[Brwilliam24]

Hi, any advice is appreciated! I have a 2005 Titan with 180,000 miles. After 30 minutes of driving the temp spikes to 3/4 mark. I turn on heat but it blows ambient temperature air. If I rev the engine or shut off and turn on the temp suddenly drops to midpoint and starts blowing heat. When engine overheats I get no heat then at same time engine temp goes normal and heat resumes. I've changed thermostat twice, had two separate garages tell me my fan clutch wasn't engaging properly at higher temps, so I replaced twice! I've flushed cooling system twice and bled out air. Thing maybe radiator blockage but took off upper and lower hoses and water runs out of radiator fine. Thanks again for any advice!

 

[Kronos1965]

Hi, any advice is appreciated! I have a 2005 Titan with 180,000 miles. After 30 minutes of driving the temp spikes to 3/4 mark. I turn on heat but it blows ambient temperature air. If I rev the engine or shut off and turn on the temp suddenly drops to midpoint and starts blowing heat. When engine overheats I get no heat then at same time engine temp goes normal and heat resumes. I've changed thermostat twice, had two separate garages tell me my fan clutch wasn't engaging properly at higher temps, so I replaced twice! I've flushed cooling system twice and bled out air. Thing maybe radiator blockage but took off upper and lower hoses and water runs out of radiator fine. Thanks again for any advice!

Radiator Cap may be bad!

If not...
Water pump?
Obstruction?
Head gasket going bad?

 

[electricjohn]

A small unnoticeable radiator leak cause the same problem for me. Are you losing coolant?

 

[HRTKD]

It could still be air in the system. The lack of heat coming out when the heater is turned on should be a clear signal that something isn't circulating properly.

Describe how you bleed air out of the system.

Have you verified that the system will hold pressure?