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