[2000izusu]

try grounding the heater core if nothing else works. that is from a ford tsb. as we all know ford had major heater core problems on the early 90's. also try to get a copper heater core. also stick the positve end of a digital volt meter in the antifreeze (via radiator cap) and the negative on the neg side of the battery. if you read anything over .5volts dc you got a problem and you need a major coolant flush. mike

p.s. if the truck is a real beater you can go the getto route and bypass the core and then go get a 12 volt heater that plugs into a 12 volt outlet. every auto parts store sells them.