I've been driving my '88 4Runner with 22RE for almost 9 years and the heater has never blown very hot. It's gets warm, but I'm about to move to a colder climate so I need it to start working properly.

New thermostat didn't help. I haven't looked closely but do the coolant hoses that run through the idle air control valve or anywhere else bypass the thermostat? (The IAC valve has also never worked in the time that I've owned the vehicle, so it's got no choke either.)

There was some corrosion in the cooling system that warranted head gasket replacement before I bought the truck. I can see some hard white deposits in the radiator hose pipes, etc., still. The hoses going into and out of the heater core seem to be about the same temperature and seem pretty hot, but I don't know what they're supposed to feel like. I even bypassed the valve on the firewall to make sure it wasn't restricting flow. Nothing seems to get the heater to blow hot.

If I do need to replace my heater core, must I remove the evaporator or is there a way to do it without discharging my air con?

Thanks!