oil pressure problem

Z

zbird1

Registered User
I have a 90 sc when i start it the oil pressure is fine but after it heats up at idol the pressure drops all the way down to zero. if i keep the rpm's above 1000 or while i'm driving it stays at normal pressure. I have changed the oil many times and have changed out the oil pressure sending unit but it still only does it after heating up. if it was internal wooden it do it at start up or all the time? it's been like this for about 6 months but as long as i put it in neutral and keep at 1000 rpm's it's ok. can a oil pump get weak? has this happend to anybody else.:confused:
 
You need to test the pressure with a manual gauge. The stock gauge and sender are pretty much worthless crap and will show the same pressure reading on the gauge if you have 10 psi or 60psi.

If pressure really is low, it usually caused from wear to the bearings in the motor. Pressure will always be higher on a cold motor, because the oil is thicker.

David
 
will try that this weekend and see what happens. what should the oil pressure be on a manual pressure gauge
 
Its probably time for some thicker oil, that might prolong it. I have a 300K mile F150 with 5.0 that does the same thing. After you really heat it up it goes way low at stop lights, but fine everywhere else. I just run 20W50 in it all the time now and its much better.
 
ok this is what I have. I hooked up manual gauge and it started out cold at 60psi after it warmed up went down to 15psi but I let run for about a half hour more and it went down to about 7psi so then I got in the car and put it in gear with my foot on the brake and it bounces from 0 to 5psi and when I put it back in park it goes back up to between 7 to 10psi. can this be a bad oil pump or is it something internal please let me know.
 
zbird1 said:
ok this is what I have. I hooked up manual gauge and it started out cold at 60psi after it warmed up went down to 15psi but I let run for about a half hour more and it went down to about 7psi so then I got in the car and put it in gear with my foot on the brake and it bounces from 0 to 5psi and when I put it back in park it goes back up to between 7 to 10psi. can this be a bad oil pump or is it something internal please let me know.
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Tell us more about the car. How many miles are on it? Does it make any noises when it's warm and in gear, or when you're driving it around? While I'm certainly not an expert, I wouldn't think you would see 60 psi at anytime regardless of oil temperature with a bad oil pump. To me this sounds like worn rod bearings, which will increase tolerances and lower oil pressure, especially under load (such as putting the car in gear with your foot on the brake.) Often with that kind of wear a light knocking can be heard at idle or at low RPM's under load. While throwing some heavy weight oil in it could buy you some time, worn rod bearings will eventually spin, and that would likely require a new crank.
 
I had blown a haed gasket at 117,000 crack the block and head in the same place so I scraped that motor and got a long block out of a 93sc that had been in a head on wreck with only 65,000 miles on it when I was putting this motor in I change everthing (gasket,timing chain,ect) but when I took the timing cover off it was in three peices so the motor took a pretty hard hit so I swithed everthing over from the other motor and put it in my car. I drove the car maybe 2000 mi before the oil pressure started going bad ( but not this bad) but the car has 128,000 so that motor should have about 76,000 on it now but I have not drove it for the last year because of the oil pressure but I start it from time to time and take it around the block. (short trips) it makes no noises or rattles and idles smooth and sounds normal when your driving it.every once in a while when you put the hammer down it almost sounds like you can here the lifters chatter but I'm not sure. I just don't know what to think.
 
pressure at 2500 rpm is about 35 psi and it has 5w30 in it now and will it hurt it if I put 15w40 in it ?
 
The bearings are shot. I would recommend replacement before the crank is damaged more than it already is. Be sure to check clearances before you put it back together. An SC should have 30psi or more at hot idle and 60+ above 2500rpm.

That "lifter rattle" you hear is rod knock. If you keep driving it the motor will be trash. It's too late for a heavier oil trick.
 
zbird1 said:
pressure at 2500 rpm is about 35 psi and it has 5w30 in it now and will it hurt it if I put 15w40 in it ?
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the oilpressure spec that i found on a ford technical website, is 40-60psi at 2500 rpm @ operating temp. 35 psi is just slightly below it. 5w30 does thin out alot when it gets hot. personnaly i would run 20w50 with some oil supplement full of additives such as zddp and molybdenum.one such supplement, GM EOS(engine oil supplement) can be bought at a GM dealer by the quart.probably one of those quarts, and 4 quarts of 20w50 and see how she holds up.
 
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