Hey guys, I have a 91 lx with what I was told was a rebuilt 5.0l. When the engine is cold, I have about 40 lbs of oil pressure and wont go any higher. When it's warm it wont go past 35 lbs when I go though the gears, and under 15 lbs at idle. The factory dash gauge was barely registering so I bought an autometer electric gauge to come up with those numbers. The engine runs great, dosen't make any noise and dosen't smoke at all. Do you think the engine is done or is it the pump?
low oil pressure
- Thread starter trlprk
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The oil pump's definitely weak but the low idle oil pressure also indicates advanced bearing wear. You could just replace the pump for now but since you'll need to remove the oil pan anyway, you might as well replace the bearings while you're there.
ID89GT
10 Year Member
yeah, the oil level is full and clean. I just got done checking the pressure with a mechanic style pressure gauge with a long hose. Once started the gauge went to 50 lbs at about 1200 rpm. Once the engine was warm the pressure settled in at 20 lbs at idle and a quick blip of the throttle brought it up to 45/50. Not sure which is more accurate, but the last test made me feel a lot better.
Some guys here on stangnet seem to think anything with less than 20psi at hot idle is bad, it's really not.
I ran one of my engines down to under 10 at hot idle, lasted that way as a daily driver for a few years. Burned about 2 quarts at that point between oil changes.
Are you burning any oil?
Pumps are rarely ever "weak", most of the time they are either good or bad.
Do not waste your time or energy replacing it.
I ran one of my engines down to under 10 at hot idle, lasted that way as a daily driver for a few years. Burned about 2 quarts at that point between oil changes.
Are you burning any oil?
Pumps are rarely ever "weak", most of the time they are either good or bad.
Do not waste your time or energy replacing it.
HiFlow5 0
Member
As mentioned before, oil pumps on 5.0's are either good or bad, so that would be the last place I would check for weak oil pressure. Factory gauges are also notorious for being highly inaccurate and I'm glad to see you did the tests again with an aftermarket Autometer.
Now the factory spec for an 79-93 5.0L listed directly out of the shop manual states, 40-60 psi hot at 2,000 rpm is normal. I would say that 20 psi at idle is more then respectable as well. What grade oil are you running, you could always bump up to 10w40 as the motor may have been build with slightly looser tolerances, but without actually tearing down the motor and measuring with plasti-gauge you will never know.
-Craig
Chasinpapa
Member
If your gauge is registering that low, try replacing the oil sending unit. If that is what it is, it still may not be as accurate as a mechanical gauge but at least your gauge will be working. $12.00 
http://www.autozone.com/autozone/pa...KeyWord=oil+pressure+switch&fromString=search
http://www.autozone.com/autozone/pa...KeyWord=oil+pressure+switch&fromString=search
The car dosen't burn any oil. I have driven it about a thousand miles since I got the car. As far as oil grade is concerned, I should ask you Craig since this is your old car lol. The autometer gauge is probably not as accurate as the mechanical gauge (I hope). I was only seeing 25lbs when I was on the highway at 2k rpm with the autometer gauge, freaked me out a bit.
HiFlow5 0
Member
In that case it was 10W30, you could always try 10W40 at your next oil change.
And yeah, I would be app to believe the mechanical gauge over anything else. If oil pressure really was low, then you would see signs of it else where. Especially the first time you do an oil change.
25 at 2000rpm is fine.
As long as you are at 10psi per thousand rpm, you are good.
Alot of times here on stangnet i think guys pad their oil pressure numbers, kinda like meatheads in the gym pad their bench press.
That's more like it. Those are good healthy numbers so it seems that both the factory gauge and the Autometer gauge were faulty. Not often that happens. Perhaps the sending units of both gauges were bad.
Sending units in general are inaccurate, best off with a mechanical oil pressure gauge.
Chasinpapa
Member
If that is what it is, it still may not be as accurate as a mechanical gauge but at least your gauge will be working. QUOTE]
Never said it was as accurate as a mechanical gauge, just trying to save the man a little money. He's already shown us with the mechanical gauge that he has sufficient oil pressure.
