My 2007 V6 Tacoma is overheating, I have done just about any test imaginable, replaced the thermostat, water pump, did many other checks, incl. chemical test for gas residue in the coolant system etc. All tests come back negative. It looks like the head gaskets are not leaking.
The only other thing that comes to mind is that the heater core might be a problem. How do I test that?