Temp Gauge Going In To Red - Not Overheating

My MGF started playing silly buggers today, it has been hot here (28c) and on a trip earlier the temperature gauge suddenly went beyond red, I pulled in quick and noted the car didn’t seem to be exhibiting any signs of overheating, engine didn’t seem or smell overly hot, no radiator fan running, only the engine bay fan for a minute or so. 

With some cycling of the ignition the gauge dropped pretty quickly within about 10 minutes and when it showed below halfway I checked the coolant, no undue pressure, fluid bright green and at the usual mark, oil on the dipstick was like new, no evidence of moisture. 

I then carried on the remainder of the 20 minute drive home and the gauge stayed just under halfway as normal. Only when I was parking did the gauge start to climb again. 

The radiator and condenser fan fuses are fine, could it be a faulty sender, or maybe fan relay or something? It certainly doesn’t give any indication that it’s a potential HGF. 

I should also add, the car has been absolutely fine previously and no recent coolant work to cause an airlock etc. 

1st thing is 28C isn't hot.......it's just a nice day! 🤣
Before we do anything rash that will have you spending all your fun tickets.....lets start with the things that are free or likely to cost very little.

Have you bleed the cooling system? If not I suggest you do at all 3 points.

Once you're satisfied that isn't the culprit, Is the coolant cap playing funny buggers? Perhaps you should check the thermostat is doing it's job properly too.

Is the radiator got a lot of crap blocking the airflow? When I inherited my Dad's old Ford Fairlane, I found it ran hot all the time......upon investigation I found the radiator had a nice wooly blanket of dog fur between it and the air conditioning condenser, the dog beds in the garage were right in front of where the car was parked, every time he'd start the car the loose fur got sucked in to the air intake under the bumper by the engine driven fan!
Now that was an extreme case, and as our cars have a thermostatically controlled fan is unlikely to be your exact problem but the radiator's air flow could still be blocked.

Once you've gone through that lot report back with your findings and we will go from there!

Haha, you’re right it was 42c a few days ago. I’ll start going through your recommendations and check. I also have a low coolant alarm which I might even have time to fit in the next couple of weeks. First time in my first year of ownership it’s played up!

Stop buggerising about and fit that low coolant alarm as a matter of priority!
Consider yourself told! 🤣

Consider it at the top of the list!

You've had that coolant alarm for 6 months! Don't put it off until it's too late,

If anyone else wants one, I have a few in stock that I can send out in the New Year

That's two of us telling you to get off your arse and fit it,,,,,,,,,,,,,,more will join in the chorus the longer you leave it, so just do it NOW!

Go on. You know it makes sense

We will not let it drop , unless you fit it !!!😆       NEXT ! 🙃😆

It could be the most productive hour you spend on your car this year. I’d be doing it in a day or two, certainly no later. Use tomorrow to plan the job & make a start first thing the day after & no distractions until it’s done.
M

And you thought a missus could nag!

From experience,  sudden changes in the temp gauge can be related to air bubbles sticking around the temp sensor.