PSA: The Data Tells the Truth - Why My Air-to-Water Oil Cooler Made My GR86 Run HOTTER
An Analysis of 1.2M Lines of AiM Solo 2 DL Telemetry
A Cautionary Tale and Lesson Learned for Me
As a scientist, I rely on data to make critical decisions, and I apply that same rigorous methodology to track car prep. Recently, I was asked by a fellow forum goer how my GReddy Air-to-Water Cooled Oil Cooler performed, so I pulled the AiM telemetry data from my '23 GR86 (mostly stock: fluid, brake pad, BBK, wheel (8”), and camber bolt upgrades + cooler)—over 1.2 million data points across 7 track days at Buttonwillow, Willow Springs, and Chuckwalla—to evaluate my cooling setup.
See Our Other Blog Posts:
- Let's Get You to the Track! Getting Started with HPDE Events
- HPDE First-Timer Checklist
- Driving Techniques to Review for Your First Track Day and Beyond!
- The Complete HPDE Track and Resource Guide: Best Resources, Racetracks, and Organizers (2025)
- Track Day Packing List
- Mental Exercises for Motorsport Racing: Sharpening Your Competitive Edge
- Basics of HPDE Racing Data Analyses: Unlocking Speed and Skill
- Modifying Your Car for HPDE: A Deep Dive for Performance Enthusiasts
- Essential Books for High Performance Drivers Education Days
Check out these must read books!
1. Objective & Methodology
This analysis evaluates 1.2 million rows of AiM Solo 2 DL telemetry data collected across 7 distinct track days (Buttonwillow, Willow Springs, and Chuckwalla) in a 2023 Toyota GR86. The primary goal was to mathematically isolate the performance of the GReddy Air-to-Water Cooled Oil Cooler Kit and determine if it provided effective cooling.
2. General Data Summary & T-Test Analysis
The raw data revealed a counterintuitive result: installing the front-mounted GReddy auxiliary air-to-water oil cooler resulted in higher maximum oil temperatures than running the car entirely stock on days with high ambient temps. A Welch's T-Test confirms this variance is statistically significant (p < 0.001).
(Oil: Motul 300V 5W-30, ½ qt overfill)
| Configuration | Track Sessions | Avg Oil Temp (°F) | Max Oil Temp (°F) | Max ECT (°F) |
|---|---|---|---|---|
| Without Cooler | 732,660 data points | 235.27°F | 260.6°F | 210.2°F |
| With Cooler | 512,840 data points | 236.44°F | 271.4°F | 212.0°F |
Oil temps with (blue) and without (orange) the air-to-water cooled oil cooler
3. Track Weather & Engine Thermodynamics
To understand why this cooling system failed, a Multiple Linear Regression model (R²=0.495, n=100,000) was applied to control for RPM, Speed, and Track Time. The model proved that Engine Coolant Temperature (ECT) dictated Oil Temperature at a nearly perfect 1-to-1 ratio (Coefficient: 1.0342, p < 0.001).
Regression Model Snapshot (Dependent Variable: OilTemp)
| Variable | Coefficient (Impact on Temp) |
P-Value | Statistical Significance |
|---|---|---|---|
| Cooler Presence | -0.6138°F | <0.0001 | Significant (but mechanically negligible) |
| ECT (Engine Coolant Temp) | +1.0342°F | <0.0001 | Highly Significant |
| RPM | +0.0022°F | <0.0001 | Highly Significant |
Impact of other factors on oil temps
The table below highlights exactly when the cooling system hit a thermal runaway. On a 98.6°F day at Buttonwillow (not uncommon during the track season), the ECT crossed the 210°F threshold. At this temperature, the coolant became a "warm blanket," losing its ability to absorb heat from the oil, triggering a spike in oil temp to 271.4°F.
| Track Name | Date | IAT (Ambient) Min-Max | Avg ECT | Max ECT | Max Oil Temp |
|---|---|---|---|---|---|
| Willow Springs | Sept 2024 | 55.4°F - 107.6°F | 185.9°F | 204.8°F | 260.6°F |
| Chuckwalla | Nov 2024 | 56.3°F - 84.2°F | 175.3°F | 210.2°F | 249.8°F |
| Buttonwillow | Sept 2025 | 65.3°F - 98.6°F | 185.7°F | 212.0°F | 271.4°F |
Impact of RPM and ECT on Oil Temps with (yellow) and without (blue) air-to-water oil cooler
My Biases: How did I end up here in the first place? Well, this is my third 86 platform, and I have run both the Jackson and GReddy air-to-oil coolers over the last decade. I have had two failures, one catastrophic. Both were likely install and/or maintenance errors, but it has made me gun shy about adding a failure point to the oil circuit again, despite my very trusted advisors warning me this is absolutely needed for my use case.
