Replaced the t-stat (97 2.7L) when I flushed and filled the radiator (bad gas mileage, low heater output; verified it was bad in hot water on the stove, also that the new one was good). Heat is better as is the MPG.
Read the Haynes manual about the coolant overflow reservoir and it states:"If the system pressure exceeds the cap pressure-relief value, the excess pressure in the system forces the spring loaded valve inside the cap off its seat and allows the coolant to escape throught the overflow tube into the coolant reservoir. When the system cools, the excess coolant is automatically drawn from the reservoir back into the radiator."
Huh?!? So it takes excess pressure just to move the spring to release coolant into the reservoir, but it magically can reverse its flow with the spring fully seated? I don't have a PHD in fluid dynamics but this makes no sense.
Missing winter in Minnesota