Oil Pressure Gauge Acting Funny

[Ralleytuned]

When driving on the freeway, I have noticed the oil pressure gauge drops when I hit a speed of about 70mph. I don't think it has done this before, it seems to have just developed. I started with the obvious, checked the oil, topped it up to full and drove it again. The problem still persists.

The truck is an 83 3 speed auto, I believe it has a 2.3 from what the PO said

When i'm on the freeway cruising around 65, the gauge reads right in the middle. If I accelerate to about 72, the oil pressure gauge slowly drops to the lowest part of the "normal" range. Mind you this is only about 100 rpm higher than at 65 (ish). If I slow back down to around 60, it will go back to the middle.

Here is the weird part, when driving around town, If i accelerate to a much higher rpm, or put it in "2" and drive up high in the rpm, the oil pressure gauge doesn't move. Also, on the hwy, at 60-65, when I climb a hill, the pressure gauge drops also. It honestly seems to correlate with throttle position more than RPM.

So that is where my issue is with trusting the gauge, it doesnt correlate with RPM, it seems more with throttle position, which doesn't make much sense to me haha Any thoughts?

I have a sneaking suspicion the only way to know is to put a mechanical oil pressure gauge on and drive to see if the gauge is accurate or just simply having electrical issues.

 

[tomw]

As they say, "It all depends..."

Do you have an oil pressure sending unit with a 'dome' or is it the black plastic & metal screw-in switch?
The 'dome' or cylinder type actually measure pressure, and send a variable voltage to the gauge. The needle on the gauge moves in response to the voltage signal.

The black plastic switch type are a on/off switch, and provide ground to the cluster to move the gauge needle. There is a resistor attached to the cluster that will put the needle in the middle of its range. If pressure falls below 5-6 psi, the switch will open, and the needle will fall to the low reading area.
In the former case, a dropping reading may have significance actually relating to the pressure. I would try connecting a mechanical gauge at least temporarily if you are concerned.
In the latter case, I'd suspect there's a voltage variance occurring, making the gauge read different. I'd suggest connecting a voltmeter to monitor changes.
Actually, now that I think more, I would suggest monitoring voltage as both setups are electrical in their operation, and the regulator on the cluster may not be regulating exactly.
tom

 

[RonD]

+1 ^^^

Not sure if 1983 used "real" sender or a switch sender, late '80's were all switches, ON/OFF.

If oil pressure needle goes up from idle RPMs to 2,500RPMs matching RPMs then it would be a "real" pressure sender.
If it just goes up to 1/4-1/2 on startup and stays there then it is a switch sender most likely.

And the dropping needle at higher RPMs is usually a sender issue not an oil pressure issue, UNLESS you also hear valve train noise.

But senders of either type are not expensive, and usually not to hard to change, so I would change that first.

2.3l sender was drivers side, rear, under intake but on the head

Senders use 1 wire, that means the threads on the sender are the Ground for the circuit, you MUST leave some bare metal threads so sender can have a good ground with engine.
So if you use sealing tape leave end threads bare.