Heat not working unless engine at higher rpms.
My car started this morning with the low coolant light on. When I went to add more coolant, I pressure cap was loose. I tightened it and light went off. I added about a quart of coolant. My heater is blowing cool air until I accelerate from a stop or am doing about 50 mph. Then I blow nice and hot like I am use too. Is this a thermostat problem? What else could it be?
This is a problem which unfortunately has shown up in a few of the 1992 Luminas. A common cause is a gummed-up thermostat. When this happens, the heat comes directly off the heads and flows down into the heater core, which then blows the heat into the cabin, which might explain your acceleration-only heating. One way to check and see if it's stuck opened is to let the car idle for about five minutes. Squeeze the upper radiator hose. If the thermostat is indeed open, you will feel water in the hose. If not, the problem is something other than your thermostat.
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