Temperature Question

[pdpdrummer989]

Hello!
First time posting and just have a really quick question! I have a 2000 saab 9-5 and in the winter the car will heat up to where it is supposed to be and I will have a good amount of heat. When I start driving the temperature gauge starts to drop and I lose heat and my car will blow cold air and will only heat up again when I stop driving and waiting a few minutes. Since most of my travel to work is interstate driving it is important to me to have heat! I have been researching and from what it looks like I need to replace the thermostat (or at least start with that) but wanted some other opinions just to make sure I am starting in the right place! Also what thermostat and coolant would you all suggest?
Also I have run the test on the unit (holding auto+0ff) and get error code 1 on the left and 21 on the right which when i looked it up said something about a software flash.

[walawala]

i think you got it right that the thermostat is stuck open. They recommend to use original ones only. I've used a cheaper OEM before, but the rubber seal failed and started leaking from there.

[Mike Brennan]

Your Saab uses green coolant