The thread on cap on your engine coolant reservoir is the pressure cap / radiator cap
Probably in the housing at the engine end of the upper radiator hose
The 2001 Ford Focus has an inline 4 engine.
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The 2001 Ford Focus has a 2.0 L base engine size.
The 2001 Ford Focus's engine produces 130 hp @ 5300 rpm.
The 2001 Ford Focus's engine produces 135 ft-lbs. @ 4500 rpm.
On a 2001 Ford Expedition : The thread on cap on your engine coolant reservoir is the pressure cap / radiator cap
In the top radiator hose fitting opposite the radiator, on the engine.
on the radiator fan
Follow the top radiator hose to where it meets the housing that goes into the driver's side of the engine, the thermostat is in that housing.