You might have bad actuator that opens and closes airways.
Have you checked your thermostat?
Hi have you checked the radiator for blockage if it is blowing water back out the radiator this could be the problem.
This question is not complete. . Need to know if you've replaced radiator, thermostat, hoses etc. Are you asking this question *after* yo checked the thermostat, changed, added or drained the system?
Bad thermostat maybe?
You've checked and replaced everything except for the water pump...I recommend replacing the water pump every time you replace the timing belt.....
im having the same problem with my 1994 I've replaced the heater core,thermostat,radiator,i checked the coolant, and it's not over heating or nothing and still no heat lol
The radiator may be plugged. Take it to a radiator shop.
If you have an old ISUZU Trooper, the radiator thermostat may be not working. Therefore, it will not let cool water from the radiator into the hot engine, even if the radiator is full. Have the thermostat checked and replaced, if necessary. Good Luck
Have your injectors checked or changed, burnng to much fuel
you may want to have the heating core checked!!it might be clogged up and not letting any hot water passing thru.
thermostat probably stuck open needs to be checked or replaced
Intake manifold gasket leak? (Never heard of a heat sensor). Many possibilities.