Hellcat Thermostat Buying Guide
TL;DR: The supercharged 6.2 Hemi runs two separate cooling loops — the normal engine coolant loop, which has the thermostat in it, and a low-temperature loop that feeds the charge air cooler and has no thermostat at all. Most people shopping for a "Hellcat thermostat" because of heat soak are shopping the wrong circuit. On the engine loop, the part you actually buy on most late Gen III Hemi applications is a housing assembly with the thermostat sealed into it, not a bare disc you drop into an old housing. And a colder-than-stock thermostat does not lower intake air temperature, does not lower the temperature the engine sees under load, and is not a performance part on this platform.
Know which cooling circuit you are actually fixing
This is the single thing that decides whether you buy a thermostat at all.
The 6.2 supercharged Hemi has a conventional engine cooling system: water pump, block and heads, radiator, thermostat, coolant temperature sensing feeding the PCM. That circuit is what the thermostat regulates, and it exists to get the engine to operating temperature quickly and hold it there.
It also has a second, independent low-temperature circuit. A separate electric coolant pump moves coolant through the heat exchanger built into the supercharger and out to a low-temperature radiator at the front of the car. That loop is what controls charge air temperature — the temperature of the air leaving the blower on its way into the intake. It runs its own pump, its own reservoir and its own heat exchanger, and it is not regulated by the engine thermostat.
The practical consequence is blunt. If your complaint is intake air temperature climbing on back-to-back pulls, timing being pulled after a run, or the car feeling soft once it is heat soaked, the engine thermostat has nothing to do with it. That is the low-temp loop — its pump, its coolant level, airflow through the low-temperature radiator, or simply the thermal mass of the system. Replacing the engine thermostat will change nothing you can feel.
If your complaint is the engine running hot on the gauge, running cold and never reaching temperature, weak heat from the vents, a coolant temperature code, or a visible coolant weep at the front of the engine — now you are in thermostat territory. Start in thermostats and housings and read on.
What you are actually buying: housing assembly vs standalone thermostat
Late Gen III Hemi applications generally moved to an integrated design where the thermostat is sealed into a molded housing, frequently with the coolant temperature sensor and the outlet necks as part of the same assembly. You do not open it, you do not swap the disc, and there is no separate thermostat gasket to buy — the sealing element is part of the assembly. Earlier and other Hemi variants used a serviceable thermostat in a separate housing.
Do not guess which one your car has. Confirm the current part number for your exact model year and application against the manufacturer catalogue before you order, and check whether the listing includes the temperature sensor or expects you to transfer yours. That one detail is the most common reason a cooling job stalls halfway with the car apart.
Two more checks worth doing before you click buy:
- Sensor included or not. If the housing carries the coolant temperature sensor and the kit does not include one, plan on transferring the original. If the original is a press-in with a retaining clip, have a fresh clip and O-ring on hand — see gaskets and seals.
- Hose necks and clip style. Integrated housings are application-specific in their outlet geometry. A housing that bolts to the engine but points a neck the wrong way is a returned part.
Why a colder thermostat is not an upgrade here
The colder-thermostat idea comes from an older world where coolant temperature directly limited timing and a lower opening temperature meant a cooler engine everywhere.
On a modern supercharged Hemi, three things break that logic.
The calibration targets a temperature, not a thermostat. The engine management strategy is built around a normal operating coolant temperature. Drop the opening temperature and, under any real load, the cooling system is already well past that opening point — the thermostat is wide open and the radiator is the limiting factor, so the peak temperature you see on a hard pull barely moves. What you do change is warmup and cruise behaviour, where the engine now runs colder than the calibration expects.
Colder is not free. An engine held below its designed operating temperature runs richer, wears more, dilutes oil with fuel faster and makes less heat for the cabin in winter. On some applications a coolant temperature that never reaches the expected threshold will set a thermostat-performance code.
It is the wrong circuit anyway. Charge air temperature — the number that actually costs you timing on this engine — is governed by the low-temp loop, the supercharger heat exchanger and the low-temperature radiator. The engine thermostat does not touch it.
Buy the correct opening temperature for your application, whatever the service data specifies. If you want lower charge air temperatures, spend the money on the low-temp side of the system instead.
