Ruiner2000

Have an 87 Formula I bought during Summer that was restored. Car sat for 3 months and recently tried to take it out but heat not working properly. The diverter valve is functioning. I have an 83 TA as well as a 91 Bird v6 to sort of compare to, and the car is running really cool. If I pull the fuse for the cooling fan and let temps get up to 220, I get some heat out of it, but nothing compared to the other vehicles. Under this scenario I was thinking possible blockage in the core?

The other odd thing is the car runs extremely cool and the electric fan turns on and off with low temps. All of the sensors are new but I'm not convinced the one controlling the fan is good because it cycles on and off with temps just above 120 or so, but well below the middle line between 120 and 220. For example, on my 91, the temps will get close to the 220 mark (not quite there), but the car cools down to about that line in between and then starts over. This 87 Formula in question will not see temps above that mark in between 120 and 220, and when driving, temps drop to in between the 120 and that middle mark. Is that mark in between supposed to 160 or 180? I realize that the gauge may not be 100% accurate, but with the car idling it will get to that mark and I have warm air coming out. But once I start driving the car cools below it and then cool air comes out. The only way to get a decent temp out of the heater is to pull the fuse and let it go to 220, but even then it's not HOT like the 91. The 91 is hot way before any of this and works as a heater should.

I hope this blather makes sense to somebody. Things I am considering to look at are.
Heater core blockage.
Thermostat.
Temp sensors.
This was all supposed to have been replace along with new engine and everything under the hood, but who knows.

1987L69

I would start with the thermostat. I know a friend that has an 86 Iroc and he was going to replace the fan temp sensor and every one he got would kick on very early. I do not know his fix for this issue though. I would make sure that your vents are working properly as well, the correct doors behind the dash open and close based on what your controls are calling for. that could be a nightmare because of the "restoration"

Ruiner2000

Sounds like a good place to start. All of the controls work properly and are functioning as they should. There is plenty of airflow and air is coming out of the vents they should when called for.
Thanks.