i've had this problem for like 5 months now... when i start up the car, the oil pressure reads no lower than 15... but when i drive it for a while, adn the car warms up... it usually goes down to zero!!! the first time this happened, i pulled over immediately and checked it out... but i have never heard any knocking or anything like that... is it possible that my gauge is messed up???... let me know if this has happened to anyone else! thanks

 

if this is the factory electric gauge, it is more than likely the trouble. they aren't very reliable. to be sure, go get a mechanical gauge at the parts store and see what it reads.

 

mhmmm alright then, i'll do that... thanks

 

Well.. reliability is questionable. After 12-22 years of service, things are bound to fail once in awhile.
Generally, the problem is the oil pressure gauge sending unit. I had the same problem with my firebird and camaro. They broke in different way (because of different senders) but, still the same gauge problem (slow bleed off of pressure).
The sender on the '89 is going to be a combo oil sender/switch (iirc) and located right above the oil filter.
Just for kicks, check to make sure there isn't one (sender) next to your distributor (drivers side of it), I don't remember offhand what year the sender was changed to the combo. A quick visual will tell you yay or nay on the one next to the dist. though.

 

go buy a $10 mechanical gauge hook it up,,screw it in where the stupid,,,old sensor is ,use it to check when the engine is hot,,,,,,,,,,,,,,dont waste time

 

thanks a lot for the info guys... i think i'll get the mechanical gauge, and then change the sending unit... thanks again!