Intel i7-8700K Thermals & Delidding
We’ll start this one with thermals and delidding, since that’s been a popular topic lately. We’re running these tests with fixed frequencies and voltages, as that’s the only way to properly control for fluctuations in CPU behavior. We used Rockit Cool’s $40 delid kit to remove the IHS. It proved trivial to use and worked flawlessly which, for a $40 kit, is pretty damn good. We can recommend this one for Coffee Lake delids – the previous model for Kaby Lake CPUs will also work here, and delidding the 8700K is easier than the Skylake X CPUs as it lacks the dual-substrate layout.
Delidding the CPU was matched with removing the silicone adhesive from the IHS, and applying Thermal Grizzly Conductonaut liquid metal.
i7-8700K Delid Thermals: Blender at 4.9GHz / 1.4Vcore
Let’s start with the more exaggerated results: When testing Blender with a 4.9GHz frequency and 1.4 core voltage, our 8700K with Intel TIM and an NZXT X62 landed at 76C average core temperature, with a 10-second peak of 76.6C and a liquid temperature of 40.65C. The liquid metal version at the same frequency and voltage measured at 52.59C, or a reduction in average core temperature of nearly 24C.
Liquid temperature measured about the same as before, at 39.82C. Looking into this further, we realized that, measured at a current clamp on the EPS12V rails, the 8700K with TIM was drawing about 10-20W more power at the same voltage and frequency. We’re not yet positive, but our present theory is that this outcome is a result of power leakage reduction on the CPU as a result of improved energy transfer efficiency from the die to the IHS.
i7-8700K Delid Thermals: Prime95 4.7GHz / 1.35Vcore
Testing with Prime95 28.5 and the CPU locked to 4.7GHz core, 1.35Vcore, we found the delta much closer than in the earlier overvolted test. The TIM test plants us at 62.6C average core temperature, with the 10-second high at 63.82C. Liquid temperature is effectively matched to the liquid metal version, at 39.6C versus 39.8C. This is within our test resolution and error. Using Conductonaut, we’re at 52.59C, for a 10-degree reduction in average core temperature.
This isn’t as big of a deal as with the Skylake-X CPUs, where we were constrained in overclocking by thermal limits, but is still worth considering for higher voltage overclocks. Coffee Lake actually runs reasonably cool, all things considered, and doesn’t need a delid for consumer overclocks (like the 7960X did). That said, a 10-20-degree reduction is no small feat, and means lower fan RPMs to achieve the same temperature. For anyone planning to push higher overclocks, we can recommend the liquid metal and delidder that we used. If you’re worried about successful delids, we’ve heard that Silicon Lottery plans to start binning Coffee Lake CPUs within the next week, and they offer a delidding service on frequency-binned CPUs.
As for the results here, Coffee Lake clearly isn’t in nearly as much need as Skylake-X for delids with overclocks. To be clear, none of the CPUs “need” to be delidded – but Skylake-X benefits in big ways from the move, as we were becoming thermally constrained prior to encountering voltage constraints when overclocking. With Coffee Lake, the constraint was primarily voltage or frequency stability, not thermals. The improved transfer efficiency does help reduce power leakage and benefit everything a bit, of course, but it’s not a hard requirement for overclocking. There are big gains to be had from delidding the 8700K, they just aren’t as ensconced in grandeur as the Sky-X delidding. The CPU works just fine without a delid. We’d still recommend it for serious overclocks, but it’s not “needed,” as some earlier rumors falsely indicated.