modifications > 2025 Transfer Case Cooler Duct
Why did I install a 2025 Transfer Case Cooler Duct?
The GR Corolla is currently one of the best hot hatchbacks on the market. However, one of the issues with the GRC is transfer case heat management. My GRC is a daily driver, so I have never witnessed the dreaded "AWD System Overheated Switching to 2WD Mode" warning message.
Toyota released a revised undertray beneath the engine for 2025 models. Instead of purchasing the entire undertray for ~$250, I opted for the $40 revised panel insert only. This panel insert has a NACA duct that feeds cold air towards the transfer case. With a little bit of ingenuity, I added
(3) strakes to guide air over OE cooling fins on the bottom of the transfer case.
Date Completed:
12/18/25
Materials:
- 2025 Undertray panel insert #51405-12070 (Price Leblanc Toyota)
- KYDEX Sheet, 0.080" thick, black, 8x12", 2 pack (Amazon.com)
- Scrap cardboard
- Gorilla Epoxy
- P80 sandpaper
- Sharpie
Tools:
- 1/4" drive ratchet, 6" extension and socket (10mm)
- Dremel with cut-off disc
- Flat-blade screwdriver
- Measuring Tape
- Metal Shears
- Scissors
- File
Notes:
1. No wiring plugs need to be temporarily disconnected for this modification.
2. When you glue the KYDEX pieces to the rear scoop, make sure not to get any epoxy on the removable panel. Oil changes would be difficult later.
3. I recommend a respirator if you trim the KYDEX with a Dremel. The dust cloud is pretty harsh to human lungs.
4. Although this Gorilla Epoxy specifically states it isn't recommended for polypropylene plastic, it worked just fine.
5. Work fast with the Epoxy. It sets pretty damn quick. Mix small puddles to spread.
6. Reversible back to stock, but it might leave a little mess.
Removal:
1. Remove OE undertray. (x4 10mm, eleventy billion push clips)
2. Remove OE undertray panel insert. (x4 10mm)
Installation:
1. Install 2025 undertray panel insert into OE undertray.
2. Make cardboard templates for strakes to guide air from panel insert NACA duct to OE transfer case fins.
3. Transfer cardboard templates onto KYDEX sheet.
4. Cut strakes out of KYDEX sheet.
5. Sand the rear duct on OE undertray for Epoxy to have a better bond.
6. Glue strakes to rear duct on OE undertray.
7. I let the Epoxy cure for at least 18 hours before reinstalling the OE undertray.
8. Trim strakes as needed to clear OE oil pan.
9. Reinstall OE undertray.
10. Reinstall undertray panel insert.
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