Toyota Repair: very little no heat, heater control valve, resivoir

Question
I have a 91 4-Runner 3.0L no ac. Lot of history here but not many facts, I bought it used drove it about a 1 1/2, before I got it appears the engine had a major coolant explosion, radiator was new and couple hoses, since then put a new rebuilt motor in it and the heat was diminishing prior to that, drove it and didn't think much of it. Now cooling system gets up to temp, the upper hoses hot that lower hose cold. So I replaced the t-stat thinking it was stuck closed, doesn't appear that it, still blows cold in all settings, Ive been told could be heater control valve, probably the heater core, coolant seems to boil out the resivoir after my long 38 mile drive to or from work. Spoke with Toyota mechanics, Im in the automotive business too but not getting much help , could you offer some advise...Thank You. Vehicle has 249,000 miles

Answer
You're overheating it.
Better replace the thermostat again (Alot of times they're replaced with alreayd broken units, or isntalled incorrectly - trust me)
Replace the pressure caps, make sure the radiator is not clogged, and check that the water pump is working - no corroded fins.



Regardless of heat/no heat. It's boiling over... You can run without heat, but that piece of shit engine will roast a headgasket in a heartbeat if it's hot & the coolant cools back down to a normal temp before it gets back to the sensor.

Yeah. You can check that the valve swaps over, and that the heater core loop is not plugged.