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Discussion Starter · #1 ·
Hey guys, I just bought a slightly modified 1991 Mustang GT. So far as I have learned from the forums, it is running as it is supposed to. It also has auto-meter gauges installed that I am hoping are accurate so here is my question. When my car is warming up when I first start driving around, the oil pressure is around 40-45 psi. Once it warms up and while driving it drops down to around 25-35 psi and stays there more or less. When I stop, it drops to around 18 psi. Is this normal or is this the sign of a pending rebuild? Also, is the oil sending unit and the oil pump two different things?

Is there the possibility that because I have a Ford Racing E-Cam installed that the idle produces could cause the pressure to drop?

I am pretty well versed in understanding cars put I have never owned a vehicle before that had, in my opinion a few inferior parts installed from the factory. From what I have read here, the water and fuel pumps should be upgraded as well as the oil sending unit. If you read the description of my car I think most of the major parts have been taken care of with the exception of the cylinder heads and the oil sending unit. Thanks for your time!
 

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at idle around 25-45 psi, at 2k rpm and higher around 45-65psi, sound like a rebuild or if your luckey maybe just an oil pump.
 

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If the car's pressure drops after it warms up you probably have to replace your engine bearings-aka rebuild it. This condition occurs when the metal expands in the reciprocating assembly(crank, rods, etc) and causes the gap from the worn bearings to increase thus decreasing the pressure. My 1988 GT has the same problem only much worse the pressure drops to 0 after about 10 minutes of idling and only registers single digits when you rev the engine. My engine is undoubtedly shot. I've never heard of upgrading your sending unit-that's just the switch that sends signal to your oil gauge. If it doesn't work it reads nothing all of the time. I think you're confusing the oil pump with the oil sending unit(sends current to gauge) which is also called the oil switch. Your cam won't make a difference in oil pressure. It is possible your oil pump is worn instead of the bearings but I doubt it. Though maybe worth a try to replace....
 

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Hey guys, I just bought a slightly modified 1991 Mustang GT. So far as I have learned from the forums, it is running as it is supposed to. It also has auto-meter gauges installed that I am hoping are accurate so here is my question. When my car is warming up when I first start driving around, the oil pressure is around 40-45 psi. Once it warms up and while driving it drops down to around 25-35 psi and stays there more or less. When I stop, it drops to around 18 psi. Is this normal or is this the sign of a pending rebuild? Also, is the oil sending unit and the oil pump two different things?

Is there the possibility that because I have a Ford Racing E-Cam installed that the idle produces could cause the pressure to drop?

I am pretty well versed in understanding cars put I have never owned a vehicle before that had, in my opinion a few inferior parts installed from the factory. From what I have read here, the water and fuel pumps should be upgraded as well as the oil sending unit. If you read the description of my car I think most of the major parts have been taken care of with the exception of the cylinder heads and the oil sending unit. Thanks for your time!
ford 302- 55-60 cold startup, 35-45 warm at approx-1800-2000 rpm, stop and go warm 15-45, idle warm 15-25. these #s vary according to engine oil weights and viscosity. normal 15 to 20 psi drop should be expected when the engine reaches normal operating temps and the obvious engine wear should all be taken into consideration.
 

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Discussion Starter · #5 ·
Excellent information guys thanks!!

It is always good to get a quick reply on these questions. Thanks for your help and time!
 

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Glad they helped you out.
 

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you never said grade of oil or if it is dirty? does it smell like gas?..it's also poss. you could have some trash/sludge in the pickup...
 

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Discussion Starter · #8 ·
Oil info

When I first bought the car, about two weeks ago, I had a full synthetic oil change and it now runs Mobil 1 synthetic 10W30. There could be some sludge left over in the engine from the previous owner after my change but hopefully after my next oil change, any remaining old oil will be removed.
 

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an oil change will not unclog a partial plugged screen..

are you using a mechanical oil pressure gauge?
 

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Discussion Starter · #10 ·
Oil screen?

Is the screen you are talking about part of the oil pump or part of the sending unit? I had just decided to run synthetic because many people on this website recommend it, I didn't think it would clean anything out but instead provide better lubrication.

Also, I don't know how my Auto-Meter oil pressure gauge works as it was already installed in the car when I bought it. I am assuming that it hooks into the spot where the factory oil pressure gauge would plug in. I am guessing mechanical. The nice thing is that I have driven the car on some longer road trips and the pressure doesn't drop below 35 psi when I am going highway speeds.

When I come to a stop, or while letting the car idle, the pressure stays at 20 psi. I also had a Jeep Cherokee that had done that since the day that I bought it. The pressure would go up and down depending if I was on the throttle or not.

After warm-up, on a healthy engine, should the pressure be the same whether the car is at idle or at highway speeds? I would imagine that the pressure would go up while running the car at speed. So long as I have a decent amount of pressure I am not going to worry for now.
 

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The rule of thumb I've always used (at least with Chevy motors) is that 10psi per 1000rpm is fine. I would be concerned if oil pressure at warm idle was lower than 15psi or so (assuming a ~700rpm idle), but as long as it goes up with rpms, and never drops below 15psi, you should be fine.

Just for reference, in my '94 Trans Am, my warm idle pressure was only about 10psi, but it would rise with rpms. When we pulled the motor for a few upgrades, all of the bearing clearances still checked out. That motor had about 120,000 miles on it, many of which were hard miles. Reduced oil pressure over time is a fact of life.
 

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Discussion Starter · #12 ·
Thanks!

It is always good to get the information that I do on this forum. I will keep an eye on the pressure and if it really starts to drop, I will start saving up for a rebuild or rebuilt motor.
 

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Keep us informed.
 
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