mystery oil pressure problem

Start with a good gauge. Mechanical.

Mechanical oil pressure gauge installation..
1.) Remove old pressure sender. It is located down by the oil filter and has 1 wire on a push on screw connector.
2.) Install ¼” pipe tee fitting with a short ¼” nipple on the place where you removed the oil pressure sender.
3.) Install the original oil pressure sender back in one of the tee ports.
4.) Install the gauge line restrictor in the remaining port of the tee.
5.) Connect the flex tubing or hydraulic hose to the gauge restrictor. Be sure to route the tubing or hose away from the exhaust manifolds. Be sure to either use hydraulic hose or oil and heat resistant flex tubing for the pressure line. Do not use copper tubing for the connection to the gauge restrictor or engine. Over a period of time, the vibration will work harden the tubing and cause it to crack and fail.
6.) If the gauge is going to mount under the hood, connect it to the end of the hose or flex tubing. Use some Tie-wraps to secure the gauge and its plumbing to the wiring harness on the driver’s side inner fender.
7.) If the gauge is going to mount in the passenger compartment you get to find a place to run the tubing through the firewall. I suggest that you pick your spot from the inside since that is the area with the most difficult access. Do not run the tubing through the exact same hole as the steering shaft. It will tangle up with the steering shaft and cause major problems.
8.) Install the gauge inside the car in the location of your choosing. Connect the pressure line to the gauge and secure it out of the way of moving parts with Tie-wraps.
9.) Be sure to ground the gauge lighting wire to clean, shiny bare metal. Connect the other wire from the gauge lighting to a light blue/red wire on the radio wiring harness. There are 2 connectors in the radio wiring harness, but only one of them has the light blue/red wire you need for gauge illumination. Solder the gauge lighting wire to the light blue/red wire on the radio harness and cover the soldered joint with heat shrink.

How to solder like a pro - Ford Fuel Injection » How To Solder Like a Pro a must read for any automotive wiring job.

Be sure to use a gauge restrictor fitting in the pressure line going to the gauge. The restrictor will prevent all of the engine's oil supply from ending up on the pavement before you can stop it if the gauge line fails. I had a gauge line rupture, and the restrictor fitting saved my engine from serious damage.

I'm assuming he already has a mechanical gauge because how would he know what pressure he had before?

With that said, the numbers seem to be both ends of the spectrum, hot idle at 40psi is pretty high, below 10 is pretty low.

You burning any oil?

i just bought a 87 lx 5.0 it has a sunpro oil pressure gauge on it. when the car is cold after sitting all night it will have 40 psi of oil pressure as it warms up the pressure will drop to 0 but no noise from the motor and it has been like this for a month going down the road it will run about 18 psi of oil pressure i can't figure it out at all could someone help if they have also had this problem

87stanglx302 said:

i just bought a 87 lx 5.0 it has a sunpro oil pressure gauge on it. when the car is cold after sitting all night it will have 40 psi of oil pressure as it warms up the pressure will drop to 0 but no noise from the motor and it has been like this for a month going down the road it will run about 18 psi of oil pressure i can't figure it out at all could someone help if they have also had this problem

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Sounds like bad bearings from my experience.
If that's the case, get yourself prepared to buy an explorer engine to replace yours.

thats kinda what i was afraid u thinking there is any chance i could rebearing the bottom end and put a new oil pump in and save the motor

87stanglx302 said:

thats kinda what i was afraid u thinking there is any chance i could rebearing the bottom end and put a new oil pump in and save the motor

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It's not worth the trouble.
Explorer engines are $500, sometimes less.

2000xp8 said:

Sounds like bad bearings from my experience.
If that's the case, get yourself prepared to buy an explorer engine to replace yours.

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been there done that. explorer short block with under 100k miles ran me 80 bux. Factor in the cost of a master gasket kit, new head bolts, and intake bolts and I was up and running for about $300 or so.
If the car is a toy run it until it blows. I drove mine for over a year and a half with bad oil pressure. Would drop to zero when I floored it and it would rattle like a bitch while blowing smoke out the tails. It was still running when I pulled it.

Low mileage explorer engine swaps > rebuilding a 302. I can get Explorer/Mountaineer motors for roughly $250 in my area all day long. I actually got a free one once upon a time. Runs like a champ.

I just had a motor that wiped out the bottom end, it had 60 psi pressure I revved it up and it went to about 75 then the oil pump relief valve kicked in and it dropped to around 40...then went down more and more until about 10 psi then zero at idle. There was some crap that went through the oil pump and hung the oil pressure relief valve open so when the engine went back to idle,...no pressure. Just a thought, you can probably jack the engine up and lower the pan to change the pump.

blacksheep-1 said:

you can probably jack the engine up and lower the pan to change the pump.

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That plan almost never works.
In my time as a 5.0 owner (almost 20 years now) with a friend that owns a shop specializing in mustangs, i've not ever seen or known anyone that changed just the pump and had it make a difference.
It's a risky plan that is a serious PITA. Pulling the pump with the engine in the car is not for a novice, in fact it's easier for most people to pull the engine.

I pulled the pan with the engine in the car this last summer and that was just to replace a leaky gasket. I will never do it again. far easier to drop pull the engine.

Bad bearings often manifest as oil pressure that drops as RPM increases and often leave silver in the oil pan. Pulling the pan probably isn't a bad idea at this point anyway...

stykthyn said:

I pulled the pan with the engine in the car this last summer and that was just to replace a leaky gasket. I will never do it again. far easier to drop pull the engine.

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Yup, it's a lesson you only need to learn once.

I'd love to know how the hell a socket gets in the oil pan.

sounds like someone was trying to spin the driveshaft with it and dropped it down the hole and left it rather than try to drop the pan.