C350 excessive pressure in coolant system

[mogaleworldwide]

Hi I have c350 M276 w204 v6 and having few issues with coolant circulation.car is not overheating and sits around 90d.coolant pipes are very very hard after short drive and alot of pressure in expansion tank. Top radiator hose very hard as if it wants to explode. New cap, new coolant reservoir, new radiator, new water pump, new thermostat. When you open cap after trip, it releases pressure but goes back to same thing after short drive.
Any info much appreciated

 

[Uncle Benz]

You need a litmus test of the cooling system to check for exhaust gasses in the coolant

 

[grahamcol]

As Uncle Benz above. Almost certainly head gasket/s issue.

 

[Uncle Benz]

Some of these cars do have an “on demand” water pump. Might be worth checking too