NOTE: this answer is describing the location of the engine coolant temperature sensor - NOT the coolant sensor in the reservoir that warns when the level gets too low.
The coolant temperature sensor is located directly adjacent to the thermostat housing. The thermostat housing is what the upper radiator hose (toward the right side of the engine compartment) connects to. You do not have to replace the reservoir to replace this part, but leaky coolant reservoirs are a common problem on this model.
The only place available is the coolant reservoir.
The low coolant sending unit is integral to the coolant reservoir. I just called two dealers, they were both $117 for the reservoir(!!). Before replacing, try cleaning the contacts on the connector, and also try cleaning the sensor in the reservoir with a long bursh before spending that much money.
On a 2002 Mercury Sable : The engine coolant reservoir is at the front of the engine compartment , on the passenger side of the engine compartment ( the engine coolant reservoir has a thread on cap on it , that is your pressure cap / radiator cap )
Is it leaking from the side by the coolant reservoir?
On a 2002 Mercury Cougar : No , the thread on cap on your engine coolant reservoir is the pressure cap / radiator cap
The thread on cap on your engine coolant reservoir is the pressure cap / radiator cap on a 1999 Mercury Mystique
On a 1996 Mercury Sable : The thread on cap on the engine coolant reservoir is the pressure cap / radiator cap
No , the thread on cap on the engine coolant reservoir is the pressure cap / radiator cap
I was looking at a picture in the 2003 Mercury Grand Marquis Owner Guide and it shows the power steering fluid reservoir at the front of the engine compartment between the engine coolant reservoir and the engine air filter box
On a 2003 Mercury Sable : The thread on cap on the engine coolant reservoir is the 16 PSI pressure cap / radiator cap
On a 2007 Mercury Milan : The thread on cap on the engine coolant reservoir is the pressure cap / radiator cap
On a 2002 Mercury Sable : The thread on cap on your engine coolant reservoir is the 16 PSI pressure cap / radiator cap