Toke, you need a new thermostat. They are supposed to open at 87degrees, when they get old they either open at 87 as they should but then fail to close and so the coolant gets cooler and cooler or they just open at a lower temp and the coolant never reaches temp. You just need to watch if the coolant goes over 90 then the thermostat is stuck and will likely seriously over heat and could damage the HG.