Oil Pressure Drop at Idle and Check engine light coming on NEED HELP
 

Hi everyone, new to the forum, going through some issues that hopefully someone here can help me out with. Ok lets get started.

Symptoms: When truck is at Idle oil pressure goes to 0 and check engine light comes on only AFTER TRUCK IS WARM, WHEN TRUCK IS COLD OIL PRESSURE READS REGULAR. Then upon revving the engine oil pressure returns and check engine light turns off. All this started AFTER me replacing lower intake manifold gasket.

Well it all started. I have a 1990 F250 with the 351w fuel injected 5.8. It all started with my lower intake manifold gasket going out and spewing coolant everywhere, i hear its kind of a common problem with this engine. So i stripped her down took off the upper intake, throttle body, distributor, yadda yadda yadda, everything down to the lower intake manifold. Pulled that off and replaced the gasket how the book told me to do. Put her all back together and fired her up.

She ran perfect and no leaks that I could tell. Ran her for a while around town and back home with no problems....... until I got home. As I was pulling into the driveway and pushing in my clutch when the engine idled down i notice my check engine light suddenly comes on and my oil pressure gauge drops to 0. Then I hit the gas and revved her back up my pressure would return to normal and the check engine light would shut off, but soon as I let off the gas I lose my oil pressure and the light comes back on.

So basically at an idle I have no oil pressure and a check engine light on but when i rev up the engine my oil pressure returns and check engine light turns off. Hmmmm what can this be, I'm kind of feeling like i probably screwed something up in the installation process. Does anyone have any ideas? Could really use some help on this one, I hope I didn't totally screw my engine. :'(:'(:'(

Did you change the oil after you replaced the intake gasket? If not, you most likely have antifreeze in the oil, which wiped out the engine bearings, leaving no oil pressure at idle.

Your pressure will go up to normal when revving the engine because the gauge is basically an oil pressure light. Anything over somewhere around 7 lbs will cause the gauge to go about halfway into normal.

Sooooo basically i spun a bearing and my engine needs a rebuild? That really sucks.

Antifreeze will wear the coating off the engine bearings. Get a mechanical gauge and verify the oil pressure is low before you do anything drastic. There is a chance the oil pressure sending unit happened to go bad. But, if you didn't change the oil after you replaced the gasket, do it before you start the engine again.

You may be able to get by with some 10w40 oil.

Well Ill try an oil change tomorrow and post what happens.... thanks for the input yardbird its appreciated. So frustrating spent all day busting my ass and now this /:

That dash oil gauge is just a dummy gauge. Either on or off.

As yardbird said, put a real mechanical gauge on and see what the psi is.

If the engine sounds quiet, no rattles or knocking, I'd call it day and drive it daily.

maybe not. you may just have a bad sending unit. the stock "gauge" is really an idiot light. either on or off.
put a real oil pressure gauge in the truck and see what it is doing.

All good ideas... thanks for the help everyone I'm working now but after work I'll go tinker around some more after work