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(Abridged) High-mass star formation is far less understood than low-mass starformation. It entails molecular outflows, which disturb the protostellar clump.Studying these outflows and the shocked gas they cause is key for a betterunderstanding of this process. This study aims to characterise the behaviour ofmolecular outflows in the most massive protostellar sources in the SouthernGalaxy by looking for evolutionary trends and associating shocked gas withoutflow activity. We present APEX SEPIA180 observations (beamwidth $\sim$36")of SiO outflow candidates of a sample of 32 luminous and dense clumps,candidates to harbouring Hot Molecular Cores. We study the SiO(4-3) lineemission, an unambiguous tracer of shocked gas and recent outflow activity, theHCO$^+$(2-1) and H$^{13}$CO$^+$(2-1) lines. 78% of our sample present SiOemission. Nine of these also have wings in the HCO$^+$ line, indicating outflowactivity. The SiO emission of these 9 sources is more intense and wider thanthe rest, suggesting that the outflows in this group are faster and moreenergetic. Three positive correlations between the outflow properties werefound, which suggest that more energetic outflows bear to mobilise morematerial. No correlation was found between the evolutionary stage indicator$L/M$ and SiO outflow properties, supporting that outflows happen throughoutthe whole high-mass star formation process. We conclude that sources with bothSiO emission and HCO$^+$ wings and sources with only SiO emission are invirtually the same advanced stage of evolution in the high-mass star formationprocess. The former present more massive and more powerful SiO outflows thanthe latter. Thus, looking for more outflow signatures such as HCO$^+$ wingscould help identify more massive and active massive star-forming regions insamples of similarly evolved sources, as well as sources with older outflowactivity.

SiO Outflows in the Most Luminous and Massive Protostellar Sources of the Southern Sky