TH400 Transmission Cooler, new and ready to install. Fits the TH400. Ships fast from the USA.
If your TH400 truck, motorhome or big-block street car smells hot after a long pull, slips on the highway once it is heat-soaked, or keeps cooking fluid behind a loose stall converter, the radiator tank cooler is usually not keeping up. This kit adds a dedicated auxiliary cooler and the plumbing to run it: a Derale tube-and-fin cooler measuring 17.5 x 7-5/8 x 3/4 in. with its mounting kit, rated for vehicles up to 20,000 lb GVW, two 6 ft lengths of -6AN braided steel hose, two 90-degree and two straight -6AN hose ends, -6AN transmission adapters in both 1/4 in. and 1/8 in. pipe sizes, and cushioned line clamps to hold the run in place.
In the Turbo 400 the front pump feeds the pressure regulator, the regulator charges the torque converter, and the oil leaving the converter, the hottest oil in the unit, is what goes out to the cooler. GM's service section shows the return coming back through the pump cover, where it lubricates the gear train, bushings and thrust washers before draining to the pan. So the cooler does two jobs: it pulls heat out, and its return flow is the lube supply. A tube-and-fin core makes the oil take several passes through the core before it leaves, which gives it more time to shed heat than a single straight pass. Mounted ahead of the radiator in clean air, it takes load off the radiator tank cooler or replaces it on a swap that never had one.
Check the fluid hot in Park; a level that is low or overfull causes foaming and heat on its own. If the fluid is dark, drop the pan and read the debris before blaming the cooler; a unit already shedding lining needs a rebuild, and the new cooler protects the next one. Our TH400 common problems guide walks through what overheating does inside the unit. Then look at the existing lines for kinks, crushed sections and rusted clips; a restricted line starves lube flow even with a big cooler on the end of it. The TH400 cooler line replacement guide covers GM's flow check.
The kit is sold for the GM TH400, TH350 and 700R4, so it suits a 1964-1990 TH400 truck, motorhome chassis or car, and most hot rods running one of the three. It is a universal auxiliary cooler, not a bolt-in factory part: you choose the mounting spot and cut the hose to length. Check the threads in your case before plumbing it. GM's TH400 torque table lists the cooler connector as 1/4-18 pipe thread, but cases and aftermarket fittings vary, and some ports are straight thread. If you are unsure which unit you have, the TH350 vs TH400 identification guide helps, or send us the year and VIN. More parts for this unit are on our TH400 parts page.
A firmer shift also cuts heat by shortening slip time; the TH400 shift kit is the usual companion on a tow rig. If the pan shows the unit is already worn, reseal it with the TH400 overhaul gasket and seal kit while the cooler goes in.
| Fits | TH400 |
| Part type | Transmission Cooler |
| Condition | New |
| Brand | GM |
| Reference | TH350 |
| Ships | From the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Yes. It is an auxiliary cooler kit sold for the GM TH400, TH350 and 700R4, with -6AN hose and transmission adapters in 1/4 in. and 1/8 in. pipe sizes. You pick the mounting location and cut the hose to length. Check whether your case port is tapered or straight thread before installing the adapters.
A Derale tube-and-fin cooler, 17.5 x 7-5/8 x 3/4 in., with mounting kit; two 6 ft sections of -6AN braided steel hose; two 90-degree and two straight -6AN fittings; two -6AN x 1/8 in. and two -6AN x 1/4 in. transmission fittings; and cushioned line clamps.
The cooler is rated for vehicles up to 20,000 lb GVW, which covers most TH400 pickups, 3/4 and 1-ton trucks and many motorhome chassis. Mount it in clean airflow so it can actually use that capacity.
On most trucks, yes. Run the fluid through the radiator tank cooler first and then through this one so the oil comes back cooler. If the radiator cooler is contaminated from a failure and cannot be flushed clean, bypass it and run the auxiliary cooler alone.
The TH400 takes Dexron-type ATF. Add enough to fill the new hose and cooler, run the engine, then set the level hot in Park after cycling through the ranges.
