Oil Pressure Light Comes On

vs1957 · July 8, 2012

1992 ls 400 oil pressure light comes on for about a minute than goes off while driving even though the oil level is at full. Is that normal?

billydpowell · July 8, 2012

It is possible... sometimes while driving at highway speeds the oil is pumped up to the top of the engine, meaning the oil is low in the pan, and that would cause the light to come on... and then go off as the oil returns to the pan. I hope that is not your problem, because that would mean your engine has sludge in it..... removing the valve cover would show this...

landar · July 8, 2012

Well it most definitely is not 'normal'. However, for a '92 it is not out of the question. The problem typically occurs while the engine is hot and idling. You step on the gas, the RPM's increase(along with the oil pressure) and the light goes off. Usually this condition is the result of an improperly working oil pressure sending unit. Simply replacing the sensor with a new one will solve the problem.

I say 'usually'. And if you have lived a clean, honest life, it will be as simple as the oil pressure sensor. If not, there is a remote possibility that it could be a weak oil pump or loose bearing clearances(primarily main bearings). As Billy mentioned, excessive sludge can also clog up the system, restricting oil passages and cause the symptoms ...but, while reported on some V6 Toyota engines, it is not at all common on the the LS V8 engine, especially if the oil has been changed within recommended intervals.

If it were mine, I would want to hook up an oil pressure gauge to the system (easy to do) and get an actual oil pressure reading. That will tell you if your problem is simply a faulty sensor or more major issue. Of course, you could also just screw in a new sensor and if that fixes the problem, call it a day.

vs1957 · July 8, 2012

Thanks for your comments. Because I know the previous owner of the car I am going to assume there is no sludge build up because they kept the car well maintained and had the oil changed regularly.

I might try to change the oil pressure sensor and see what happens. Can you give me an idea of where it is and if there is anything I need to know about changing it? Does the oil need to drained before doing this?

If that does not work can you tell me how to hook up an oil pressure gauge? And can you recommend any brand in particular.

Thanks for all your help.

landar · July 8, 2012

The oil pressure switch is 83530 in this diagram. It is screwed into the block in the location shown. If you do not feel comfortable replacing it yourself, seek out a mechanic. An oil pressure gauge can be purchased at most auto stores fairly cheap(<$30, most brands would be adequate) and you would remove the existing switch and just screw the gauge into the same hole in the block for a temporary reading. You should not have to drain the oil to do this. Just do NOT start the engine with the oil pressure hole exposed (ie: sans switch or gauge).

billydpowell · July 8, 2012

only problem:, oil pressure light comes on for about a minute than goes off while driving ... How are you going to know at what oil pressure the light WOULD come on?

It doesent seem to be a constant failure... guess I am not thinking right about this...

vs1957 · July 9, 2012

Thanks for all the feed back.

Billydpowell, you make a good point. I could put the pressure gauge on and not get a low reading since it only happens sometimes.

Might just look into changing the the pressure switch.

billydpowell · July 9, 2012

good idea, let us know how it turns out.

BentBrain · July 9, 2012

The OPSU generally fails in that it starts to operate erraticly. Never had one fail on the LS but on other cars with pressure needles on the dash. The. Redoes would start to flop all over the place while the car was running. Sometimes they would read real low and than normal or high. Never seen one just fail outright like reading no pressure all the time.