18
Nov
2019

Triple Gauge Swap, part 2

As I mentioned before in part 1, my want for these gauges started after installing my oil cooler, and second-guessing my ability. Obviously the Defi gauges have their associated probes/sensors. Instead of the individual gauges, these probes all plug into the back of the Defi control unit. The oil temperature and water temperature gauges use what seem to be identical thermistor probes (I did an experiment to test both consistency and accuracy of the probes, which I will post later).

When mounting these sensors you have a few choices for easy installation. on the engine block (technically it’s the upper oil pan) there are existing OEM probes for oil temperature and pressure. Using these existing locations is the lowest hanging fruit for getting the probes mounted. I wanted to retain both the existing sensors (oil temperature, and the oil pressure switch (it’s not a sensor, but an on/off switch to trigger a CEL). From memory, this switch comes on at 7psi, which is much too late to save your butt if you lose your oil. Retaining the oil pressure switch will prevent any warning lights from a missing sensor. Retaining the OEM oil temperature sensor is required for me to get this data on the CAN bus (for a later project that I have in mind). The below image shows the disconnected oil pressure switch and oil temperature sensor. The oil pressure switch is on the left, with the black connector. For reference, these sensors point toward the front of the engine, and to the left of the oil pressure sensor is the mounting stud for the oil filter.
OEM oil pressure and temperature probes

Given those requirements, this is how I chose to install my sensors:

Oil Pressure
As I said, I wanted to retain the OEM oil pressure switch while adding the Defi oil pressure sensor. I decided to buy a tee fitting and mount the two sensors to that. Because oil pressure will basically be the same throughout the entire tee fitting, there is no problem with these sensors not being in the active oil stream. Here is a shot of the OEM and Defi oil pressure sensors. I don’t like to use thread tape on these parts, so I used some plumber’s pipe dope. It’s non-hardening and rated in liquid applications to temperatures and pressures that I will never see in a vehicle. You can see this if you look carefully at the tee fitting.

OEM and Defil oil pressure sensors

It’s technically a tee fitting AND an extension, which I needed for the OEM oil pressure sensor to clear for mounting. I wasn’t worried about the length of the extension, even though the perspective on some of the pics makes it look like it’s a mile long. My main concern was the weight of the OEM oil pressure switch causing the arm of the extension to clock around and come unscrewed. I checked many times after driving around, and it never budged.

OEM oil pressure switch Tee
OEM oil pressure switch Tee

Oil Temperature
The oil temperature probe took just a little more thought to mount. With the pressure switch/sensor, it didn’t have to be placed in a circulating channel; pressure is pressure anywhere in the tee. This is not the same with the temperature probe; for an accurate reading, it really should be in the stream of circulating oil. If I were to use a tee fitting there would be a lot of non-circulating oil around the probes, which isn’t going to cut it. When I got the OEM probe out of the block, my final decision was made for me; the OEM probe and the Defi probe are different sizes. The Defi probes are 1/8 NPT, but the OEM is not. Z1 motorsports sells the exact same tee fitting that I bought for $2, but they want over $15 for it. They advertise that it can be used for the OEM oil temperature probe, but it clearly can not. I approached them about this, but their only answer was that the OEM was 1/8 NPT, even though I showed them a picture of the probes side-by-side. I will give Z1 the benefit of the doubt; it’s very possible that Nissan used different sensors for different years. Just be warned that model year 2017 vehicles use oil temperature probes that are NOT 1/8 NPT! Do these threads look the same to you? Someone on the forums mentioned that it looks like the temperature probe from the GTR, which I can neither confirm nor deny. All I know is that it’s NOT 1/8 NPT, regardless of what Z1 says. The left is the OEM probe and the right is the Defi. In the background you can see the tee fitting, which does NOT fit.
OEM and Defi oil temperature probes

My solution for this was a Greddy oil pan drain bolt that is tapped to receive the 1/8 NPT probe for the Defi sensor. It worked out perfectly. The bottom of the sump may not be the exact most optimal place to measure the temperature of the oil, but once it came up to temperature there was only 5-7 degrees difference between the two locations (remember, I still have the oil temperature data on the CAN bus by keeping the OEM probe 😉 )
Oil temperature probe with pipe dope
Oil temperature probe with pipe dope
Greddy oil pan drain bolt with temperature probe
Greddy oil pan drain bolt with temperature probe

Water Temperature
TBD

Oil Cooler
Just a few quick pictures of my oil cooler and oil cooler block off plate (It cools too well in the Michigan winters). The pics of the radiator are looking up from underneath the car while it’s on a lift. The Z1 logo sticker is good for at least 5 rwhp.
Oil cooler
Oil cooler block off plate
Oil cooler block off plate

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2 Responses

  1. Ken says:

    You would likely find this useful, if you haven’t stumbled upon it already. https://projectbytes.wordpress.com/2013/08/25/nissan-370z-can-hacking/

    • don says:

      His blog (which I found from some threads in the 370z forums) is what really got me interested in playing around with the CAN bus on the Z. I planned to mention/link to him when I add a post specifically about playing around on the bus. Thanks!

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