What we recommend
An in-radiator trans cooler works, but behind an LS3 and 4L70E we recommend running it in series with a separate external cooler. Radiator-integrated coolers are the cleaner install and what most factory Chevy setups use; an Entropy LSX-specific radiator even has a built-in 2-row trans cooler. The case for a separate fan-cooled cooler is that it keeps converter heat out of the engine radiator, which matters in heavy traffic or staging lanes, and a good medium unit costs under $200 (DeRale units with coated fins, multi-row multi-pass construction and AN fittings are a solid choice). What we've seen work well is plumbing through the radiator first and then an external cooler; one such setup runs around 150°F trans temps and adds fluid capacity. The 4L70E is borderline behind the 480 hp / 495 lb-ft LS3, so err toward more cooling.
Check this first:
- Confirm your radiator has an internal trans cooler and its fitting size
- Find a mounting spot for an external cooler with airflow
- Decide whether the external cooler fan runs on its own switch
Careful: The 4L70E is borderline behind 480 hp / 495 lb-ft, and letting it run hot will shorten its life.
Check this first
- Measure trans temp under load; sustained over 200F needs more cooler
Try this, then this
- External cooler in series after radiator — Derale routing. Worked if: temps under 200F
- Bigger cooler + fan — more capacity. Worked if: temps under 200F
How you know it's fixed
- Trans temps stay under 200F towing/driving hard
Still not fixed?
- Add larger cooler with fan; consider trans upgrade
Key numbers
| What | Value |
|---|
| 4L70E capacity | rated ~495 lb-ft; marginal at 480 hp |
Every option we know of
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| Maker / product | Part # | Fits | Price | Where | Status / notes |
|---|
Derale
stacked-plate cooler | 13503 | universal | about $80 | Buy
Summit | In production |
B&M
SuperCooler | 70264 | universal | about $90 | Summit | In production |
Tru-Cool
40k cooler | LPD47391 | universal | about $120 | Buy
parts store | In production
large — check mounting room |
Prices are approximate as of September 2026. We list every option we know of, including small shops and used parts we can't link to. Confirm fitment with the seller.
Time and cost: 2-3 hours
