my coolant gauge reach operating temp and stay there in any outside teperature condition and any driving condition ( idle , traffic , low speed , high speed , highway cruising , spirited drive mid-high rpm ) but when i push very hard at WOT to redline with outside cold weather , temperature gauge drops suddenly and then return in normal operating temp in about 30 sec when rpm slow down.
Here's a video take a look to the temperature gauge , what could happen ? i don think this is normal , what do you think ?
https://www.youtube.com/watch?v=X7Ro69Rx9mE&feature=youtu.be

 

I think you're OK but maybe I'm wrong. How cold outside are we talking? Also, where are you going 310KPH at?

 

Oh, I see 4.5C or 40F. I think you're OK. Careful man, most of these performance tires aren't made to run that cold.

 

Temps dropping while moving and returning idling could be thermostat failing.

 

OP I have the same issue. I have swapped out for a new fuel pressure sender but it's still the same.

Btw noticed ur car revs to 7200rpm? Did u tune it to increase redline?

 

It is probably the stat then. Does your car take a long time to warm up?

 

Thanks at all for your replys , the dealer also thought it could be a failing thermostat , the only thing it sounds strange to me is that the temperature drop ONLY in this hard WOT pulls to redline with cold ambient temperature ( 40 F ) .
In all other driving condition the needle remain in perfect operating temperature so , is not like s65e90 said that temperature dropping while moving and remaine at idle , my temperature warm up in short time and remain costant while moving , also at high speed if the rpm remaine below 6000 rpm , so for example if i cruise in winter at a speed of 250 km/h in 6th gear partial throotle at 5000 rpm , coolant temperature remain constant , no matter how cold is outside.
So it seems the thermostat do its job fine in all conditions but at WOT it seems the high speed of water pump / high pressure in coolant overcome the t-stat ability to handle the temperature or it not responds faster enough to keep the temperature stable under high loads .
After temperature dropping in this Wot condition , it return in normal position in about 30 seconds while the car still moving at high speed but rpm slow down from 7000 to 5000 - 6000 , so it seems rpms / water pump speed create the " issue " .
Next week i'll try to replace t-stat like dealer saids and we will see if it fix.
Yes my car is tuned by rs-tuning , ecu and hybrids 16 / 24 s and rev limiter is raise to 7400 .
Those high speed runs were from German Autobahn
Here's another :

Accordly to speedo and rpms , indicated speed should be 350 / 352 km/ h , gps 330 - 332
My tires are Michelin Ps2 .

 

it'll happen on WOT pulls until the rads are up to temp, normal

 

Thanks 993 GT , nice info so in your opinion nothing to concern about ?
No risk for thermal shock haeds / block / head gasket when suddenly cold coolant enter in engine in those wot pulls ?
So if you were me to replace thermostat is worth ?

 

My car is doing same thing, car was checked and everything is ok.
Happens only during WOT on highway... I think that it is normal.

 

Yes maybe nothing to concern , my only doubt is because this is tje first car working this way . In all my other cars it not happens .
Yes this is my first car with rear engine / front radiators , maybe when car is warmed up in normal driving , and thermostat stay closed most of the time to keep operating themperature 80 - 85 C , coolant from the engine block is at 80 - 90 C and coolant in front radiators is maybe at 35 -40 C , so when suddenly push this cars at WOT , the coolant in engine also raise suddenly from 80 to 100 so the t-stat suddenly open and the high engine / water pump rpms push a lot of pressure moving the cold coolant from radiators to the engine dropping the temperature of coolant in the engine from 80 - 85 to 60- 65 C ???
The only thing i'm a little concern about is that this suddenly temperature change can put a thermal stress on the engine and head gasket ? I dont know ....

 

I would go ahead and change change the stat. It is a 30 dollar part plus the o ring and maybe 30 minutes of work.

 

Good to know , i was concerned for the labor cost to replace the t-stat , if its a cheaper job i think i'll do it , my t-stat has 56k miles , so if it doesn't fix , sure a bran new t-stat could reduce this temperature drop phenomenon .
Is necessary flushing all the coolant to replace t-stat ?

 

No. You will lose some though.

 

from my experience they all do it... 30L of coolant needing warmed up....it's not ideal but it happens, try to get the whole system up to temp before doing a big pull, even a small/light pull when the engine is up to temp to help warm the front end of cooling system warm a bit to reduce the variation
Never hurts to do P.M. on the car, worth a shot to see if it helps the situation a bit and have peace of mind