Have now used Silver Arctic V compound. It's very good. Idle temp is now 40C. Thanks for all your help.

No - the problem is still the same. Case airflow = 2 fans front blowing in (medium speed), 2 fans rear blowing out(high speed), 2 fans/airplex 160 blowing in(medium speed) Room temperature =23C External temperature of pump feed connector=36C How do I measure water temperature and water flow? I can see the water flow through the Aquatube glass and it looks good. Does anyone else have an intel 580 cpu. What temperature do you have?

Thanks for the replies. Sorry, I was not clear - No air in system = no air in airplex or cuplex evo. Looking through plexiglass water level is 16mm from the top. The glass feels quite warm. As regards to motherboard sensors I don't think that is a problem. The sensor will have the same inaccuracy no matter which cooling system is used. I'll try reseating the block. Vielen Dank.

System - Lian Li PC70, Asus P5AD2-E premium, intel 580 I decided on the Aqua system because my PC is very noisy. The CPU temperature is 44C when idle and 70C when working hard. I have now installed the Aquastream 12V, Airplex 160, Cuplex Evo 1.1 and blue Aquatube. 4 Papst fans in rear. OK, it's quieter. CPU temp on idle is now 50C, when busy over 75C and rising slowly. Can not see any air in the system and water flow is good. What else can I check?