Aftermarket gauges

The tach signal should be the easy part.
That is usually done with an inductive pickup on one of the plug wires.
Might be a bit trickier with a "coil on plug" arrangement though.

Almost all of the signals are passed around digitally on a CAN bus arrangement and will be hard to tap into.

Hope someone else has experience and can help out.
This might end up being a LOT harder than you imagined.

 

I use a ScanGauge II for all those items (and quite a few more), except for oil temp. Works great.

 

With an XGauge I believe it will do oil temp. Haven't tried that myself. Mines actually a mess at the moment, and it was giving me problems: likely too much weight on the obd port, was causing false alarms. Anyway, here's a list of xgauges (add-ons you can program into ScanGuage). Getting the hang of adding XGauges is a slow and painful process, easily forgotten too.

GEN III XGAUGE master list | CleanMPG

 

Oil temperature or even oil pressure can be had with adapters that fit the currently plugged M18x1.5 threaded machining access channels in the oil filter adapter. Adapters can be had to attach an oil pressure tube to the gauge or an oil temperature sensor.

 

While ScanGauge is digital display only, Torq and various other OBDII-port tools and apps can select analog gauges too.

Use a Bluetooth dongle on the OBDII port, a spare Bluetooth-enabled smartphone as the display, and an app on the phone. That gets lots and lots of user selectable gauges, with analog choices too -- except for the oil temperature.

 

There's been a lot of talk in other threads about the fact that zero miles to empty really means at least 50 miles and the amount of fuel in the tank when the bar gauge says none.

These OBDII scan gauges all have "fuel level" data. With these, is there still a "safety" factor or does zero mean as close as it can figure to zero?

 

The fuel level (FLV) displayed on my ScanGauge-II continues falling for a while after my last fuel bar starts blinking and DTE reaches zero. But then it hits a floor value (0.7 gallon on my SG-II) and ceases falling even though the tank is still not empty. It can't get down to zero. I use this as an additional gauging point below anything that the dashboard will show. I think DTE=0 corresponds to about 1.4 gallon on my display, but it was been a while since I ran that low so could be misremembering.

This floor number is probably dependent on car parameters that one initially enters when setting up the SG-II. It takes only whole gallon fuel tank capacities. I think I entered 11 gallons, so others who enter 12 may see a different floor figure.

Note also that the SG-II fuel display is unfiltered, so exhibits a lot of slosh that doesn't appear on the dashboard display. The FLV display will slosh up from its floor, but not down. So when it is stuck at the floor and showing no slosh peaks anymore, it is getting really low.

 

If you've ever siphoned off fermenting wine or beer jugs, you go very delicately when almost down to the dregs. The bottom of the gas tank is likely much cleaner, but still, it's best to avoid the slosh zone.

The flip-side to that argument: maybe you want to regularly give it a good swirl, homogenize things, so you don't get a big slug of sediment the one time you run it down. Who knows.

 

This is really great info and EXACTLY what I was looking to find out. My summary of the DTE thread seems to indicate that DTE=0 corresponds to 1.8 gallons in the tank, but 1.4 is in the ball park.

I'm trying to grow a pair and get used to the idea that when DTE=0, there's at least 1.5 gallons left, I always get at least 35 MPG, so I can go 50 miles without getting my knickers in a twist.

 

Note that the 0.7 and 1.4 numbers I mention are not accurate gallons-remaining figures, they are just numbers on an artificial scale. And the zero of this artificial scale is not set at the true zero of the tank. Think of it as analogous to the Fahrenheit and Celcius temperature scales, their zero points are not set at real Abosolute Zero, negative numbers on F and C are possible. But in this case, I just don't know what the true bottom of the fuel tank would read, only that the fuel sensor stops before it gets down there.

But at least the OBDII monitors can read farther down than does the dashboard gauge.

The 1.8 gallons you are thinking of is probably closer to reality. Do be sure to read the base post of this thread:
[WARNING] Running out of gas (Gen III) | PriusChat

If you do this -- and nothing says that you must do so -- at least be sure to test it in circumstances where failure doesn't cascade into additional problems. I.e. the first test to new depths of the tank should never be in foul weather, or in remote places where spare fuel or assistance is sparse or unavailable, or in heavy high speed traffic, or at a time when a half day's delay would cause you to miss anything important.

Those are not the right times to discover that you have misfigured the remaining fuel. Schedule your "discovery" for a time and place that minimizes the inconvenience caused by that "discovery".

At least in the old days when fuel filters were replaced frequently, I did want to swirl it up occasionally to trap a little bit at a time when it didn't matter much, to help prevent a big slug at a critical time. Today, filters are replaced much less often.

As for siphoning that beer and wine, that would be analogous to fuel tanks only if the hose was always held at a fixed point at (near) the bottom, even when the jug is full. I.e. always sucking at dregs level.