Oil Pressure Fluctuates

[90' LX 5.0]

My oil pressure guage is acting up. While driving on the freeway, it is on the low side of normal...

When I come to a stop, right before i come to a complete stop, the car shifts(its an auto) and the oil pressure drops to absolutely nothing. sometimes it comes right back up, but once in a while it kinda twitches and stays down.

When i start moving it comes back up again.

Is this something to worry about?

 

[NKau]

It most certainly IS something to worry about. How many miles are on the engine? First thing I'd do is pick up a cheap mechanical autogage oil psi guage and put it in to get a semi-accurate (the factory guages won't tell you squat) reading on where the oil pressure is. You want to note what the psi is on cold startup, warm idle, and warm cruise. You want at least 10 psi at warm idle, and 25 psi at warm cruise. Typically a healthy 5.0 seems to make about 25 psi at warm idle and 40+ psi at warm cruise. The standard is 10 psi of oil pressure for every 1,000 rpm your engine is turning.
You may have an oil pump issue, but if mileage is high, I'm guessing you are just due for a rebuild.

 

[04sleeper]

The easiest thing to do is try a new sending unit. They are like $10 and see if that is the culprit.
A mechanical gauge would be better but more expensive.

 

[90' LX 5.0]

there are 140,000 miles on the car.

Just last week i had a new oil pump installed, new crank, new main bearings, new rod bearings.... I probably shouldve stated that before.

Car runs great.

 

[NKau]

If that's the case, I'd be apt to just try '89sleeper's advice. If that doesn't change things, I'd still see if I could get my hands on a really cheap mechanical guage just to verify that there isn't a serious problem.

 

[gregpro50]

there are 140,000 miles on the car.

Just last week i had a new oil pump installed, new crank, new main bearings, new rod bearings.... I probably shouldve stated that before.

Car runs great.

Ummmm..... I'd be very worried then. Get a mechanical guage just to make sure but it sounds like a problem with the crank/bearings. Who did the work ??

 

[04sleeper]

If that's the case, I'd be apt to just try '89sleeper's advice. If that doesn't change things, I'd still see if I could get my hands on a really cheap mechanical guage just to verify that there isn't a serious problem.

Agreed!

Also check the tube the oil pressure gauge screws into. If there is anything obstructing it or the sending unit it will not read right.

 

[90' LX 5.0]

Ummmm..... I'd be very worried then. Get a mechanical guage just to make sure but it sounds like a problem with the crank/bearings. Who did the work ??

The work was done at a Ford Specialist.

not a dealer.

 

[gregpro50]

I had the same thing replaced by a mechanic on a car I owned and there was too much play between the crank and the bearings causing very low pressure at idle.

 

[90' LX 5.0]

I had the same thing replaced by a mechanic on a car I owned and there was too much play between the crank and the bearings causing very low pressure at idle.

Ok... But the oil pressure isnt always low at idle. Sometimes its in the middle of the normal range. Ive also discoverd that if the oil pressure guage is reading no pressure, and i put the car into park, the pressure comes back.


So if its the Oil Pressure sending unit. Would this just effect the guage reading? or the actual pressure itself?

And where exactly is the sending unit? Im kinda a noob with the whole 5.0...

 

[9T3SVT]

Oil pressure sending unit is located at the front of the block, drivers side. It's big and it sticks out right behind the power steering pump. There is also a wire on the very top of it. It takes a deeeep socket to get to it, they sell the special socket at most parts stores. Or you can cut off the tip and use the regular deep socket.

 

[ECU5.0]

DONT RELY ON THE STOCK GAUGE!....i dont know how many people have said this before for other gauges like water temp...but do not rely on the stock gauge. if all else fails just get a cheapo temporary gauge to hook up so you can see what the oil pressure is and than hook the stock gauge back up. after i installed an aftermarket water temp gauge.....i wont trust the stock gauges for anything

 

[1988WHTGT]

I had the same problem. Well kind of....Mine would drop to zero whenever I got on it right after I did a rebuild on it. So I just took off the wire going to the sending unit, cleaned it up and put it back on tight and all was good.

 

[Js5ohLX]

Mine did the same thing exactly, my main bearings were junk and the crank smoked. I'd get a mechanical guage (twelve bucks for a cheap one) and see what you really have. I'll guess you have a problem though.