92 K1500 5.7L Cooling system temp fluctuations

[Rodeo Ron]

My brother has a '92 K1500 5.7L in which he had a leaking water pump. He replaced it with an Autozone unit. After replacing the pump, he now states he is experiencing fluctuating temperatures on the gauge. He has little heat at the heater, even after letting the truck idle and after driving it. This was not a problem prior to replacing the water pump. He has put approximately 200 miles on since the replacement and it has been about 2 weeks since he replaced it. He believes he has all the air out of the system, as he has checked the overflow container and radiator several times and the coolant level has not gone down. It sounds similar to a recent post, but without the additional issues. Because this now "suddenly" appears after the pump replacement, we are thinking it is not the temperature gauge sensor or bad thermostat. We are thinking possibly still air in the system or water pump cavitation. Anybody with similar symptoms? We are open to ideas. Thanks in advance for replying.

[aleekat]

Still sounds like air in the system. Park nose up, pull the cap and let it run, top off as necessary.

[Rodeo Ron]

Thanks, I'll have him give that a try.