Finally added oil temp and boost gauge

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I've had an Arduino embedded computer with an LCD screen that previously was just used for monitoring my ATF temps plus a few odds and ends. Just added an oil temperature sensor and a boost/vacuum sensor.

Attaching a sensor to the side or bottom of the pan can give inaccurate readings especially here because the pan has thick walls (reinforces block and bolts to transmission) and oil near the walls and bottom is largely stagnant. I'm also not yet brave enough to drill and tap into a pressurized oil gallery. Even if I wanted to tap there, I'd have to go through the ordeal that is dropping the pan just to have sufficient room, and I'd be worried I'd mess up and be out $400 for a new pan.

Instead I attached a thermistor to the outside of the oil passage between the pump and the oil thermostat as shown. This solves the problems with stagnant oil and thick walls because the oil is fast and turbulent after turning the 90 degree corner, plus the passage walls are thinner aluminum. I used Arctic Silver thermal adhesive, a thermally conductive epoxy normally meant for electronics, but the datasheet claims it handles temps in excess of 150C / 302F, so it seems up to the task.



Here's a quick shot after about 7 minutes idling while testing the cooling system for leaks after replacing the coolant thermostat. Ambient temp was 16C / 61 F. Interesting how fast the oil warms up at first (40C / 104F after just 3 minutes), but the temp rise slowed down after this, and was at 74C / 165F when I shut off the engine at around 10 minutes.

ATF takes a long time to heat up, since it's just getting pumped around without doing any work here.

Vacuum seems pretty healthy as well, starting at around 18 inHg and rising to 22 or so as things heat up and expand into the correct shape.




Next up is adding a datalogger so I can have fancy graphs to look at. Wish I had done this before winter so I could watch that freezing cold oil slowly come to life.
 
That is super cool. Did you write the software yourself, or use base code like MPGuino or similar? What's the max temp that you've seen on the gauge?
 
Originally Posted By: Jonzobot
That is super cool. Did you write the software yourself, or use base code like MPGuino or similar? What's the max temp that you've seen on the gauge?


Wrote it all myself, though I've had to learn as I go so some is taken from "known good" example code for certain functions.

Max ATF temp was 115C / 240F climbing a grade in the southwest. I quickly dowshifted to let the torque converter lock up and the temp fell back to a more sane 100C / 212F. I've since added an external transmission cooler, so hopefully I won't overheat it again.

Still working bugs out of the oil temp sensor and data logging, and seeing if I can measure the coolant temp as well so I have those data points to plot alongside oil and ATF temp.

Also want to add an oil pressure sender, but that is a whole can of worms with taking the intake manifold off and rigging up some NPT to metric adapters.
 
For oil pressure, I think the most common way to go is to tee off where the oil pressure switch goes into the block. That's what I did, anyway (just a plain mechanical gauge). For you it may be worth it to source an electronic pressure sender from a junkyard somewhere and plug the wires into the Arduino. Then it's just a matter of figuring out the voltage/resistance map - hopefully it's in the relevant car's manual.
 
Sourcing a sender unit and the programming to make sense of it is the easy part.

Just getting to the factory oil pressure switch involves taking the whole intake off, which is doable but still very time consuming. I'm pretty sure the switch is M14 x 1.5 thread pitch, but don't know for certain. If I get it wrong, I either have to waste many hours putting the car back together then taking apart again, or have it sit out of commission until I can get the correct parts.

I'd need an adapter from the block's thread pitch to 1/8 NPT or whatever the electronic sender uses. Getting the factory oil pressure switch hooked back up to that setup might be annoying. Probably a 1/8 NPT tee that I have to drill out and tap to take the M14 x 1.5, and then I have this whole contraption hanging off the side of the block.

Instead I may use the Arduino to switch on the low oil pressure light according to the electronic sender. I could then have the opportunity to make a "smart" oil pressure warning that looks at RPM as well and yells at me if the pressure drops below spec for that engine speed. That would give early warning while cruising, as the idiot light illuminating at highway speeds means the engine is already dead.
 
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