Coolant temp gauge fluctuating

[HRF1T2020]

Hi

Started yesterday noticed whilst driving my 18 plate fiesta mk8  Zetec 1.1l ti-vct 26k on the clock

the temp gauge didn’t hit the usual just below the centre line , carried on driving and the needle started going down nearly to the first line then would go back up and continued to do so for a 40min drive just moving little bits which isn’t right

the coolant level is fine, I’m getting hot air blowing in car ok, the rubber hoses all feel hot apart from bottom big hose from radiator is warm, car drives fine to drive 

I’m edging to thermostat stuck open but would like any other suggestions or anyone had the same 

 

got my other half to take some pics as it was happening and i did when stopped

dropping car off at my usual garage tomorrow and hope it’s a easy fix 

[HRF1T2020]

I’m taking that this is the thermostat housing? If so looks quite accessible near the top on this engine

is advisable to replace the whole housing or just the thermostat it’s self?

[TomsFocus]

There aren't many 1.1 owners on here to give personal advice.  It does look like the thermostat housing just simply unscrews at the right hand side (on pic) and should be easy to replace alone if that's any help.

Is the radiator fan on flat out for the air con btw?  Just seems an odd coincidence your engine is over cooling in extreme ambient heat!  

[HRF1T2020]

I’ll give it a try in a moment without the turbo there is more room in the engine bay and the mpg is great 

 

[HRF1T2020]

So just been out and A/C Fan does work straight away, was a struggle to get out as I’d got it set on max and recycle 32c outside was a hit after 5 mins 

 

[HRF1T2020]

Dropped car off there busy but hopefully can take a look today

They said sounds like the thermostat and came for a ride with me to see

Whilst idling got up to 90c then after a short while during the trip it started to head to the 75c and hover around in that zone never going above the 90c or dropping below the 75c

Picture is after a 40 min journey long dual carriageway and slight town traffic

 

Hopefully it's a easy fix and is the thermostat, only had one fail in the past on a MG ZS I had

[TomsFocus]

Last 'stat I had fail was on a 2006 Vectra...couldn't believe it when they charged me over £70 just for the part!! 😮 

[HRF1T2020]

15 minutes ago, TomsFocus said:

Last 'stat I had fail was on a 2006 Vectra...couldn't believe it when they charged me over £70 just for the part!! 😮 

Yeah I've only had one fail in the past guess been lucky

 

Mechanic who came out said they'd test it to make sure but they were certain that thermostat's these days come fail safe so stay open if any problems, also didn't rule out the sensor, but was swinging to thermostat being the problem, hopefully they can look at today and it resolves the problem, will keep updating.

I don't get if failed open why it goes above the 75c and not just sit cold

[HRF1T2020]

So just picked the car up and the garage replaced the housing and thermostat refilled the coolant and road tested it and the needle sits where it should just kissing the 90c

I took it for a little spin all good needle did not move

Garage said as a side to just check the coolant level in the morning in case needed a top up but were pretty sure would be fine

So looks like the Thermostat was the pesky blighter that was causing the issue if anyone else has this problem further down the line.

[TomsFocus]

That's got to be the one of the quickest fixes on here for a while!

[HRF1T2020]

4 hours ago, TomsFocus said:

That's got to be the one of the quickest fixes on here for a while!

It was quick I use same garage for many many years and got me in fast, wasn’t expecting it as they were v busy but like to get things fixed ASAP 

[charliec46]

I've just had the exact same symptoms on my mk 8 1.0 eco boost. Does anyone know if its likely to be the thermostat on the 1.0 engines (turbo on the front) and if so where the thermostat housing is located