In my 88 SE, N/A, the oil pressure recently and suddenly dropped about 10 psi at idle and 20 at 3000+. It had been fine before that, 30psi at idle, 60psi at rev. It looks like the OMP might be leaking as there is a wet spot underneath. As far as I could see it looks like one of the tubes is cracked or broken. I was wondering if something like that could cause that kind of pressure drop.
Thanks

 

Not in a million billion years. They could all fall off at the same time and it won't effect the oil pressure.

Buy a cheap aftermarket SunPro oil pressure MECHANICAL gauge from you favorite store and find out what the REAL oil pressure is. That's what the FSM suggests.

 

i second the mechanical part. i've had two autometer oil pressure sending units go out on me on two different cars.

 

so if one of your OMP lines broke off and you had oil spewing out it wouldn't effect your oil pressure? So what is usually the most common sympton that causes low oil pressure?

 

I believe theres a thing that controls it with a spring pushing it outward, you can leghten the spring to pull it out more, thus more pressuer as I read

 

Maybe, but he said a bit of oil was leaking under the OMP. That explains pretty much every 7 on the road.

 

Well obviously if all your oil was being blown out a split cooler line you wouldn not have any pressure...

The most common cause of low oil pressure in these cars is a defective oil pressure gauge.

The 2nd most common cause is a blown front cover o-ring.

 

i have seen numerous front cover o-ring failures, first test the pressure with a mechanical gauge then i would suspect the timing cover o-ring to have gone on a vacation. also be sure to replace the broken OMP line.

 

Thermal Pellet anyone?????

 

I was trying to figure out why the resistance reading on the oil pressure sending unit did not change with the pressure. FSM symbol for the sending unit is a variable resistor. So using my compressor I did some tests. Guess what? 42.8 ohms regardless of pressure over 25 psi or thereabouts. Using air, oil water makes no difference to the gauge. The fluid simply exerts pressure against a diaphragm that moves a lever inside the sending unit.

So curious as I am, I dissassembled the oil pressure sending unit. It basically is a pressure switch. At lower than a certain pressure a resistor is in line with the sender feed voltage. this causes the gauge to show a nominal value. When the pressure reaches a certain level there are contacts that connect and allow the gauge to ground out and read a higher level. That is why the reading does not change with the pressure change.

The position at which the switch makes contact is adjustable once the oil pressure sending unit is dissassembled.

Since the gauge in the dash has a thermal actuator to move the needle (heating wire around a bi-metallic strip) when the motor slows or speeds up switching the voltage to the dash gauge on and off, the needle position changes very slowly as the thermal actuator needs time to warm up and cool down.

So the impression is that you are actually seeing a reading of the changing oil pressure with the changing RPM but that is not the case.

This has been a puzzle for several weeks for me as I have been trying to establish accurately what my oil pressure is. I installed a Smiths mechanical gauge from my old CooperS and found I had 75 psi at 3000 rpm and around 48psi at 1200 rpm. I was actually able to read about 5-6 psi on cranking rpm with this gauge. With the sending unit it was all or nothing.

I am trying to keep my car as original as possible but I would like to know precisely what my oil pressure really is. So I will install a Brass T fitting into the oil pressure sending unit hole, mount the OEM sender in one branch of the T so my factory gauge continues to "function" as intended and install my mechanical Smith gauge in the other branch so I really know what is going on.

 

Heh, that's funny. I always thought it was an actual pressure sensor...

 

Alright, i'm going to put a different sending unit on from the old engine that did work, and I will be replacing the omp lines ASAP. I'm glad i've got a spare car.