temp gauge goes hot then cools and cabin heat does the same. changed thermostat, water pump, ect sensor and it still happens. what else could it be? 2001 chevy venture.
How hot and how cool?
sometime in the red. and heater blow outside air temp.
Could be a bad temp sensor could be an air pocket in the system or a clog somewhere. Those are the most common for that situation. If its like my buddies 01 sierra there is a little orifice in the hose going to the heater core to prevent chunks of contaminate getting into the heater core. The orifice was clogged after flushing the heater core in reverse it worked fine.
Not to scare you, but I've seen if on your series of engine. If something with a water jacket is leaking and introducing air to the system it tends to do this. Try burping the system. If it happens still after that sensors are worth checking but you may have something like bad intake gasket or head gasket. Not trying to jump the gun, still try simple stuff first.
98-03ish only reason I didn't mention the dexcool intake gasket issue is because he didn't mention coolant loss or milky oil.
flush the heater core
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