66RFE Transmission Cooler, new and ready to install. Fits the 66RFE. Ships fast from the USA.
A 66RFE truck that tows well when the weather is mild but overheats the transmission on a hot day, or one where the cooler stays cold while the fluid temperature keeps rising, may not have a bad cooler at all. The problem can sit one step upstream, in the thermostatic bypass that decides whether fluid goes to the cooler. Be clear on what you are buying: this page is titled transmission cooler, but the part is a new RevMax thermostatic bypass upgrade, manufacturer part number 68RFE-929AA. Its manufacturer lists it for the 2013-2018 68RFE and Aisin AS69 and states it also fits the 66RFE. It bolts into the cooler circuit in place of the factory bypass and keeps your existing cooler.
The 66RFE belongs to the same Chrysler RFE family as the 68RFE, and on the 2013-2018 heavy-duty Rams covered here the cooler circuit is managed by a thermostatic bypass. Cold fluid is steered around the cooler so the transmission reaches operating temperature quickly, and the valve should open to send hot fluid through the cooler. According to RevMax, the factory valve can hang up in its cold position, leaving the transmission with no cooling at all, and even a healthy factory unit carries an internal orifice that RevMax says cuts cooler flow by 87 percent. The upgrade replaces that module with a billet 6061 aluminum, finned, USA-made body with no thermostat and no orifice, so every drop of return fluid passes through the cooler.
Start with the cheap checks. Read fluid temperature with a scan tool on a loaded drive, then carefully feel or measure the cooler inlet and return lines; a hot inlet with a cool core points at a closed bypass. Next run a flow check: the ATRA trade journal GEARS Magazine calls for at least a gallon per minute out of the return line, measured with a flow meter or into a bucket. GEARS also reminds technicians that 200 degrees F is the ideal ceiling and that life is halved for every 20 degrees above it. If flow is fine, check load against your tow rating, engine cooling and the fan clutch. The RFE family shares many failure patterns, so our Ram 2500 RFE common problems guide and RFE shift solenoid symptoms guide are useful when heat has already caused shift complaints.
This listing covers 2013-2018 trucks built with the 66RFE. RevMax builds separate bypass parts for 2010-2012 and for 2019 and newer trucks, and those do not swap with this one, so the model year matters. Confirm your transmission on the build sheet or the tag on the case, and confirm that your truck still has the factory bypass module in the cooler lines. If you are unsure, send us the year and VIN and we will check before it ships. You can see our full range for this transmission on the 66RFE collection page, and the closely related 68RFE collection lists parts shared across the family.
No cutting is required: the manufacturer says the existing lines unplug from the factory bypass and plug into the new module. Have a drain pan ready, keep dirt out of the open fittings, and replace any seal that looks flattened or cracked. Refill with ATF+4 and set the level hot, at 160 degrees F or above, per the FCA procedure for this family. Expect a slower warm-up in winter since cold fluid now goes through the cooler too. If the fluid is burnt, service it before trusting the truck to tow again. A unit that is already slipping needs more than better cooling; a worn pump can be addressed with our 66RFE pump, and a high-mileage unit is a candidate for the 66RFE overhaul kit.
| Fits | 66RFE |
| Part type | Transmission Cooler |
| Condition | New |
| Brand | OEM |
| Ships | From the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. It is a thermostatic bypass upgrade that replaces the factory bypass module in the cooler lines. Your existing cooler stays on the truck.
The manufacturer lists it for 2013-2018 trucks and states it fits the 66RFE as well as the 68RFE and AS69. Different parts are used on 2010-2012 and 2019-up trucks, so send us your year and VIN if you are unsure.
Check cooler flow at the return line, which should be at least a gallon per minute, then look at towing load, engine cooling and the fan clutch. A plugged filter or restricted line can also cause heat.
ATF+4. Set the level with the fluid at 160 degrees F or higher after the install.
Not directly. It only changes cooling. Keeping the fluid cooler helps protect clutches and solenoids, but a transmission that is already slipping will need repair.
No cutting or modification is needed. Basic hand tools, a drain pan and fresh ATF+4 cover the swap.
