Turn fuel cap until it clicks. Then you will no it works with out any leaks. If the fuel cap is leaking, have the cap pressure tested, I believe it should hold to 26.* p.s.i. Replace fuel filler cap if needed.
According to the 1998 Ford Taurus Owner Guide : There was not a flex fuel version of the 3.0 liter " Vulcan " engine offered on the 1998 Ford Taurus
On a 2003 Ford Taurus : The 3.0L " Vulcan " V6 engine ( and the flex fuel version ) have ( 1 ) timing chain The 3.0L " Duratec " which is a Dual Over Head Cam design has ( 2 ) timing chains
I was looking at the 1999 Ford Taurus Owner Guide and it doesn't show a flex fuel version of the " Vulcan " 3.0 , V6 engine for the 1999 model Ford Taurus
The 2013 Ford Taurus runs on flex-fuel (unleaded/E85).
The 2014 Ford Taurus runs on flex-fuel (unleaded/E85).
On a 2003 Ford Taurus : The 3.0 liter " Vulcan " V6 engine ( and its flex fuel version ) Which is an Over Head Valve / pushrod design engine The 3.0 liter " Duratec V6 engine ( which is a Dual Over Head Cam engine design )
On a 2003 Ford Taurus : The 3.0 liter " Vulcan " V6 engine ( and flex fuel version ) have ( 1 ) timing CHAIN The 3.0 liter " Duratec " DOHC , V6 engine has ( 2 timing CHAINS , one chain to each cylinder head
According to the 2003 Ford Taurus Owner Guide : With engine oil filter change : The 3.0 litre " Vulcan " V6 and it's flex fuel version take ( 4.25 litres ) The 3.0 litre " Duratec " DOHC , V6 engine takes ( 5.2 litres )
A 2003 Ford Taurus was offered from the factory with either the 3.0L " VULCAN " V6 engine ( and the flex fuel version ) which are OHV ( Over Head Valve / pushrod design engines ) or The 3.0L " Duratec " V6 engine which is a DOHC ( Dual Over Head Cam ) design
On a 2003 Ford Taurus : The 3.0 liter " Vulcan " V6 engine ( and the flex fuel version ) have one timing CHAIN The 3.0 liter " Duratec " V6 engine has two timing CHAINS ( one chain to each cylinder head )
According to the 2003 Ford Taurus owner Guide : With engine oil filter change : The 3.0 litre " Vulcan " V6 engine and its flex fuel version take ( 4.5 U.S. quarts ) The 3.0 litre " Duratec " V6 engine takes ( 5.5 U.S. quarts )
On a 2003 Ford Taurus : The 3.0 litre " Vulcan " V6 engine ( and its flex fuel version ) is rated at ( 155 horsepower ) The 3.0 litre " Duratec " V6 engine is rated at ( 200 horsepower )