How to tell if heat sink is installed optimally?

[homebuilt]

I just installed a corsair hydro h50 water cooling heat sink on a i7-4790K.

It makes the CPU much cooler than the stock intel heat sink, but the temp still reaches more than 85 degree C when I run prime95 at 4200Mhz (I started low and gradually increase the multiplier until 85 degree). My mobo defaults to 4300Mhz, so I'm actually underclocking the CPU.

I wonder if maybe I didn't put the thermal paste on correctly. The idle temperature is about 33. Ambient is 25.

Is there a guideline on what temperature I should expect to see given the heat sink and clock speed, load, etc?

 

[Dark Lord of Tech]

That's about right for a budget cooler like the H50.

It's not a cooler to overclock with.

 

[getochkn]

Could simply be your fan curve for the rad fan's isn't high enough to move the heat from the rad's.

Also, I've found when using an all-in-one water cooler, it helps to have a rear fan blowing around air or one even in the drive bay blowing towards the MB. When you have a big hunk of copper and fan in the middle of the motherboard, it absorbs a bit of the ambient heat from the chipset and helps get it away from the MB. When you go water cooling, the CPU stays cool as hell, but other components start to suffer as their stagnent air flow around the mosfets, voltage areas, etc.

 

[Dark Lord of Tech]

A 212 EVO will even outperform a H50 by a couple of degrees.

 

[homebuilt]

A 212 EVO will even outperform a H50 by a couple of degrees.

Unfortunately, the 212 is too tall. I would have to remove the side case fan which I don't want to do.

Next time I build a PC I would get a fatter case so I have this option.