Need a new oil pressure gauge

[Skunksmash]

My old oil pressure gauge is finally going kaput. I've got two new sending units on the engine, so I doubt its that. The gauge has always been kind of flaky, but now its acting like its knocking on death's door. My oil pressure really isn't something I want to leave to chance, so I've decided to replace the gauge with a good aftermarket one. So:

1. What size are the oil pressure gauges in these old trucks? is it 2.5"? I ask because sometimes accepted standards aren't the actual measurements.

2. Given the 3 wire (or was it 2..) nature of the oil pressure gauge, am I looking for a "mechanical" oil pressure gauge, or electrical? Not too sure on that one.

3. What numbers should I have on my gauge? You can get a lot of different types of gauge faces with various numbers depending on your application. My engine is a 350 TBI. What should be my lowest, medium, and highest numbers on the oil pressure gauge?

[Skunksmash]

Bump

[PAWS 72]

Like to know also. The 87 I bought about 3 months ago the gauge isnt working in it either. It has pressure and it stays at 30 psi all the time.It doesnt move.I placed an order for some more parts so I ordered a new gauge. Hope that's what it is.

I have replaced the sending units so I know thats not the problem.

[chengny]

These gauge don't usually fail.

If they aren't reading correctly (unresponsive, erratic or pegged in either direction) the problem is almost always related to the associated wiring.

The operating principle is fairly simple:

Variable voltage type gauge theory of operation - just as general information:

VARIABLE VOLTAGE TYPE
The variable voltage type dash gauge consists of two magnetic coils to which battery voltage is applied. The coils act on the gauge pointer and pull in opposite directions. One coil is grounded directly to the chassis, while the other coil is grounded through a variable resistor within the sending unit. Resistance through the sending unit determines current flow through its coil, and therefore pointer position.
When resistance is high in the sending unit, less current is allowed to flow through its coil, causing the gauge pointer to move toward the directly grounded coil. When resistance in the sending unit decreases, more current is allowed to pass through its coil, increasing the magnetic field. The gauge pointer is then attracted toward the coil which is grounded through the sending unit.
A special tester is required to diagnose this type gauge. Follow instructions included with the tester.

Gauge failures are often caused by defective wiring or grounds. The first step in locating trouble should be a thorough inspection of all wiring, terminals and printed circuits. If wiring is secured by clamps, check to see whether the insulation has been severed, thereby grounding the wire. In the case of a fuel gauge installation, rust may cause failure by corrosion at the ground connection of the tank unit.

Basic schematic. Note: this is applicable to all dash indicators (i.e. gas tank level, coolant temp, oil pressure):




Here is a half-assed diagram I made to try to demonstrate how the gauge actually reacts to the two resistances (variable through the sensor and straight to ground):





It shows a coolant temp sender/gauge but the oil pressure indication is the same.

If your oil pressure gauge is sporadically jumping up to the pegged high end - it would indicate a short to ground in the sensing lead that goes to the 0-60 sender. I think it's a tan wire.

No reaction - the oil pressure gauge always reads 30# while the other gauges are fully functional - would indicate a broken (but ungrounded) lead to the sensor.

[Skunksmash]

Same here replaced both sending units. One was leaking, and when I replaced the other, the gauge did work well for about 2 months. But now its doing the same thing yours is. And as we all know they're supposed to move on a chevy. I sent autometer an email and he said it would be an electrical gauge, and that you gotta replace the sending unit with the one that they supply. He said that their sending unit is going to be more accurate than the factory one.


He also said the pro comp should match the factory gauges pretty well, since its a black face with yellow numbers and tickmarks. I hope its not the sending unit down by the oil filter, cause that one was a pain.

[chengny]

My old oil pressure gauge is finally going kaput. I've got two new sending units on the engine, so I doubt its that. The gauge has always been kind of flaky, but now its acting like its knocking on death's door.

Not sure what your set up is but, C/K trucks with gauges have two oil pressure sensing devices. Like this:






One of them is a switch (closes when oil pressure reaches 10#). That is the one with 2 male spade terminals. It supplies power to the choke heater when engine oil pressure is established. On truck without gauges it also controls the oil pressure warning light on the dash (idiot light). NOTE: On trucks with gauges it will light up the "choke" light when oil pressure is below 10 psi. If the engine is running and the "choke" light comes on - shut down. It should be considered as a low oil pressure warning.


