when I drive my car my heater works until I stop and then it just blows out cold air. As soon as I excellerate again it heats up and blows hot air. What do you think the problem is. I have a mitsubishi 2001 eclipse spider. Someone told me it is the water pump going out. And someone told me it could be a vaccume hose. Or maybe the thermostat. I dont want to pay to have the waterpump replaced if that is not the problem.
I doubt if it is the thermostat, but it may well be a vacuum issue or it may be low coolant or that water pump. Since you have a 2001 my guess is you have a vacuum hose problem as the water pump should be OK unless you have a lot of miles on it or you have not taken care of the coolant properly.
I doubt it is the water pump. The engine will be overheating if that were the problem. I suggest it is a bad thermostat. A lot of these Japanese cars, even econo-boxes, have actual engine temperature gauges in them, not idiot lights. Is the gauge reading on the low side, high side, or middle? I suspect it is on the low side. This is an indication of a bad thermostat.
You might want to check the coolant level in the cooling system.
If the coolant in system got low enough where air got entrained in the cooling system, this air can end up in the heater core at idle conditions. When this happens, there is no heat transfer from the heater core into the passenger cabin. When the RPM’s of the engine are brought up, the water pump spins fast enough to push the air out of the heater core and you get heat.
Have the cooling system purged of air to make sure this isn’t all that’s wrong.
Tester
Have you ever removed the radiator cap (engine cool) and checked the coolant level? Do so, now. Fill the radiator. Move over to the “coolant reservoir tank” (overflow bottle). Look at the tube inside the tank. It may be bent, or have a blocked opening. This condition can prevent coolant from going back into the radiator when the engine cools. When the engine gets hot (normal hot), the coolant expands and some is forced to the coolant reservoir tank. Each expansion forces a little (pint?) into the tank, so that the tank fills (maybe overflows), and the radiator empties. This is covered by a Mitsubishi Technical Service Bulletin TSB-02-14-001.