  We present upper limits on the X-ray emission for three neutron stars. For
PSR J1840$-$1419, with a characteristic age of 16.5 Myr, we calculate a
blackbody temperature upper limit (at 99% confidence) of
$kT_{\mathrm{bb}}^{\infty}<24^{+17}_{-10}$ eV, making this one of the coolest
neutron stars known. PSRs J1814$-$1744 and J1847$-$0130 are both high magnetic
field pulsars, with inferred surface dipole magnetic field strengths of
$5.5\times10^{13}$ and $9.4\times10^{13}$ G, respectively. Our temperature
upper limits for these stars are $kT_{\mathrm{bb}}^{\infty}<123^{+20}_{-33}$ eV
and $kT_{\mathrm{bb}}^{\infty}<115^{+16}_{-33}$ eV, showing that these high
magnetic field pulsars are not significantly hotter than those with lower
magnetic fields. Finally, we put these limits into context by summarizing all
temperature measurements and limits for rotation-driven neutron stars.
