I would like to share some info on the G16E-GTS oil system for anyone curious or unsure if it needs upgrading. This isn’t a complete guide or anything, just a few data points from 3 GRY (well, more like 2.5) and some thoughts on the matter.
Here’s how the oil pressure vs. RPM looks during regular city driving. The car is a stock 2023 (with an oil pressure/temperature sensor in the oil housing) GR Yaris running Toyota 0W-20 SP ILSAC GF-6 oil. The x axis shows RPM, and the Y - oil pressure in kPa. Colors represent oil temperature, with the legend on the right. You can see how the maximum oil pressure decreases as the oil temperature rises. This is likely because hotter, thinner oil can bleed through a smaller relief valve opening, reaching equilibrium at a lower pressure.
View attachment 31468
The next one shows a scatter plot from early GRY (pre 07/2021, with the oil temp/pressure sensor in the engine block—so slightly lower pressure readings) runs on the track. The car had stock engine power, Nankang AR-1 265 tires, an engine oil cooler (leading to even lower sensor pressure readings), no oil overfill, and no significant weight reduction. And the plot looks quite different.
The dot colors represent oil temperatures ranging from 85°C to 125°C. A 40°C increase in oil temperature leads to a pressure drop from around 350 kPa to 270 kPa. The temperature/pressure "slices" are still clearly visible, but there are more scattered dots of different colors at the lower end, indicating oil pressure drops at varying oil temperatures.
If you look closely at the top of the graph, you’ll notice that the oil pressure drops closely follows the longitudinal acceleration "drops" (braking events). Every longer braking event at ~1G results in a pressure drop of about 150-130 kPa. Interestingly, these drops don’t seem to get worse with increasing oil temperature. On the other hand, lateral acceleration barely affects pressure at all. There are some small ripples in the oil pressure (not clearly visible in the picture due to scale) during ~1.1G corners, but they’re insignificant compared to the impact of longitudinal Gs.
View attachment 31469
In this picture, the dot color represents throttle pedal position. This seems to confirm what I mentioned earlier. As you can see, almost all pressure drops happen off-throttle. The few traces showing on-throttle events (the ones not in blue) are due to the pressure still recovering after the brake pedal was released and throttle applied.
On this GRY oil relief valve seems to open, and oil pressure plateaus quite early at ~2700 rpm, compared to the first picture, where at the same temperature, oil pressure levels off at ~3100 rpm. I’m still trying to figure this out. Could it be caused by the added restriction from the oil cooler, a different relief valve spring, or something else?
View attachment 31470
Different Yaris (pre 07/2021), AR-1 255 tires, engine oil cooler, no overfill, slight power increase (~20hp), and no weight reduction. The oil temperature range in the graph is 90°C to 135°C, with a pressure drop due to the temperature increase going from 380 kPa to 280 kPa. There are even bigger pressure drops under braking, with deltas reaching up to 190 kPa.
Just like in the previous example, higher oil temperatures don’t lead to a greater pressure drop. It might look like the scatter plot is crowded with orange dots in the pressure drop areas, but that’s simply because the sample count in the orange range is the highest.
View attachment 31471
View attachment 31472
What conclusions can we draw from all this?
First, under heavy braking, oil sloshes in the sump significantly, and this isn't affected by oil temperature so isn't affected by viscosity as well. Thicker oil wouldn’t help with that, but baffle plates, an improved sump, or an accusump should. I’ve tried gathering data from cars with baffle plates installed but haven’t had any luck so far. If anyone has logs they’re willing to share, that would be really helpful.
Second, you definitely need a big oil cooler if you plan to track the car, but that’s old news.
It’s also well known that GRY’s oil pressure under load is relatively low. What can we do to improve it?
Thicker oil? Maybe, but I’m unsure how that would impact LSPI prevention.
Using a stiffer relief valve spring or shimming the existing one?
Oil coolers with shorter rows and a higher row count reduce pressure less, but there isn’t much space in the GRY to fit such a cooler.
Shorter cooler pipes, smoother elbows, and a bigger oil filter could improve pressure slightly.
Ditching the standard oil heat exchanger and routing pipes to the cooler from there, using an external oil thermostat instead of a sandwich plate, could help as well.
Curious to hear your comments and insights.