My Potential Solution: I am thinking of pulling the GReddy front-mounted air-to-water cooler out and switching to the Ansix Auto Top-Mount Air-to-Water Oil Cooler. Why?
- Thermal Efficiency: It mounts in the engine bay, completely unblocking the front grille so the main radiator can “breathe 100% fresh”, ambient air.
-
Oil Pressure: Ansix and the track community state they have evaluated that replacing the restrictive OEM heat exchanger drastically improves baseline oil pressure (saving us from the purportedly 20-30psi pressure drops seen in other dual-radiator kits, which is more likely a fairly benign 5psi drop).
- I have oil pressure data too, more on that another time. Suffice it to say, with a stock 86 you are likely fine, at least my car is, even without an oil cooler in regard to oil pressures (though one would certainly help).
- Safety: Zero long oil lines running to the front bumper. Easily accessible for inspection and maintenance.
4. Solutions, Claims vs. Data Reality
A. GReddy Water-Cooled Upgrade Kit
* Manufacturer Claim: GReddy explicitly states that their air-to -water kit is "engineered specifically for street use but has been rigorously tested on the track to confirm its performance." However, they concede: "When running continuous laps or drifting, please install the air-cooled [air-to-oil] GReddy Oil Cooler Kit..."
* Data Reality: While the air-to-water oil cooler installed cools the fluid inside it, mounting it directly in front of the car's main radiator caused severe Airflow Stacking in this use case. It blasted 150°F+ "dirty" exhaust air into the main radiator, suffocating the primary cooling system.
* Review Consensus: Track enthusiasts across GR86.org and Reddit consistently echo this limitation. As one veteran track builder on r/GR86 noted regarding dual-radiator/water-cooled setups: "If you're not tracking, this is a perfect solution... [but] I do not recommend this for track day type driving."
B. Ansix Auto Water-to-Oil Cooler Kit
* Manufacturer Claim: Ansix states their top-mounted kit will "stabilize oil temperatures with the coolant temp and consistently operate around 212ºF." Critically, they note: "The stock heat exchanger on the FA24 has been measured to cause a substantial pressure drop. Our kit is designed to be used without the stock heat exchanger to allow your engine to have higher oil pressure."
* Testing & Data Projection: In Ansix’s own track testing (30 minutes continuous on a 59°F day (not a lot of time and low ambient temp), oil never exceeded 226°F. Because the Ansix kit mounts on top of the engine block, it completely unblocks the front bumper, allowing the main radiator to “breathe” 100% fresh ambient air.
* Review Consensus: The track community highly regards the Ansix approach for solving the stock FA24 heat exchanger pressure drop issue, though the drop is minor (approx 3-5 PSI). One reviewer on r/GR86 confirmed the Ansix efficiency: "2 of our local guys ran Ansix and saw a 10C drop in water temp on consistent hot track days. It's very much recommended."
The Takeaways:
If you run a front-mounted water/coolant sub-radiator on this platform, you are choking your main radiator with hot air. Unblock your grille, optimize your oil pressure.
If you track in 100-degree SoCal (or other location) heat, consider an air-to-oil cooler and/or upgrading your main radiator, (the later especially if you choose a air-to-water oil cooler). I am by no means stating a water-to-oil cooler is superior, just my current preference based on individual experience. One need look no further than the Toyota GR86 Cup car builds (900BRZ Cup Car Reliability and The Autopian GR86 Race Car).
Limitations: One car (two drivers), data compared over a year’s time, single geographic location. Number of observations inflates significance calculations. Data may not be generalizable and will vary based on build and use case!
5. Next Steps for me
- Remove the GReddy front-mount kit to restore clean, ambient airflow to the main engine radiator.
- Install the Ansix Auto Water-to-Oil kit to restore maximum oil pressure and cut the risk of front-mounted oil line leaks (my own neuroses).
- Monitor ECT Closely. If tracking in 95°F+ California weather and ECT crosses 215°F, upgrade to a thicker all-aluminum main radiator (e.g., Koyorad or CSF) or go back to the air-to-oil oil cooler everyone recommends.
- Manage Radiator Airflow (Optional/Non-Destructive): To support the stock radiator handling the Ansix's heat without cutting holes in the hood for aero vents, I will consider using high-density foam to seal the airflow gaps around the front bumper, or ultimately bolting on an aftermarket pre-vented track hood (like Seibon/Sayber, since I don't want to cut into my hood) to evacuate high-pressure hot air and increase front-end downforce.
We hope you found this helpful! We wish you fun and safe tracking!