This article is from the Chrysler-Plymouth-Dodge FAQ, by Dr. David Zatz with numerous contributions by others.
() firstname.lastname@example.org had poor heat in his Lancer.
The temperature regulator door was not sealing well in HOT, letting cold
air bypass the heater core. He stuffed a 4-5mm by 12 cm piece of foam
in, closed the door on it, and unhooked the cable until Spring to keep
it in place.
If your radiator cap leaks or the hose to the CRS bottle leaks the
vacuum will be lost and it won't suck the juice back in. Blow on the
bottle to see.
Dennis Lippert notes: The temperature gauge will swing back and forth
until the entire system is warmed fully. This is because you keep
introducing "cold" coolant from the radiator into the engine, rapidly
cooling it. WHen the temp falls enough, the thermostat closes, and the
temp goes back up, repeating the cycle. This is due to a valve which
lets you get heat before the thermostat opens up. It keeps the warm
coolant in the engine *and heater* when the thermostat was closed.
Peter Galambos related: Fixed by flushing the system with oxalic(sp?)
acid (i.e. Prestone Super Flush). Now the heater works great and the
engine temperature changes much less. There was probably a restriction
even though the antifreeze looked fine; a lot of rust flowed out when