Datacenters provide high performance and flexibility for users and cost efficiency for operators. Hyperscale datacenters are harnessing massively scalable computer resources for large-scale data analysis. However, cloud/datacenter infrastructure does not scale as fast as the input data volume and computational requirements of big data and analytics technologies. Thus, more applications need to share CPU at the node level that could have large impact on performance and operational cost. To address this challenge, in this paper we show that, concurrently fine-tune parameters at the application, microarchitecture, and system levels are creating opportunities to co-locate applications at the node level and improve energy-efficiency of the server while maintaining performance. Co-locating and self-tuning of unknown applications are challenging problems, especially when co-locating multiple big data applications concurrently with many tuning knobs, potentially requiring exhaustive brute-force search to find the right settings. This research challenge upsurges an imminent need to develop a technique that co-locates applications at a node level and predict the optimal system, architecture and application level configure parameters to achieve the maximum energy efficiency. It promotes the scale-down of computational nodes by presenting the Energy-Efficient Co-Locating and Self-Tuning (ECoST) technique for data intensive applications. ECoST proof of concept was successfully tested on MapReduce platform. ECoST can also be deployed on other data-intensive frameworks where there are several parameters for power and performance tuning optimizations. ECoST collects run-time hardware performance counter data and implements various machine learning models from as simple as a lookup table or decision tree based to as complex as neural network based to predict the energy-efficiency of co-located applications. Experimental data show energy efficiency is achieved within 4% of the upper bound results when co-locating multiple applications at a node level. ECoST is also scalable, being within 8% of upper bound on an 8-node server.