Oil Pressure
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Joined: Sep 2006
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From: Oh
Oil Pressure
Howdy folks, i just wanted to know some of yalls input.So if you can help me out it would be highly appreciated. Well my oil pressure likes to jump around, at idle it will sit at 30 sometimes lower then as soon as i give it some gas and drive it will sit around the 50 mark..and i think its triggering my add coolant light,because it will go off, but as soon as i rev its will shut off. i dont think its is my coolant because the car is always at appropriate temp(1/8 to 1/4 above the C) and im always checking my coolant and its always above full and i always check for a air bubbles in the system, because that was the cause of the last engines death. so if anyone can send some knowledge maybe about why the oil temp is jumping around.
P.s- it is a used engine at 60k and seems stong.
P.s- it is a used engine at 60k and seems stong.
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Joined: Dec 2005
Posts: 34
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From: Indiana
The oil pressure is largely dependent on the RPM. Mine runs 60-65 driving down the road and 35-40 at an idle. If it jumps around at a constant RPM, check the connection at the oil pressure sending unit. I had some corrosion on that terminal once that caused the pressure to fluctuate and the connector doesn't fit very tight sometimes.
Originally Posted by bradenscreed
how accurate is the stock oil pressure gauge? is it worth getting an aftermarket oil press. gauge?
Originally Posted by My5ABaby
The stock one sucks. Get an aftermarket if you want to see what the numbers really are.
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Joined: Dec 2003
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From: Temple, Texas (Central)
Originally Posted by Aaron Cake
Apparently the OEM sender is just a two pressure switch. One position for low pressure, one for high pressure. So the gauge really only has two readings...
The Extremist
Joined: Jun 2006
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From: Bridgewater, Nova Scotia
Originally Posted by Aaron Cake
Apparently the OEM sender is just a two pressure switch. One position for low pressure, one for high pressure. So the gauge really only has two readings...
EDIT: Ugh. after reading whats below, I guess I am pretty much forced to take back what i said. I dont know.
Last edited by mikaz; Nov 17, 2006 at 12:57 PM.
Originally Posted by jazzmanbob
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.
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.
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