Thermostat/Temperature Gauge Fluctuating - Mazda3 Forums : The #1 Mazda 3 Forum
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post #1 of 13 (permalink) Old 01-25-2020, 02:32 PM Thread Starter
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Exclamation Thermostat/Temperature Gauge Fluctuating

(This was also posted in the electronics as I'm not too sure whether it's engine related or the electronics.)

I've had my car off the road for a couple of months and I've just got it running and going again, however, the temperature gauge is fluctuating a lot so sometimes it'll be at the normal running temps (which it should be at) and then drop all of a sudden to cold or near it. Any help would be really good. Thanks!

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Last edited by dougalmcg; 01-31-2020 at 11:16 AM.
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post #2 of 13 (permalink) Old 01-25-2020, 08:45 PM
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You need to post whatever diagnostics/checking you've done so far, in order to avoid wasting everyone's time.

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post #3 of 13 (permalink) Old 01-25-2020, 08:54 PM Thread Starter
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Well, I haven't been able to do much testing, as I stated, I only just found this issue and wasn't able to find a solution from anywhere else.

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post #4 of 13 (permalink) Old 01-25-2020, 09:39 PM
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You didn't state anything about testing. But if you haven't done anything, then start by checking the coolant level.

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post #5 of 13 (permalink) Old 01-25-2020, 09:48 PM Thread Starter
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Well, I did say that I have only just got it going so I haven't had a chance to do any checks. Either way, I will start testing tomorrow. The front radiator was changed recently and the system was filled back up and the levels so far have been where they should.

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post #6 of 13 (permalink) Old 01-28-2020, 06:29 PM Thread Starter
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After some small tests. I've figured out that the coolant levels are good. However, I have also noticed that when the car is stationary, the temperature gauge will go up to normal running temps, but if I then go for a drive, it falls all the way back down to cold again.

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post #7 of 13 (permalink) Old 01-28-2020, 09:00 PM
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When the gauge drops down, have you stopped the vehicle and checked the temp of the upper and lower radiator hoses? (i.e. cold, warm, hot) Also (again when the gauge drops down) how does the heat feel when you turn it all the way up?

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post #8 of 13 (permalink) Old 01-29-2020, 01:23 PM Thread Starter
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So recently, my car has yet another issue (possibly a dodgy starter motor), and I can't test it at the moment, however, yes when I was driving the car, the heater fans were consistent and stayed hot like usual and didn't change when the thermostat did. I plugged in an obd reader and saw the live coolant temp readings, it was getting around 70.c when warm, but then as soon as I moved off going not much faster than 30mph it came back down to cold again which dropped down to around 55-60.c in a matter of seconds.

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post #9 of 13 (permalink) Old 01-29-2020, 07:51 PM
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Sounds like your thermostat may be stuck open?
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post #10 of 13 (permalink) Old 01-29-2020, 07:53 PM
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Someone should fix the title of this thread. It's a thermostat.

Based on your latest post, I'm wondering if the thermostat has failed and is locked open. This would allow coolant to freely flow and prevent it from absorbing heat.

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