To start off I have a 2005 Titan with 186k miles that I have had about 3 months. In this time I have dealt with the fuel pump issue, maf sensor issue, catalytic converter issue, shifter linkage issue, and now this.ome has me beat. It is overheating only when driving. As I type this I am driving a 500 mile trip from Louisiana to Branson Missouri with the heat on which is keeping temp at normal temp. My issue started as a radiator leak, but was not running hot, when I changed the radiator the radiator cap, not expansion tank cap, started leaking, but was still not overheating. Once I changed this and got the system sealed my overheating problem started. I had the system bleed and it stopped overheating for maybe a day, then the problem came back and I noticed the fan clutch was out, while changing this I decided to change the thermostat and all 3 hoses since they were soft beings they were 10 years old and kinda spongy. After this overheating was still occurring so I changed the water pump and ran a hose through the heater core which showed no signs of being stopped up. I am lost on this one. Runs fine with heat on with heat off it runs hot almost immediately. When it gets warm I can kill it let pressure off expansion tank, when I do this coolant rises and then will reenter system within seconds which makes me believe its the thermostat,but I have changed that 3 times and now I have a failsafe in. I am lost on this. I love my titanand really wantt this problem fixed. I am wondering if the engine coolant temp sensor would throw a code if it went out and if the vehicle is even really running hot. I am debating changing it just to see, I mean whats $25 compared to the $700 I have put in the cooling system. PLEASE ANY HELP WOULD BE GREATLY APPRECIATED!