I have a 1990 Mazda B2600i 4x4, the truck works fine, but the operating temperatue of the engine is low the temperature hand just rised a little above cold even when she has been running for a long time.Once on the highway the temperature will rise to about half way but then as soon as i start slowing down the temperature hand will fall again. As i live in a cold enviroment it takes forever to get heat in the truck. I was just wondering if this is normal or do it indicate aserious problem.

 

To me, indicates a thermostat not closing. I'd replace the thermostat, cheap.

 

I Replaced the thermostat, still no difference, any ideas.

 

OK. Run engine for 20 minutes. Feel the two hoses that dive into the firewall in the middle(the heater hoses);BOTH should be pretty hot. If not, then engine is not reaching operating temperature, and that could be the problem. If BOTH are hot, good, as the coolant always flows through a B-Series heater core. So if hot coolant IS flowing through the heater core, either a cable-operated door/flap is not opening to let the air from the blower pass through the fins on the heater core. To check this out, you need to lie under the dash and look up at the console, get a helper to rotate the round control from Blue to Red, and back, and see what happens. I can't remember on which side that particular cable is; I had a cable slip off its control rod once. The control rod just moves a flap/door to direct the air flow. I'm assuming that your blower motor is operating, that you do get air flow out of the dash.

The levers direct where the air will exit from the dashboard, and it sounds like you have no heat exiting anywhere. Then report back exactly what your situation is.