Low oil pressure?

thaduke2003 · Sep 25, 2007

Yep- you guessed it- I have low oil pressure. Tried swapping on a new pressure switch to see if maybe it was just that, but no dice. Changed the oil with a new filter- no luck there. I even put a new breather cap on the driver's side- still nothing. So...
Any ideas?
Any chance it's the pump? If so, is it possible to swap the pump with the engine in the car?
By the way, no signs of leaks, or lifter noise. No oil in the coolant (that I can see), and no other ideas! Thanks- Mark W.

BK_CAULEY · Sep 25, 2007

just to be on the safe side have a mechanic shop test your pressure with a differebt gauge. you might have a bad gauge. but if its good your pump is prolly clogged

thaduke2003 · Sep 25, 2007

What's normal pressure for a 5.0 pump? Thanks- Mark W.

rocknrod · Sep 25, 2007

what kind of mustang

I have an 91 lx 5.0 and took motor mounts loose and changed the oil pan gasket and went ahead and replaced the oil pump. my oil presurre is 60 lbs when cold and about 45lbs hot

ninety15.0 · Sep 25, 2007

You should see at least 10-15 psi when at HOT idle. This is the condition in which you will be testing it. I think the minimum ford spec is something ridiculously low like 5-8psi at hot idle. I would like to see at least 15-20 depending on the weight of the oil and the ambient temps. Good luck

praugue · Sep 25, 2007

My 1989 also reads low. However, it's been like this for 4 years, so it should have blown up by now.

I did remove the power from the sensor (near the oil filter) and cleaned up both contacts. It seems to be reading a bit higher now. My 1992 reads about 20 to 45. The 1989 now reads about 15 to 35. I guess it's okay.

Both of them run quiet, smooth, and strong. If there wasn't a gauge, I would never suspect a problem existed, so ...

facemelter71 · Sep 25, 2007

I just did a oil pump 3 weeks ago on my 89.Remove the power steering rack,two bolts,and the steering nuckle bolt and let the rack hang there.Remove the oil pan bolts and lower pan unto the k-member.Remove the two bolts to the pickup tube that face the passenger side and then remove the two bolts that hold the pump to the block.Now you should be able to have plenty of room to work in there without removing the pan or jacking the engine up.Replace the worn out pump with a mellings high volume pump and go buy a ARP heavy duty oil pump shaft.Then reinstall all the good stuff and your good to go.

praugue · Sep 25, 2007

Further info:

The gauge reads from 0 (red mark) and increases by 20PSI per marking.
So the gauge will read (from top to bottom, as it's a vertical gauge):

100
80
60
40
20
0

My 1989 reads between 20 and 40 most of the time. My 1992 reads a bit higher, 20 to 50 or so. Neither of them have ever read 60.

60 would have the needle horizontal, so mine always read a bit less than horizontal. When they get down to 20, the look of the low reading is unnerving.

65ShelbyClone · Sep 25, 2007

Half the problem is trying to guesstimate pressure based on the stock gage. When I had my '89 GT the gage said ~20-30 psi at idle and 30psi at ~3500rpm. It was actually 50psi on the Autometer at 3500.

Get an accurate gage before worrying about the reading.

bloopbloob · Sep 26, 2007

praugue said:
Further info:

The gauge reads from 0 (red mark) and increases by 20PSI per marking.
So the gauge will read (from top to bottom, as it's a vertical gauge):

100
80
60
40
20
0

My 1989 reads between 20 and 40 most of the time. My 1992 reads a bit higher, 20 to 50 or so. Neither of them have ever read 60.

60 would have the needle horizontal, so mine always read a bit less than horizontal. When they get down to 20, the look of the low reading is unnerving.

mine always reads higher than horizontal, even at idle. It sits between the R and O on the word NORMAL. I'm guessing thats 60-80! Bad Gauge? Its a newer pump though.

corvetteguy · Sep 26, 2007

My 89 GT gauge also reads low
and always has.
It hovers around the oil lamp symbol.

I blame it on the stock gauge. But before I would
worry I would buy a $10 mechanical gauge
and install it.

ninety15.0 · Sep 26, 2007

I also had the same problems. And when i built the current motor and assembled everything again...i had what appeared to be even lower oil pressure than i did with the old engine. It was always below horizontal...and when it was at HOT idle..it was very low...scary low. So i threw a autometer mech oil press gauge on there and when i first started it up and saw the pressure immediately build to 65psi i was relieved....it settled down to a hot idle of 25ish. Once i touch the throttle it jumps up to about 35-40...and it sits a 50 for hot cruise! Good luck man

praugue · Sep 26, 2007

Odd that such an "iffy" gauge would be provided. Any suggestions on a decent replacement?

thaduke2003 · Sep 26, 2007

OK- hooked up an AM gauge- we're good- I'm within spec everywhere- the stock gauge just sucks.
Next question- what's the name of the piece below the water temp sensor? Where the hose to the WP goes in? That sucker's leaking coolant and killing my temp. gauge readings- thanks! Mark W.

65ShelbyClone · Sep 26, 2007

praugue said:
Odd that such an "iffy" gauge would be provided. Any suggestions on a decent replacement?

It's not odd at all; most cars have gages like that. The ones that don't have dummy lights instead. Autometer, VDO, and Stewart Warner are some good replacements.

thaduke2003 · Sep 27, 2007

Yeah- as a tech, I've seen a lot of cars WAY out of spec, but the temp or oil pressure gauge says nothing until it's at the "Oh #$#@!" point of about to pop. Recently saw a Cherokee (lucky she had the bulletproof 4.0L) that went 100 miles (NYC to our area) with a hole in the bottom of the rad you could fit a pack of smokes through, and the light only went on when the car had hit over 240 degrees! At that point, she still only popped a head gasket- amazing motor! But yeah, time for a rebuild anyway...
The idea behind that is to keep customers from heading for the service bay every time their water temp goes up 2 degrees over what they might think to be "normal," a damper is put in to keep the gauge from oscillating. Some are extreme, turning the gauges into on/off warning lights, some (Audi used to be VERY accurate- not sure about newer ones) actually function as you would think they should. Cheers Mark W.

65ShelbyClone · Sep 27, 2007

Maybe, but remember that no gage is going to register hot when the cooling system is dry.

remat457 · Sep 27, 2007

corvetteguy said:
My 89 GT gauge also reads low
and always has.
It hovers around the oil lamp symbol.

I blame it on the stock gauge. But before I would
worry I would buy a $10 mechanical gauge
and install it.

Interesting, my 89 does the same thing.

SuperStang83 · Sep 27, 2007

I had lost all oil pressure on my stock gauge, so I put in an Autometer. I was extremely lucky and it was just my stock gauge becasue the autometer one read fine. As a rule of thumb you are supposed to have 20 psi at idle and 10 psi for every 1k RPMs after that.

Low oil pressure?

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