The other is unit (the one shaped like a bell & with only one terminal) is a sender. It provides a variable resistance to ground for the sensing leg of the oil pressure gauge. As oil pressure fluctuates (between 0- 60 psi) the sender reacts accordingly.

So anyway, check your sender. If it is original it may be getting sticky inside. It is just a diaphram that acts on a wire wound resistor through a crank arm. They get old and don't react well - new ones are on the shelf at any auto parts store (maybe $10).

Here is an image of the guts:

[Skunksmash]

Thanks everyone for all the helpful info. But at this point, I'm really more concerned with the specifications of the gauge itself. The autometer rep wasn't sure of the exact size of gauge I should order for the truck, in order to recess it into the factory spot. Does anyone have that information on hand? I want to rule out the old flakey gauge as a culprit, and it would be nice to have a more accurate, better looking new one in there anyway. In my experience, these factory gauges aren't the best.

Some people around here are proud of them but eh, gauges get old just like everything else and the water temp gauge, and fuel level gauges that I've bought are far superior to the factory ones that they replaced. I have doubts that the oil pressure gauge would be any different. So I'm not really looking for alternatives or other fixes. Just the info I originally requested.

[chengny]

1. What size are the oil pressure gauges in these old trucks? is it 2.5"? I ask because sometimes accepted standards aren't the actual measurements?

I'll let you figure out what size these gauges are:







2. Given the 3 wire (or was it 2..) nature of the oil pressure gauge, am I looking for a "mechanical" oil pressure gauge, or electrical? Not too sure on that one.

You are actually looking for an "indicator". This is a remote reading device that is not actually in contact with the pressure being monitored. The sender basically converts the actual oil pressure to a resistance - and that resistance is used to move the needle on the face of the indicator. This type of indicator is considered to be an electrical instrument. A gauge would have a length of tubing with one end connected to the back and the other end connected to the oil system.

3. What numbers should I have on my gauge? You can get a lot of different types of gauge faces with various numbers depending on your application. My engine is a 350 TBI. What should be my lowest, medium, and highest numbers on the oil pressure gauge?

The stock sender is calibrated to make the indicator read from 0 - 60 psi. Unless you plan on installing a sender I would spec your new gauge to read from 0 -60 psi as well.

[dieseldawg142]

Originally Posted by Skunksmash

Thanks everyone for all the helpful info. But at this point, I'm really more concerned with the specifications of the gauge itself. The autometer rep wasn't sure of the exact size of gauge I should order for the truck, in order to recess it into the factory spot. Does anyone have that information on hand? I want to rule out the old flakey gauge as a culprit, and it would be nice to have a more accurate, better looking new one in there anyway. In my experience, these factory gauges aren't the best.

Some people around here are proud of them but eh, gauges get old just like everything else and the water temp gauge, and fuel level gauges that I've bought are far superior to the factory ones that they replaced. I have doubts that the oil pressure gauge would be any different. So I'm not really looking for alternatives or other fixes. Just the info I originally requested.

are you replacing the small gauge? i did my small gauges with auto-meter sport-comps. used 2 1/16" gauges. with just 1 stock gauge working, it sure is nice now knowing whats going on under the hood

[INSIDIOUS '86]

Check my signature. I went with sun pros myself
Posted via Mobile Device

[Skunksmash]

Originally Posted by INSIDIOUS '86

Check my signature. I went with sun pros myself
Posted via Mobile Device

In the sig link you said:

Originally Posted by INSIDIOUS '86

So I have my iroc gauges that I built a long time ago. I just pulled them out today to do a overhaul on the dash..

I assume you were taking the gauges out of the Camaro and putting them in the truck? I'm afraid I am unfamiliar with the way that gen Camaro's gauges looked. Also, I looked through the thread, but I didn't see what size gauges you used for the smaller gauges. I'm concerned about having the numbers and marks either too squished together, or too far outside the edges so that you can't see all of them well. So of course getting the right size gauge for the hole in these old trucks is important.

I ask because I'll be using SunPro as well, on this oil pressure gauge swap.

[Skunksmash]

Gotta bring this thread back to life.

The type of oil pressure gauge I want to buy is short sweep electric, right? Just want to be clear. The gas gauge had me a little confused.

[Skunksmash]

Bump