98 ranger 2.5 no heat

[holyford86]

I've been pulling my hair out over this, maybe someone else has run into it before, it had sat neglected for some time and the coolant was rather rusty when I purchased it a few years ago, I just did a drain and refill at the time and it was okay until this winter. I was noticing that I was getting pretty terrible heat in my truck, I flushed the cooling system and heater core until I had clean water coming out no matter which way I ran it through the system, refilled with new coolant and bled the system. Problem got worse, temp gauge would not move at all, or very little, tested radiator cap (it was bad) replaced it, replaced the thermostat because I figured it may have picked up some garbage when I flushed it out, it looked fine but swapped it out anyway. No change... Checked the live data and coolant temp in a 70 degree shop as around 135 degrees at idle, if I hold rpm at a steady 2800ish rpm I can get coolant temp up to about 180 degrees with a stock 192 degree thermostat. looked at mitchell online to see if maybe there was a bleed screw I was missing, to no avail. All of the hoses get warm, and there is a temp difference between the hoses going into the heater core, truck is not equipped with ac and does not have a bypass valve. When the coolant temp is hot I get good heat output from the dash vents too. All I can figure is that maybe the thermostat housing has distorted and the thermostat does not seal correctly.