  The most nearby clusters are the best places to study physical and enrichment
effects in the faint cluster outskirts. A3158 located at z=0.059 is quite
extended with a characteristic radius r$_{200}$=23.95 arcmin. In 2019, A3158
was observed as a calibration target in a pointed observation with the eROSITA
telescope onboard the SRG mission.
  We determined 1d temperature, abundance and normalisation profiles from
eROSITA and XMM-Newton and Chandra data as well as 2d maps of temperature
distribution from eROSITA data. The velocity dispersion was determined and the
cluster mass was calculated.
  The overall temperature was measured to be 4.725$\pm$ 0.035 keV. The profiles
of eROSITA all agree on a ~10% level with those determined with XMM-Newton and
Chandra data. From the temperature map we see that the cluster lacks a cool
core, as noted before. The presence of a previously detected off-centre cool
clump West of the central cluster region is observed. Furthermore there is a
bow shaped edge near the location of the cool gas clump West of the cluster
centre. An extension of gas is detected for the first time further out in the
West. The velocity dispersion of the cluster was measured to be 1058$\pm$41 km
s$^{-1}$. The total mass was determined as $M_{200}$=1.38$\pm$ 0.25x10$^{15}$
$M_{\odot}$. The mass estimate from the M-T relation is significantly lower at
M$_{200}$=5.09$\pm$ 0.59x10$^{14}M_{\odot}$. An extended X-ray source located
South of the cluster also coincides with a galaxy overdensity with redshifts in
the range 0.05<z<0.07. These are indications that the cluster may be undergoing
merger activity. Another extended source located North of the cluster is
detected in X-rays and coincides with an overdensity of galaxies with redshifts
in the range of 0.070<z<0.077. This is likely a background cluster not related
to A3158. Additionally a known SPT cluster at z=0.53 was detected.
