I have a 2000 Ford Ranger and the engine temp fluctuates greatly.
The temp stays close to normal until I turn the heat on,as soon as heat is turned on the engine temp drops to almost cold start temp,..cut heat off and the engine temp goes back to normal and heat barely gets even remotely warm. I have changed the thermostat,flushed the radiator and changed antifreeze,can it be something besides heater core before I tackle that job?
Sounds like you have a defective thermostat, make sure it is the proper temp for your application.
Check the hoses going to the heater core. (Check when truck is at operating temp). Are both hoses hot? If so core is ok. Is one hose hot and the other cold(or much colder than the other)? Heater core is stopped up. Are both cold or Luke warm? Coolant system issue. Low coolant, wrong or faulty thermostat or air in the cooling system.
Replace the water pump. The fins are eat off of the inside causing no heat.
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