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1994-2008 Dodge Ram 1500/2500/3500 Pickup Truck Thermostat Replacement

Dodge Ram Truck Digital Manual

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This page is taken directly from our digital online manual 30042 for the 1994-2008 Dodge Ram 1500, 2500, and 3500 pickup trucks, 2WD or 4WD with gasoline or diesel engines. The thermostat is important to keep the truck running properly, not overheating or running too cool. There is no set interval when you should replace the thermostat, but if you are draining the coolant for another reason, or replacing radiator hoses, you should consider the thermostat as well. 60,000 miles or 5 years is a good guideline.

Engine Thermostat Replacement

This video is specifically for the Cummins Diesel engine, the gasoline V6, V8, and V10 engine are similar

See more specific instructions below for all gasoline engines.

Warning: Do not remove the radiator cap or expansion tank cap, drain the coolant or replace the thermostat until the engine has cooled completely. 


  1. Disconnect the cable(s) from the negative battery terminal(s) - Diesel engines have two batteries - and set it aside to avoid accidental reconnection.

  2. Drain the cooling system via the petcosk or by removing the lower radiator hose. If the coolant is relatively new or in good condition, save it and reuse it.

3.7L V6 and 4.7L V8 engines

  1. Raise the vehicle and support it securely on jack stands.

  2. (See illustration) Follow the lower radiator hose to the engine to locate the thermostat housing.


3.7L V6 thermostat housing

Thermostat housing location on the 3.7L V6 engine (the 4.7L V8 is similar) - view here is from below at the front of the engine


Hemi V8, Cummins Diesel and 8.0L V10 engines

  1. On 1998 and earlier diesel models, unbolt the alternator and alternator mounting bracket, then set it aside for access to the thermostat. Full detailed instructions for this are in Chapter 5 of the Haynes manual.

  2. (See illustrations) Follow the upper radiator hose to the engine to locate the thermostat housing. 


Hemi V8 thermostat housing

Thermostat housing location on the Hemi engine - the air conditioning compressor is removed for clarity

Early diesel engine thermostat housing

On 1994 through 1998 diesel engines, the alternator bracket (large arrow) must be removed, then remove the bolts (three small arrows) and lift the thermostat cover off


3.9L V6, 5.2L V8 and 5.9L V8 engines

  1. Remove the alternator bracket and the alternator. Full detailed instructions for this are in Chapter 5 of the Haynes manual.
    Note: On 4WD models, unplug the 4WD indicator lamp harness located behind the alternator.
  2. Follow the upper radiator to the engine to locate the thermostat housing.

All models

  1. Squeeze the tabs on the hose clamp to loosen it from the hose(s), then reposition the clamp several inches back up the hose. Detach the hose(s) from the thermostat housing.
    If the hose is stuck, grasp it near the end with a pair of adjustable pliers and twist it to break the seal, then pull it off. If the hose is old or deteriorated, just cut it off and install a new one.
    Note: Special hose clamp pliers are available at most auto parts stores.

  2. If the outer surface of the thermostat housing where it mates with the hose is already deteriorated (corroded, pitted, etc.), it may be damaged further by hose removal. If it is, the thermostat housing will have to be replaced.

  3. Remove the thermostat housing from the engine. If the housing is stuck, tap it with a soft-faced hammer to jar it loose. Be prepared for some coolant to spill as the gasket seal is broken.
    Note: On 8.0L V10 engines, a smaller hose and the sensor harness connector must be disconnected from the thermostat cover.

  4. (See illustration) Note how the thermostat is installed (which end is facing up, or out, and the position of the air bleed “jiggle valve,” if equipped) and remove it from the engine.


Hemi engine air bleed "jiggle valve"

Location of the air bleed "jiggle valve" on the thermostat of the Hemi engine


  1. On 3.9L V6, 5.2L V8 and 5.9L V8 engines, stuff a rag into the engine thermostat opening, then remove all traces of old gasket material and sealant from the housing and cover with a gasket scraper. Remove the rag from the opening and clean the gasket mating surfaces with chemical gasket remover, lacquer thinner, or acetone.
  2. On all other models, simply remove the rubber gasket from around the thermostat.
  3. On 3.9L V6, 5.2L V8 and 5.9L V8 engines, install the new thermostat in the machined groove on the intake manifold. Make sure the correct end faces into the engine. Apply a thin, uniform layer of RTV sealant to both sides of the new gasket and position it over the thermostat on the intake manifold.
  4. On 8.0L V10 engines, install a new rubber seal constructed with a metal shoulder (sleeve) into the intake manifold. Apply a small amount of RTV sealant around the edge before installing it. Use a special tool to drive the seal into the manifold.
  5. On all other models, install a new rubber gasket around the thermostat.
    (See illustration) Make sure to align the rubber tab on the inside of the O-ring groove with the notch on the thermostat.
    (See illustration) Then align the rubber tab on the outside of the gasket with the notch on the thermostat housing and insert the thermostat and gasket into the thermostat housing.
    Note: Some models are not equipped with alignment notches on the thermostat. Simply install the rubber gasket around the thermostat.


3.7L V6 gasket with rubber tab

On 3.7L V6 engines, align the notch on the thermostat with the rubber tab on the gasket’s inner groove…

3.7L V6 thermostat gasket tab

…then align the tab (lower arrow) on the outer edge of the gasket with the notch in the thermostat housing (upper arrow) and insert the thermostat into the housing.


  1. Install the thermostat housing and bolts onto the engine. Tighten the bolts to the torque listed in 2E this Chapter's Specifications.
    Note: On Hemi, Cummins Diesel, 3.9L V6, 5.2L V8 and 5.9L V8 engines,  install the thermostat housing with the word FRONT towards the front of the engine. This positions the slightly angled thermostat housing into the correct alignment.
  2. Reattach the hose(s) to the fitting(s) and tighten the hose clamp(s) securely.
  3. Refill the cooling system, full details instructions for this are in Chapter 1 of the Haynes manual.
    Attach all the hose and close the radiator drain petcock, then fill the radiator and expansion tank to the MIN mark with a 50/50 mixture of coolant
    Don't close the tank or put the radiator cap on. Set the heater controls to max, and start and run the engine outside or in a ventilated area.
    Let the engine runs until the thermostat opens (coolant will flow into radiator and the upper hose will be hot).
    Turn off the engine let it cool, and refill the radiator and expansion tank again to the MIN mark.
    Squeeze the upper hose to help remove air, then check coolant level again.
    Replace the radiator and expansion tank caps
  4. Start the engine and allow it to reach normal operating temperature, then check for leaks and proper thermostat operation.