if the base of the PSU doesn't seat fully against the bottom of the tank,you will get the efect of a low reading when full,and lots of extra reserve at the bottom as the pump base with the pivot will be displaced upward in the tank volume .there's two types of PSU that can be fitted to the 98 disco .although this is a common fault from 98 through to the 2000 model it can be resolved by fitting the new design /white plastic connector.try any disco forum and you will find this to be widely discussed.
mech monster, October 2011
