ones were definitely blowing hot, actually hot enough to make me start to sweat within a minute or two. Should my dash vents be blowing hot air or are they designed to only blow cold? Do they only pull in air from the outside through the microfilter?

    I am pretty sure the fan is engaging. Although my commute to and from work is mostly freeway driving, yesterday there was an accident and I crawled for about 15-20 minutes at less than 15km/h, sometimes slow enough that the speedometer didn't move, and even came to complete stops. If my fan wasn't engaging, it would have definitely over-heated with no air passing over my radiator I think. I had a little Ford Fiesta before in which the fan wouldn't switch on, so I hardwired it directly to the battery and ran a switch through to me so I could turn it on when needed, and it wouldn't take long sitting in traffic or at a set of lights before I would see the temperature gauge begin to rise signalling me to flick the switch, especially in the summertime where we routinely experience days that are over 40 C (104 F) and get up to and even exceed 46 C (115 F) in the peak of summer.

    So to re-cap:

    * I've seen it spike and fall 3 times now, all within the first few minutes of 2 separate trips, not long after reaching operating temperature.
    * The needle moved as fast as it could.
    * Before spiking, it fell slightly below the normal position for a few seconds.
    * I also had one occasion where the needle was in the red. I'm not exactly sure how long it was there before I noticed, but it wouldn't have been long as I make it a habit to routinely check my instrumentation every 30 - 60 seconds depending on driving conditions.
    * After noticing, turning engine off for a minute while waiting for lights to change, then starting up again in an attempt to get off main road and park somewhere, the needle fell back down to below normal, jumped around for a bit in erratic movements, then settled at 12 o'clock.
    * There were no signs of actual overheating upon pulling over and inspecting.
    * My heater is blowing hot air through leg and windscreen vents, but not through the dash vents, not sure if that's normal?
    * When turning on heater, the temp drops a little, but before long settles back into the normal position. (I am assuming there is a relatively large range of temps that constitute "normal" so it displays at 12 o'clock and doesn't waver even though actual temps may be going up and down within the specified range? Is that correct?)
    * The car doesn't overheat sitting in traffic or travelling (very) slowly, pointing to a working fan.

    If I were to hazard a guess, and I am not qualified to do so, that's why I'm here seeking opinions of those far more knowledgeable, I would say that whatever sensor/s the temperature gauge is reading from are occasionally giving false signals, or, the instrument cluster itself is having issues, or there are pockets of air in my cooling system (least likely I think). But I could be SO far from the truth here.
    If the instrument cluster was having issues, would a hard reset help?

    Again, any suggestions on this are greatly appreciated.

    Cheers.

  5. #5
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    If you want to diagnose further, try looking at the coolant temperature in the OBC secret menu (http://www.bmw-driver.net/forum/showthread.php?t=31204) when the problem occurs and see what it says.

    If it really moves that quickly, it does sound more like an air bubble or sensor malfunction to me. If you see the temperature jump up to like 150C+ in the menu when it happens, I'd suspect the sensor.

    Regarding the heater: do you have climate control? There's a dial in the middle of the center air vent that you need to turn to the red side to get hot air out of the top air vents. If you don't have climate control, chances are that you will not get hot air out of those air vents (my old E36 without cc didn't blow hot air out of the top vents, never had an E46 without climate control so not entirely sure. It's a BMW 'feature' to keep the driver alert).

  6. #6
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    Actually.. Your story about the temperature spiking when the engine reaches operating temperature makes me more suspect the thermostat. It might be sticking 'closed' for a little bit before it opens.

  7. #7
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    You drive 240km to and from work? Buy a Honda. Yikes! /s

  8. #8
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    Raddee.

    Funny you should mention that, I actually did this on Friday afternoon on my way home from work (it occurred to me moments after posting my last "update"), and this is where I now suspect it is either an issue with the sensor or the instrument cluster itself as it is now spiking and remaining there for a few seconds at the start of every trip and when it spikes my OBC reads -128. Is this a default value for faulty readings?

  9. #9
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    Oh, and Marco, yes I drive 240kms a day to and from work. Why would I want to buy a Honda? YUCK! Besides, Honda's require Honda only parts to run well and they are nowhere near as cheap to own as a Toyota, Ford, or Hyundai down here in Australia, nor will they last as long. Honda's are actually quite expensive here. If anything I should buy a bike and cut my fuel bill down from $160 a week to $40 a week. (Fuel is quite expensive here, I only put in the premium 98 and at the moment it's around $1.70 a litre, I'm averaging around 8L/100km according to my OBC readings)

    Raddee, ahh, yes I do have that and wondered what it was for, thanks, I thought it weird that I wasn't getting hot from those vents but thought it might have been a "feature" as hot air blowing in your face can make you sleepy. lol.

    **edit**

    I posted a reply before this one but it had to be accepted by a moderator first, though this one didn't. Does that moderator filtering process end after making a certain amount of posts?
    Last edited by MilesWilliams; 06-04-2018 at 08:53 PM.

  10. #10
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    I concur with your opinion of Hondas. My wife has one. Yuck is the proper term. I suggested it as they tend to be more reliable than a bimmer.

  11. #11
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    MauiM3Mania is offline Observer/Master Skeptic Moderator
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    Quote Originally Posted by MilesWilliams View Post
    ... I posted a reply before this one but it had to be accepted by a moderator first, though this one didn't. Does that moderator filtering process end after making a certain amount of posts?
    Yessir. Thanks for your patience.
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