Yes, they are identical
For a 1991 Ford Crown Victoria : " regular " unleaded , 87 octane
In the gas tank.
4
The thermostat on a 1991 Buick Skylark is located near the engine. To find the thermostat, follow the top radiator hose directly to the thermostat.
Yes, both model years are AOD transmissions.
You can find the 1991 Dodge Shadow thermostat in the thermostat housing. The thermostat housing will be on the front of the engine.
According to my Chilton's book : For a 1991 Ford Crown Victoria ( 5.0 / 302 and 5.8 / 351 ) With engine oil filter change ( 5.0 U.S. quarts )
Try changing the thermostat.
10 degrees advance
Often in the owners manual is where i found the one for my 1991 Crown vic. Hope you have your manual?
The best is to buy a new one.