To install an oil pressure gauge first drain the oil and install the sandwich adapter between the engine block and the oil filter. Second, thread the pressure sensor into the adapter using thread sealant (ensuring a proper ground). Third, route the signal wire (or nylon/copper tubing) through the firewall using a rubber grommet. Finally, wire the gauge to a 12V switched power source (ACC), a solid chassis ground, and the dashboard lighting circuit. Below, we expand on the process to ensure a leak-free and accurate installation.

Tools And Materials You Will Need

Oil pressure gauge kit: Electronic or mechanical, see which you prefer.
Oil filter sandwich adapter (also called an “oil cake”): Be sure to confirm the thread specification before buying, such as M20x1.5 or 3/4-16. If this is wrong, it will all be in vain.
New engine oil and a new filter: They have to be removed anyway, so you can perform maintenance at the same time.
Thread sealant: I personally recommend liquid PTFE sealant rather than raw material tape. Especially for single-wire sensors, grounding is very important, and the raw material is more likely to affect conductivity.
Wrench and socket set
Wire stripping pliers and wire crimping pliers
Multimeter: This is a must when looking for a power source.

Step 1: Drain Oil And Install The Sandwich Adapter

The first step is to prepare the engine. Because the adapter is installed in the original position of the machine filter, the whole process is similar to changing the oil.

Release the old oil: Place an oil pan under the car, unscrew the oil drain screw of the oil pan, and let the old oil drain completely.
Remove the old filter: Unscrew the original oil filter element.
The key step: Use a clean cloth to thoroughly wipe the plane of the engine body where it contacts the machine filter. Never leave any residue from the old rubber gasket.
Install the sandwich adapter: Install the O-ring that came with the kit into the groove of the adapter, and then apply a little new oil to lubricate it. Install the adapter seat with the filter interface on the engine body, and then tighten it with the central bolt (extension screw) included in the kit. If you have a torque wrench, it is best to tighten it according to the torque value given by the manufacturer.
A lesson from experience: There are usually several interfaces on the adapter seat. Before you completely tighten the central bolt, turn the adapter seat to the desired angle to ensure that the hole where you will install the sensor is facing a direction that is convenient for operation.
Install a new machine filter: Screw the new oil filter element onto the male thread protruding from the sandwich adapter, and tighten it with normal maintenance force.

Step 2: Thread The Pressure Sensor Into The Adapter

After the adapter is fixed, the next step is to install the pressure sensor (for an electronic gauge) or the compression joint (for a mechanical gauge).

Apply thread sealant: Apply a thin layer of sealant to the NPT threads of the sensor or connector. Again, if you are using a “single-wire” sensor that is grounded by the thread itself, do not use raw material tape. Too many layers of that tape will isolate the sensor from the metal adapter, causing the meter to lose its signal.
Tighten the sensor: Screw the sensor into one of the ports of the adapter. Just tighten it, but do not overtighten. NPT threads are tapered, and if you insist on tightening it too much, you may crack the adapter.
Plug the unused interfaces: If there are extra interfaces on your sandwich adapter (usually reserved for oil temperature sensors and the like), use the screw plug included with the kit and also apply sealant to seal them.

Step 3: Route The Signal Wire Or Tubing Through The Firewall

The sensor is in place in the engine compartment, and now the signal must be transmitted to the instrument in the cab.

Find the rubber grommet on the firewall: Look for the firewall between the engine compartment and the cockpit. Generally, there will be a rubber sealing ring (grommet) that the original car wiring harness passes through.
Protect the line:
Electronic gauge: Pass the signal line from the sensor end through the rubber grommet. My habit is to cover this wire with a layer of bellows, which can protect it from being roasted by the heat of the engine or broken by moving parts.
Mechanical gauge: Pass the nylon or copper tube through. This is extremely important: you must ensure that the tube does not get kinked anywhere, nor does it rub against sharp metal corners. If you think about it, if this pipe is broken, hot oil will be sprayed directly into your cab, with serious consequences.
Seal the entrance: After the wire or pipe enters the cab, check whether the rubber grommet is installed back in place and sealed tightly to prevent exhaust gas or water from leaking in from the engine compartment.

Step 4: Wire The Gauge To Power And Ground

The last step is to connect the wires under the instrument panel. Most aftermarket oil pressure gauges need to be connected to 4 wires:

12V switching power supply (ACC): Connect the “power” line (usually red) to a circuit that is fused and only has power when the key is turned to the “On” or “Accessory” position. Power can usually be taken from the fuse for the radio or cigarette lighter.
Body grounding: Connect the “grounding” wire (usually black) to a clean, unpainted metal body under the instrument panel. A solid ground is critical to the accuracy of the readings.
Instrument light line: Connect the “lighting” line (many are white or orange) to your headlight switch or meter brightness adjustment circuit. This way, when you turn on the headlights, the newly installed instrument can also light up.
Signal line connection: The signal line that you pulled in from the engine compartment is connected to the “Signal” or “Sender” terminal on the back of the instrument. (If it is a mechanical gauge, just screw the compression nut of the oil pipe directly onto the joint behind the instrument).

Final Verification

Before driving on the road, don’t forget to add new oil of the correct grade and capacity. Then, start the engine and check for any leakage around the sandwich adapter and sensor as soon as possible. If the gauge shows a stable oil pressure reading and you have checked that no oil is leaking, congratulations, you are done.

Author: Aiden

“I am an experienced automotive technician specializing in aftermarket upgrades and engine monitoring. With years of hands-on garage experience, I focus on safe, non-invasive modification methods. I wrote this guide to help DIY enthusiasts master the sandwich adapter technique for accurate oil pressure gauge installation.”