Mk6 Temp Gauge like rev count !!

[servicebarge]

Howdo

I have a 2.4 90bhp 350 RWD.

I have just fitted a new thermostat and now have a tempreture gauge that almost works like a rev counter when at high revs in 4th. (Slightly in 3rd as well but longer to react).

I can drive down the road at steady revs and the needle sits ok in the middle. Build the revs up high up to about 60-65mph and then the temp goes to the red in approx 10 seconds.
If i lift off and slow down it drops down again to normal within approx about 10 seconds.

I've tried stopping quickly and jumping out to feel the hoses but the temp is already dropping to normal by the time I've stopped - all hoses feel warm - by no means boiling.
The system does seem to have a bit of pressure in it.

Wondering if the temp sender is picking up a spurious signal? If so - has anyone changed one - thinking it's in the back of the head?

2 litres of red (comma) anti fr4eeze used in system.
New waterpump fitted when engine changed.

History
1.Original engine blew up last year and repalced with second hand engine 61k.
2. After about 200 miles of towing trailer/rallycar it spuriously shot up to the red. Stopped - left to cool and was then ok towing at various other times for about 400 miles.
3. Found that the oil cooler had started leaking oil into water system. Changed this for anonther one.
4. After approx 150miles towing rally car it spuriously overheated again (or at least the gauge went to red). Stopped - waited a while and was ok towing home for the next 100 miles.
5. Used daily (non towing) with no probs.
Present
Fitted new thermostat - the one that was fitted was one I had cut the middle out off after the spurious overheat.

Any advice folks?

Cheers

[APH]

My first thought was oil cooler, but see you had done that (although that dosent mean its still not faulty), possibly water pump failing, or could just be faulty CHT sensor. The temp sensor is a right pain to get too as, yes, its on the back of the block when looking under the bonnet (think intake manifold has to come off to get to wiring too, cant quite remeber as its been a wile since iv'e been round there!)

Just my two peneth on the subject, Best of luck,
Andy

[ake]

Is your heater working properly? cos it could be air causin your problems

[servicebarge]

AKE

It's not brilliant - strange but it doesn't get much hotter (or cold) when the temp goes up.
I've had the top heater hose off to make sure water coming out - was ok - but I don't know how high above the header tank the hater matrix is?

I've just remembered I've got a hand held infra red temp sensor that I will try on the block at the back of the head to see how hot it is getting when it does go into the red. Problem is the dash thing cools down so quickly!

Cheers