Re: 02 ranger 2.3
If , as suggested , the thermostat is jammed open you will get little or no heat , especially in winter . You could check the heat in the hoses to the heater core / matrix which will give a further indication of whether thermostat is knackered or not . Also try bleeding the system . I have had some temp senders that failed to operate due to not earthing because of rust round threads in block / cyl. head or using tape on threads . Others failed due to not getting coolant to sensor due to build up of rust and sludge . Cleaning out and getting flow of coolant cured the fault . Other possible causes but would check out the suggestions in the replies given first before getting in too deep .
Never, never, never give up.