MGF VVC, engine temp problem

On fierce acceleration, up through the gears, 2nd to 4th, at 6k rpm, temp gauge drops like stone to Cold, almost immediately. But cruising quietly at up to 3k temp normal, and at prolonged idle in traffic.

Should I be worried, please?
Or can it wait for investigating service in March.
Many thanks, Miles

Sounds like you might have a loose electrical connection, under hard acceleration the engine can move more on it’s flexible mountings this can pull on the wiring, and if a terminal is loose, well that could explain why your gauge suddenly heads south.
Check you terminals.
Mind you I think you should also check your engine mounts in case the movement is caused by a failed or failing mount

Mine did exactly the same although it's not a VVC, I replaced the gauge sender but it made no difference, eventually I traced it to the thermostat, I guess it was opening up suddenly on heavy acceleration and flooding the sensor with cold water. I took the opportunity to do a PRT conversation at the same time.

It could be associated with the sensor on the engine, I had something similar early on in ownership of the f. I bought a new sensor & once in to the engine compartment I found there has been a weep around the sensor which created a carbuncle of calcite (it wouldn’t be calcite but it sounds better than white stuff).
My lad was in charge as I’d been unwell & he cleaned it up, ensured there was earthing integrity & the problem disappeared, then with the replacement going in the spares box, the original is still in & keeping me up to date with the engine temperature.
M

Thanks your quick reply.
The needle doesn't drop as if signal lost.
It drops steadily until reaches C as the revs increase under full throttle over 15 secs or so, and climbs back to normal similarly as soon as I back off.
Which led me to believe thermostat might be problem?
It had new water pump fitted 6 months ago, but not sure about thermostat.
Regards Miles

You may well be correct in your assumption, however if you are intending to change the thermostat do consider replacing it with the PRT system off the later tf. I suspect you will find several f owners have done this & although a moot point as to how much better than the block mounter original, it is a dickens of a lot easier to change when/if that gives notice at a later date.
I did mine several years ago & although I feel it takes longer to reach optimum temperature it is considered a friend to the head gasket. Note I use the word considered, it doesn’t give you free reign to ignore the header tank. Consider changing that also if it looks old & dirty, the seal where top & bottom are moulded together fails when too many summers are past.
Do you have a low coolant alarm? Do fit one if not.
M

Thanks again.

I have spent a lot on my pride'n joy and am reluctant to incur more until next service, due in March.

Shall I be running much of risk by delaying investigation and repairs you suggest till then??

One thing occurs to me if you want to keep an eye on your temperature but are reluctant to delve too deep until your next Big One & that is to fit a digital thermometer.
There is one that I’ve used in a couple of test beds & it’s sensor screws directly into the rear bleed screw hole. As I recall the terminals are screw & although you might have to extend the cable into the cabin it requires nothing other than 12v.
If you want more info I’ll have a rummage & find a reference. They’re not Ninas accurate but they are within points of my standard & they’re not expensive.
M

I think I will take the risk and leave well alone until the March service. I shall only be using the car locally until then.

But thank you all for your comments, which provides me with a list of improvements to get done then.
All the best, have a good Christmas.
Miles

Have you noticed any drop in coolant level over time ?

Thankfully, no! Level is about 1mm below protruding tab in reservoir - but hard to see from above - consistent pale salmon pink colour and with no sign of any globules, etc. Hasn't been looked at since last service in mid March.
Thanks for your interest, and regards, Miles