Temp gauge raising

Since a few days my temp gauge goes up until it nearly reaches the red section. Then it drops in few secs to its normal temp.
I noticed when this temp raises (slowly to the red) and kickdown the pedal the temp drops again. After it dropped to its normal temp it doesn't raise above its normal temp.
It is only for the first 10 miles (cold engine) and not when starting the car again after driven 30min.

it seems to me when the engine is idling the temp is pretty high... I don't know the scale, but guess it is 100 celcius.

Any ideas, I was thinking of the thermostat, that opens to late.

It sounds like some air trapped in the system. Possibly due to head gasket or intake leak.

if you are getting exhust into the cooling system it will have pressure under the rad cap when cold. With the rad topped up ,leave the rad cap off , start the engine and rev it up , if its shooting antifreeze in the air then you more then likely have a bad head gasket, very commen on these vans

You should say so, but there is no sludge in the oil cap or engine, and the coolant is very clean. Also the gaskets really look like new.
Funny thing is that it is only after a "cold drive" for about 10 miles. The gauge gets almost to the red bar and suddenly drops to about 80-85 degrees celcius. Then it stays there. When I hit a traffic jam, it get a bit hotter, but nothing near the red bar. It reaches just around 100.

I can't remember to see a fan run. Does it run constantly ?

Anyway when I leave my car on the driveway for an hour and I drive again the gauge stays at say 80-90 degrees.

When the gauge almost hits the red bar, I kickdown the gaspedal and it drops in a few sec.

When it was a gasket issue, I would say it should have this all the time. And I'm not loosing coolant in any way. Last time I filled it up (g12 coolant) was about 6 months ago. And the coolant is still at normal level.

The fan doesn't run constant. It also has 2 speeds.