Mazda 3 - Temp gauge fluctuation

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Sun 16 Nov 2014 12:19
Mazda 3 - Temp gauge fluctuation - balleballe

Wondering if anybody can help here, I've noticed this problem for a few days now but today was very apparant.

I started off on my 35 mile journey today, after 3 miles or so the temp gauge was half way, where it always is when it's fully warmed up.

Around 8 miles in the gauge temp dropped slightly, then after another 8 miles it went back up again, then back down a tad. Never had that before and cannot understand why. Is it something to do with my radiator or coolant? I'd rather sort this out before it causes problems.

It was very cold today it that makes any difference.

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Sun 16 Nov 2014 12:59
Mazda 3 - Temp gauge fluctuation - Manatee

Does it coincide with the cooling fan starting/stopping?

Edited by Manatee on 16/11/2014 at 13:02

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Sun 16 Nov 2014 14:03
Mazda 3 - Temp gauge fluctuation - brighteyes
If it's got an electronic thermostat it could be the temperature sensor. If the movement is only minimal I wouldn't worry about it, just keep your eye on it. All this is on the assumption that you're not loosing any water.
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Sun 16 Nov 2014 17:53
Mazda 3 - Temp gauge fluctuation - balleballe

It doesn't seem to coincide with the fan it's quite odd as its never happened before.

On my return journey I was doing 65mph. For the first 5 miles the gauge was midway (where it's supposed to be). It then dropped 2 notches for 4 miles, then back up a notch for a couple of miles etc.....

Water level seems fine, as does the coolant level.

I hope replacing the temp sensor isn't a massively expensive job as it looks like that's my first protocol here

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Sun 16 Nov 2014 18:47
Mazda 3 - Temp gauge fluctuation - elekie&a/c doctor

Replacing the temp sensor could be a waste of time.There is only one on these and it is part of the engine control system.If it were faulty,you may get engine running problems also.

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Sun 16 Nov 2014 19:02
Mazda 3 - Temp gauge fluctuation - balleballe

Could there somehow be air in the system? This is what a friend of mine reckons, although he's a car enthusiast and not a mechanic.

The coolant was topped up a year ago but hasn't been fully changed for at least 3 years(my length of ownership). is it worth a try draining and replacing the coolant?

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Mon 17 Nov 2014 12:09
Mazda 3 - Temp gauge fluctuation - dieselnut

If it has a standard wax capsule thermostat it may be sticking open.

They are usually cheap to replace.

Some coolant will be lost when changing this, so coolant can be changed at the same time. Make sure you bleed all the air out including the heater.

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Mon 17 Nov 2014 12:16
Mazda 3 - Temp gauge fluctuation - balleballe

Not sure what type of thermostat it is, but it's only £7 on eurocarparts so possible worth a shot regardless

Going to buy a radiator flush also, as heard it's a good idea seeing as the car/radiator is 10 years old!

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Mon 17 Nov 2014 12:24
Mazda 3 - Temp gauge fluctuation - skidpan

You don't say what engine you have but our old C-Max with the 1.6 TDCI engine had a temp gauge that went up and down like a brides night dress from the day we bought it to the day we sold it 5 years later. Dealer changed the stat under warranty but it made no difference. He thought it might need an ECU update but none was available.

Car never used any water and never had a cooling problem. Just learned to ignore it eventually.

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Mon 17 Nov 2014 12:50
Mazda 3 - Temp gauge fluctuation - balleballe

Sorry - i've got the 2 litre petrol

It wouldn't bother me if it had always done this - but i've had it for 38k miles now and it's always stayed midway on the gauge once warmed, never any higher or lower.

That's how I know something is wrong

Edited by balleballe on 17/11/2014 at 12:51

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Sun 30 Nov 2014 11:29
Mazda 3 - Temp gauge fluctuation - balleballe

Just an update. Took my car to the garage.

They noticed my exhaust was broken, split in the middle apparantly...that's been welded together, and a sticking thermostat was cited as the most likely reason.

Thermostats been replaced and the problems gone. A nice cheap fix.

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