Truck keeps heating up.
Well its a 93 4.0 This weekend I just changed out the t-stat and did a radiator flush now the dang thing keeps heating up on me. With the old t-stat it over heated for a split second to about 3/4 of the way, with this new one I can drive it on the freeway with no problems but then when it comes to city driving it often want's to go above half if I don't keep it up to about 1,000 rpms. Tonight when I filled up at the gas station I fired it back up and the heat went right up to 3/4 way again but then quickly settled back down to under normal operating temp. What would be causing this? maybe the water pump isn't doing it's job like it's supposed to be? Any insight would be delightful.