New Gauges for Mazda3

[MeteorGray]

I love vehicle instruments, so when China spread the results of its bat virus research on the world in 2019 and cut my driving to virtually nil, I spent some of the resulting idle time by installing a couple of instruments on my 2015 Mazda3.

Specifically, I installed engine oil pressure and oil temperature gauges, since Mazda did not see fit to install sensors on those values for OBDII reporting. I have long followed many other engine operating readings via the Mazda's OBDII and a ScanGauge, but these engine oil values are not accessible without additional gauges.

For the engine oil temperature, I installed an electric Autometer oil temperature gauge. It showed me no surprises: it takes three or four times the miles to fully warm up the engine oil compared to what it takes for the engine coolant. Such a gauge teaches the driver to keep off the heavy throttle for a while after a cold start if, that is, he/she/it cares about such things as longer engine life.

For the engine oil pressure, I installed an electric Stewart-Warner oil pressure gauge. In contrast to the oil temperature gauge, it did show some surprises. Namely, that modern cars like the Mazda use the engine computer to control oil pressures in order to glean extra fuel mileage. To wit:

When starting the cold Mazda 2.0L four-cylinder engine, the oil pressure immediately jumps to 20PSI and stays there. This is in stark contrast to my older vehicles. For example, my 2003 4.0L six-cylinder Jeep Wrangler jumps to about 80PSI when cold-started, as does my 1996 7.3L Ford V8 diesel.

Why the difference in oil pressure? Mostly because it has been found that engines don't need the high oil pressures found on older engine designs. And since it takes energy to force the oil pumps to achieve such elevated pressure values, the older engine designs are using more fuel than necessary.

This extra fuel usage didn't make as much difference back in their day, but in today's world it is a no-no to modern fleet makers in view of ever-tightening EPA fuel economy requirements and penalties for noncompliance of such.

This oil pressure differential between old and modern engines continues on the highway. Whereas my older vehicles show maybe 50PSI at highway speeds even when fully warmed up, my Mazda3 shows the same 20PSI that it did at cold idle!

Indeed, I have found that up to 70MPH on flat highways, the Mazda's oil pressure stays at 20PSI. Only when I hit 80MPH did the oil pressure go up to 30PSI.

Presumably, had I dared risk life and limb and ticket and continued to exceed the speed limit to ever-higher violation levels, the oil pressure would have continued its upward climb in order to protect the engine from the growing stress and strain and RPMs.

In the same vein, when the Mazda is forced to accelerate hard to quickly gain speed or when going up steep hills and bridges to gain altitude, the growing engine stress requires additional engine oil pressure for protection to its groaning rod journals and bearings and etc, and so the engine computer commands oil pressures as high as 70PSI or so to meet the need. Obviously, the computer knows that saving the engine is more important than a few ounces of fuel when high loads are present.

When I got back into town after the highway test run, the slow traffic and hot engine oil cause the oil pressure to drop, down to about 10PSI or so at idle and slow engine speed. This oil pressure level is not a surprise with the 0W20 synthetic oil used in many modern cars to meet EPA fuel efficiency requirements, and the load on the engine when going slow in the city does not require high oil pressures anyway. Of course, it rises when the engine load increases.

Traditionalists might cringe at such low oil pressures observed on an oil pressure gauge on modern cars, but as Dylan's song declares, The Times They Are A'Changing.

Only with an oil pressure gauge could I observe the results of the engine's computer controlling the engine oil pressure. On my Mazda, the oil pressure is controlled by opening and closing an oil pressure control valve as needed. On some other modern cars, the oil pressure is controlled by manipulating a variable-pressure oil pump. Either design works to the same effect.

Some manufacturers claim a 3% to 6% increase in fuel economy from such oil pressure control. This seems a bit high to me, but obviously there are some worthwhile fuel savings, or they surely wouldn't bother with all that computer and mechanical attention to the details.

In any case, I do love vehicle instruments, and my engine oil gauges are the latest iterations to satisfy that passion.

[freebeard]

In my 1961 VW Type II, I had installed oil temp and pressure gauges; but also a head temperature gauge with two sending units on a toggle switch. I could compare #1` and #3.

[Daschicken]

Cool to hear, i've got a 2014 mazda3, so it probably does the same things.

[MeteorGray]

Yeah Daschicken, your 2014 Mazda3 has the same engine design as my 2015. In fact, Mazdas have been using the Skyactiv SA-G engine design since 2012. It has proven to be a very efficient and reliable powerplant.

[Ecky]

Very interesting read, thank you. Do you have any idea how the control valve works? That is, is it a partial bypass of oil back through the pump? Or more like a restrictor?

[MeteorGray]

Ecky, I don't really know.

I can say that the engine oil pressure is managed by the computer using an "engine oil solenoid valve."

So, when the computer sees oil pressure that is higher than needed, it opens the oil solenoid valve to bleed off some pressurized oil to the oil pan and reduces the pressure; and when the oil pressure is lower than needed, it closes the oil solenoid valve and sends it through the engine and increases the pressure.

However it works, it works!