1990 Mercury Grand Marquis Q&A
1990 Mercury Grand Marquis Question: 1988 mercury grand marquis oil light came on.
The oil pressure warning light is designed to come on when oil pressure dips below 3 to 7 psi. At that stage damage is being done to the engine so if it has been on for a while it is most likely a defective oil pressure switch which is probably less than $15 in parts and take a half hour to fit. - patrick mannion