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Installing an Oil Pressure Gauge

First, the installation can vary depending on which engine you have, DOHC or SOHC. I'll start with the SOHC, and then name the differences with the DOHC.

Before doing any work, start with a clean work area, with all the proper tools, and plenty of rags.

For this project, you will need (above and beyond normal hand tools):
-YELLOW Teflon tape
-Oil pressure sensor socket (optional, DOHC only)
-3/8" NPT to 1/8" NPT Brass adaptor (optional, DOHC only)
-Assorted electrical connections (bullets, ring terminals, horseshoe terminals)
-Terminal crimper
-3/16" Allen key socket for 3/8" ratchet (optional, DOHC only)

Ok, lets start by discussing a few options that are available.
1.) Keep stock sending unit, and add the aftermarket sending unit
2.) Remove your stock sending unit, and replace with aftermarket sending unit.
3.) Keep stock sending unit, and install sender in the head (DOHC only).
There are a few pros and cons to each for you to consider.

Assuming you have a SOHC, you really only have two choices, add the aftermarket unit, or replace the stock-sending unit with the aftermarket unit. I'd recommend that you remove the stock sending unit completely, and replace with the aftermarket sending unit. Here's why: If you want to keep the stock sender and add the aftermarket oil pressure sender, you need to assemble a "T" fitting, and on each end of the "T" is a sending unit, stock and aftermarket. The problem is that there is not enough room in the back of the block to assemble the "T" and then screw it into the block. You have to assemble the "T" piece by piece, on the engine block. Not fun, and there is a large possibility of leakage, since there is not much room to work back there, meaning it is hard to get all the fittings properly tightened.

Removing the stock sending unit will not cause the oil light to come on, ever.

Now, installation should be pretty easy. Look at the back of the block, between the 3rd and 4th cylinders, and you'll see a bright green plug. This is your oil pressure sender. Remove the plug (it's got a locking tab in it), and with the oil pressure sender socket, remove the stock sender. You may lose about a cup of oil, depending on how long the car has sat. Be prepared for this, no sense in staining your driveway. Here is where you need to make a decision on what you want to do about the sending units. From this point, either assemble a "T" or use the 3/8" to 1/8" NPT adaptor and install the aftermarket sending unit.

BE SURE TO WRAP EVRYTHING IN YELLOW TEFLON TAPE. WHITE TEFLON TAPE CAN BE BROKEND DOWN BY PETROLIUM PRODUCTS, I.E. OIL.

From here, you"ll need to wire up your gauge. Due to differences in how gauges are wired, I'm not going to go into detail on this. Most aftermarket gauges use a one-wire sensor, so that part is easy. The illumination, ground, and ignition wiring is up to you.

If you have a DOHC, you have one more option to the above methods. If you want to install the aftermarket oil pressure sender in the block, follow one of the two methods for the SOHC cars. But, with the DOHC head, there is an oil port in the head, above the 4th cylinder. Look at the back of the head; you will see two plugs, both with Allen key inserts. You want the one farthest from the exhaust manifold, closest to the top of the head. This plug is a 3/16" Allen key. Grab an Allen key socket adaptor from your hardware store of choice, and remove plug. You will not lose any oil out of this plug. Take note, this plug is 1/8" NPT thread. Since almost all aftermarket sending units are 1/8" NPT thread, it just screws right into the head right here. No adaptors needed.

BE SURE TO WRAP EVRYTHING IN YELLOW TEFLON TAPE. WHITE TEFLON TAPE CAN BE BROKEND DOWN BY PETROLIUM PRODUCTS, I.E. OIL.

From here, you'll need to wire up your gauge. Due to differences in how gauges are wired, I'm not going to go into detail on this. Most aftermarket gauges use a one-wire sensor, so that part is easy. The illumination, ground, and ignition wiring is up to you.

It's a good idea to start you car after installing the aftermarket sending unit, to check for leaks. Take it for a short drive, and look for dampness around the sender. If there is not, you're good. Repair any leaks as necessary.

If you have a SOHC, or want to have the sender in the block, my recommendation is to remove the stock sending unit completely. If you have a DOHC, my recommendation is to place the aftermarket sending unit in the head.

You cannot use any aftermarket oil pressure gauge with the stock sending unit. What I mean by this is that you cannot skip installing the aftermarket oil pressure sender and just tap into the stock sending units wiring. It does not work, do not attempt. The stock sending unit is an on-off switch, designed to turn on if oil pressure is less than ~9psi.

