I’m sure this has been asked 1,000 times but I found nothing in the search for it.“Low coolant level” message every time I start my 2001 Grand.I’ve heard it’s a very common problem with those coolant reservoir float switches so I’m gonna replace it and see what happen.s Question is if the radiator is completely full should there be a certain level of fluid in the reservoir as well or doesn’t it matter? Thanks.

 

Yes, there are two marks on the side of the reservoir. The coolant should be maintained between these because, when the engine gets hot, the coolant expands and is released by the radiator cap and goes into the reservoir. when it cools down, it is sucked back into the radiator. If there isn't enough coolant in the reservoir, it will suck air into the radiator. If there's too much in the reservoir, it can be lost from the reservoir overflow vent when it gets hot. There are 2 pressure control valves in the rad cap. One holds high pressure to increase the boiling point of the coolant, and the other opens at a very low vacuum to allow coolant to re-enter the rad.