My truck:
2000 Mazda B4000, 4.0L V6, 5spd, 4x4, extended cab. It won't heat up. Before, I remember when I started it, and it warmed up, the temp gauge would stay at just under 1/2 way, I had constant heat, etc. Laitly I have noticed when I start it, the temp gauge goes to about where it used to, then falls, then it will go about 1/3 of the way, then fall. It will keep doing that, for a bit, then it will level out depenting on how hard I am working the motor. If I do a hard hill climb, it will come up to about where it used to be (about 1/2 way) but as soon as I am off the gas it drops right back down to just above the C mark, or even under it!
At first I sorta thought it might just be the sensor/gauge, but the hot air changes with the gauge, making me thing that it's the thermostat.... Last night I was coming home loaded with wood from the shop (about an hour's drive) it was a little below freezing, most of it is flat road, 5th gear doing about 100km/h not pushing it that hard, the heat was all the way to "hot" and it was a nice temp in the cab. Going up a small mountain pass (about a 15 min climb, 4th gear, still holding 100km/h) the temp gauge was up to about normal(middle of the gauge) and I had to turn the heat down 'cause it was getting way to hot in the cab. On the way down (about 10 min, 4th gear, little or no gas pedal) the temp drops to under the C (about where it normally is when you start it cold) and I got no hot air. I realize that it should change a little bit going up/down and such, but it's not holding temp like it used to. Can someone confirm my Thermostat thought, and recommend a thermostat that I should get, or just goto the Ford/Mazda dealer and pick one up? Thanks! ~Brian