Engine temperature (Gauge) fluctuating ... normal ??

SmiTTy on 23/06/2015 - 15:52

Hi All

I've got a mazda3 (about 2005-6 model) which I recently put in for a oil change etc.
When it came back .. i noticed the temperature gauge on the dash sometimes fluctuates from quarter to half way as I drive (this might happen 5-6 times on a 1 hour journey). I didnt really notice it before, so Im not sure if this is normal - but certainly on my other cars I know the needle stays constant throughout the whole journey. its on the lower end which is why im not so concerned at the moment (i.e not overheating)

Is this an issue? Do I need to get this looked at / fixed ?

Thanks

Automotive

Comments

  • highon2str on 23/06/2015 - 15:58

    For a start, when the engine is cool, check your coolant level (carefully - risk of burns!) and make sure it is topped up at the right level.

    • [Deactivated] on 23/06/2015 - 16:16
      +1

      Also make sure that the cooling system is free of air by bleeding it.

      • onlyletters on 24/06/2015 - 14:21

        Most systems bleed themselves, but he didn't have a coolant change, it was only a oil change.

  • nocure on 23/06/2015 - 16:23
    +2

    Could be a faulty thermostat ..mine will sit and stay on half in summer but in winter it fluctuates between quarter and half…PS.lot cheaper to do the oil change yourself.

    • SmiTTy on 23/06/2015 - 16:28

      Thanks .. is there any way to check this? (or is it somehow just trial and error)

      • nocure on 23/06/2015 - 16:37
        +1

        It needs to be removed to properly test it…as long as the needle dosen't go over halfway it should be fine..just keep your eye on it particularly on a long trip.

      • [Deactivated] on 23/06/2015 - 18:18

        If it seizes closed you'll blow your top radiator hose.

  • highon2str on 23/06/2015 - 16:58

    Good luck, hope the experts here fix your problem.

  • John on 23/06/2015 - 17:55

    If your engine is genuinely over heating, you can feel it in your air conditioning as it will blow a warm air. I've had this before and found out the coolant was leaking out from the radiator hose.

  • nocure on 23/06/2015 - 18:53

    your air conditioning as it will blow a warm air.

    How does air con blow warm air..?

    • John on 24/06/2015 - 12:42
      +1

      By blowing a warm air?

  • TopGun31 on 23/06/2015 - 20:57
    +4

    When you cold start your car the thermostat is closed, blocking coolant flow throughout the engine. This is to help the engine warm up to running temperature.

    As the temperature of the engine and hence thermostat increases, the thermostat opens (usually about 90 degrees or so) and lets coolant flow throughout the engine and through the radiator, this cools the engine. You can see the cycle will continue, the thermostat will close when it gets to cold and open when it gets to hot. Effectively holding the coolant temperature at that of the thermostat (90 degrees or so).

    However some times, the car can't reach the temperature to open the thermostat, this isn't necessarily a bad thing. A typical example is a cold day driving on an open road, the engine will naturally stay very cool from the airflow. In this case your temperature needle will sit below half and probably fluctuate as you slow/speed up approach traffic etc.

    In busy bumper to bumper traffic with little airflow, assuming its not freezing cold, the temperature gauge will most likely reach halfway (or wherever the thermostat opens) and stay there as the thermostat opens and closes to keep it at the running temp.

    If its fluctuating wildly unlike described above, it could be air in the cooling system or a faulty thermostat perhaps.

    tldr; sounds normal, assuming it doesn't overheat in traffic its probably fine.

  • SmiTTy on 24/06/2015 - 00:04
    +2

    thanks everyone for your comments !!

  • Marble250 on 24/06/2015 - 09:15

    Sounds like the water temperature sender is on the way out!

  • Kkuba on 24/06/2015 - 16:59
    +2

    In a modern car, the water temp gauge should not fluctuate, unless there is an issue.

    As others say, coolant temperature may fluctuate a bit, as you drive, then sit in traffic, however, a modern water temp gauge is calibrated that the middle of the gauge (where the needle normally sits once at operating temperature), is not a specific temperature, but more like a temperature range, for example 70-85 degrees, or whatever the normal operating temps are for any specific vehicle. This means the needle should point to the one position if the water temperature does not go outside of those limits. This accounts for the coolant temp fluctuations that occur normally, and makes the gauge a bit more 'user friendly', so if it starts to move, you know it is going out of the optimum temperature range.

    Secondly, a car that is running too cold is not good for the engine. If the engine cools a bit too much, the EFI system may think that the car is still in the warmup phase, and add extra fuel. This extra fuel can dissolve the thin lining of engine oil on your cylinder bores, causing potential engine damage (glazed bores). Don't worry too much, but I wouldn't leave this for weeks.

    Certainly sounds like your thermostat is not closing. This means you are getting more cooling than required, and the engine is running cold. See if you can correlate the temperature drop to when you are moving, and the rise to when you are sitting at the lights/in traffic.

    Hope that helps a bit.

    • SmiTTy on 24/06/2015 - 17:07

      Thank you muchly .. that is definitely helpful !

    • Marble250 on 24/06/2015 - 23:00

      All that's great and sounds like it's straight out of the ops manual, except the OP hasn't said his car is overheating!….if its only a fluctuating needle on the gauge and the water temp isn't rising…..you can bet your left one it's the sender!

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