Symptom-to-part table
| Symptom | Most likely cause | What to buy |
|---|---|---|
| Slow to warm up, weak cabin heat, code for insufficient coolant temperature | Thermostat stuck open | Thermostat or housing assembly |
| Temperature climbs in traffic, drops at speed | Airflow: fan operation, debris in the radiator core, condenser blockage | Diagnose first — not a thermostat |
| Temperature climbs everywhere, quickly, after a normal warmup | Thermostat stuck closed, or air trapped in the system after a previous coolant job | Thermostat assembly, then a proper fill and bleed |
| Coolant weep or crust at the front of the engine, no overheating | Cracked plastic housing or a failed seal at the housing face | Housing assembly plus gaskets and seals |
| Whine or coolant weep from the pump, temperature unstable | Water pump bearing or seal | Water pumps |
| Erratic temperature reading, fans behaving oddly, no actual heat problem | Coolant temperature sensor or its connector | Engine sensors |
| Intake air temps climb on repeated pulls, timing pulled, car soft when hot | Low-temperature charge air circuit — pump, level, airflow | Not a thermostat. Diagnose the low-temp loop |
Doing the job right
Three things separate a clean cooling repair from one you do twice.
Bleed it properly. The single most common cause of "it still overheats after I replaced the thermostat" is trapped air. Follow the fill and bleed procedure in the service manual for your car, including any bleed points and the specified engine-running sequence. An air pocket sitting against the thermostat will keep it from seeing hot coolant and will happily convince you the new part is defective.
Use the specified coolant. Modern Mopar cooling systems are specific about coolant chemistry, and mixing types is how you end up with gelling and heater core problems a year later. Use what the manual calls for, at the specified concentration.
Torque to the sequence in the manual. Plastic housings on aluminium are unforgiving. Overtighten one bolt and you distort the flange, crack the housing, or start a leak at the far corner. Torque in the factory sequence to the value in the service manual — not by feel, and never with an impact.
While you are in there, look at the rest of the front of the engine. If the housing failed at high mileage, the water pump, the hoses and the pressure cap are the same age and the labour overlaps. Platform parts live in Hellcat 6.2 supercharged parts, and the broader family is in Gen III Hemi parts.
Frequently Asked Questions
Does the Hellcat have one thermostat or two? One thermostat, in the engine cooling circuit. The low-temperature charge air cooler circuit is a separate loop with its own electric pump and its own radiator, and it is not thermostatically regulated the way the engine loop is.
Will a colder thermostat lower my intake air temperatures? No. Charge air temperature is controlled by the low-temperature loop and its heat exchanger, not by the engine thermostat. A colder thermostat changes warmup and cruise coolant temperature and does nothing measurable to intake air temperature.
Can I just replace the thermostat disc instead of the whole housing? Only if your application uses a serviceable thermostat in a separate housing. Many late Gen III Hemi applications seal the thermostat into the housing assembly, in which case the assembly is the service part. Confirm the current part number for your model year against the manufacturer catalogue before ordering.
My car is overheating. Is it the thermostat? Maybe, but check coolant level and airflow first. A thermostat stuck closed overheats consistently and quickly after warmup. Overheating only in traffic that clears at highway speed points at fan operation or a blocked radiator core, not at the thermostat.
Why did my temperature never come back to normal after I changed the thermostat? Almost always trapped air. Redo the fill and bleed procedure exactly as the service manual specifies for your car before you condemn the new part.
Does the coolant temperature sensor come with the housing? It depends on the listing. Some housing assemblies include it, some expect you to transfer the original. Check before you order so you are not stuck mid-job waiting on a sensor.
Is the water pump worth doing at the same time? If the car is high mileage and the front of the engine is already open, it is cheap insurance in labour-hour terms. A pump that is already noisy or weeping should not go back in behind a new housing.
Sources
Written against the published architecture of the supercharged 6.2 Gen III Hemi cooling system — the engine coolant loop and the separate low-temperature charge air cooler loop with its own electric pump and front-mounted heat exchanger — general Gen III Hemi thermostat housing service practice, and our own counter experience with housing leaks, bleed-related comebacks and misdiagnosed heat soak complaints on this platform. Opening temperatures, torque values, coolant specification and part numbers are deliberately not quoted here: pull them from the current factory service manual for your exact model year, and confirm the part number against the manufacturer catalogue before ordering.
Questions on fitment for your car: sales@coretransmissionparts.com. Orders over $70 ship free.