Some oil prssure readings from my experiences...
All readings from a '97 DOHC, 10w-30 synthetic oil, "Viper" oil filter.

Sender in the block:
Cold Idle: 50 psi
Cold 3000 RPM: 80 psi
Warm idle: 25 psi
Warm 3000 rpm: 50 psi

Sender in the head:
Cold Idle: 50 psi
Cold 3000 RPM 65 psi
Warm Idle: 10 psi
warm 3000 RPM: 25 psi

Erik Johnson

Ok, update...

It has been brought to my attention that the port on the back of the head on DOHC cars may not all be the same. The physcal location of the ports are the same, but they type of port head is different.

My car, A '97 Plymouth Expresso, DOHC, build date of 10/96 had the ports (like every DOHC), but the plugs were 3/16" allen key size.

Some DOHC's, in the early run ('late '94-'95 sometime), has SQUARE drive inserts for the plugs in the back of the head. I am unaware of the sizing, as soon as I find out, I'll post here.

Also, the late DOHC's ('99ish), have the square plug as well.

The "middle" years of the DOHC have the hex (allen) key insert.

Just a FYI...

Erik Johnson

Ok, more of an update for y'all instaling an oil pressure gauge.

The models with the square head plug in the head (DOHC only, read 1st post), can be removed by using the propler size bit, but also, it can be removed with a little "McGyver" skills.

You can remove the plug by using a small flat head screwdriver/hex ratchet bit. Push the flat head so it contacts two of the diagonal corners, and gently remove. I'd highly reccomend using some penterating oil before remving this plug, regardless what method you choose to remove it with.

The '95ish and '99ish years recieved a square head plug in the head, while the majority of others recieved the hex head...but there are a small number of others that actually have freeze plugs in this location. One particular car I noted it on was a '96 S/C (Dodge; US build). I'm sure there are more, his car cannot be a "fluke," just don't know what years/build location they are.

Once again, the DOHC's are the only heads that have the head oil passage that you can tap into. SOHC's don't.

Erik Johnson

I have some info on this subject.
I have a 97 dohc build date 5-97 with the square plug. The plug is a 3/16 square & you
can do either of the too to help out if you don't feek comfortable using the screwdriver
bit (I know I didn't).
You can get a tool from snap-on. This is called a pipe plug socket, size 3/16. Or you can get some 3/16 square key stock. This is called make-a-key, from a tool supply store.
I thought I would share my experience of finding something to get the job done.
Theressa

Here is mine on a 98 DOHC

Original image no longer available.

Images to replace the missing ones showing the DOHC headports:






Pics borrowed from:
viewtopic.php?f=1&t=330615

Here is the location of the oil sender on the block.

http://www.lon.ca/pics/stockoillocation.jpg

Here it is looking up from underneath. Note the tranny to engine brace in green.

Oil location in red.

http://www.lon.ca/pics/stockoillocation2.jpg

Original mages are no longer available.

on the same note for those who have the square bolts in the head .. you know you can you 3/8 ratchet extrention to take these type of bolts out .. just thought i would put my 2 cents in to it !!!!

You can get a tool from snap-on. This is called a pipe plug socket, size 3/16.


This is a good investment i got one just to put my oil pressure gauge in and worked very very good, I reccomend getting one if u are going to do this install

So, where do we get an aftermarket sensor with 2 wires allready.? Is it something a local auto parts store can get?

I first installed an autometer oil pressure gauge in the block on my 2k3 by just removing to stock sender. From reading this thread and many others I was under the impression that I would have no oil pressure light or codes thrown. Wrong. My oil pressure light came on and stayed on and threw code P0522 code witch means Engine Oil Pressure Sensor/Switch Circuit Low Voltage. I tried grounding the sender wire, the code went away but the light stayed on. I tried splicing the signal wire from the autometer with the stock sender wire; I just got incorrect readings but the light stayed off and no code. So I decided to go with a tee to sole the problem. A few people pm’ed me with questions about the tee so I just made a quick how to.. Hope this helps.

Yeah the oil sending unit is on the block not the head. I think he is talking about adding a oil gauge sending unit. Again all I ever did was remove the idiot light as that's all it really is. I think the light goes on at what 3psi???? Something stupid like that. I just got a fitting and threaded the oil pressure gauge into the oil sending unit threads and called it a day. If you just are replacing the sending unit go to the part store pay the 5 bucks for the socket replace the sending unit and call it a day. Using vice grips or pliars on it you risk breaking the sensor or ruining it enough that you can't get it out with the correct socket. Makes life easier when you work on cars with the correct parts.
Lorenzo