Heater not blowing hot air

Tiny
KCART
  • MEMBER
  • 1993 PLYMOUTH SUNDANCE
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 102,300 MILES
Not blowing hot air when car is warmed up and won't get above first line on temperature gauge.
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Sunday, February 24th, 2019 AT 3:18 AM

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Tiny
HEYMAN1104
  • EXPERT
Hello and welcome to 2CarPros. The most likely cause is a failed thermostat. It is stuck in the wide open position, which is letting coolant flow constantly and keeping the engine from ever getting warmed up. Normally, the thermostat should be shut and slowly open as the coolant warms up. This allows the engine to warm up but keeps it from overheating. A side effect of the thermostat staying open is that you'll have little to no heat. This is because the coolant runs through a heater core (basically a miniature radiator) behind the dashboard. The heater core is heated up, and the blower blows air through the warm heater core and then out through the vents, resulting in heat. I'm attaching AllData's instructions for removing and replacing the thermostat. They're not very well written instructions, but it's what we have to work with. The second image shows where your thermostat housing bolts are (circled in red). Also, here's a link to a YouTube video that's not perfectly on point, but it does explain a lot about the thermostat and how to bleed the cooling system. You might also take his advice and drill that hole in the new thermostat. https://www.youtube.com/watch?v=xjYufVTkBak

I'm not sure what size those bolts are, but if I had to guess I'd say either 1/2 inch or 9/16 inch. Basically, you'll take those two bolts off, pull the housing off, and pull the old thermostat out. Then, using a wire brush or something along those lines, you clean any excess old gasket crud off of the surfaces. This is vitally important so make sure that the surfaces are as clean and smooth as can be. Pop the new thermostat in along with any replacement gasket, and bolt it back together. Proceed to bleeding the system, as described in the YouTube video. Presto change-o, you're done and you have heat. Hopefully.

Go ahead and swap out that thermostat (available on Amazon or at any auto parts retailer) and let us know how it goes. If you have any other questions, feel free to ask. Thanks again for using 2CarPros.

- Harry

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Sunday, February 24th, 2019 AT 4:20 AM

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