> Main > Diesel Index > 3rd Gen Maint > Thermostat R&R

24V Diesel Thermostat Replacement

Visit Geno's Garage
for Truck accessories.
Geno's Garage Truck Accessories


Thermostat Removal

CAUTION: Do not operate an engine without a thermostat, except for servicing or testing. An engine with the thermostat removed will operate in the radiator bypass mode, causing an overheat condition.

(1) Drain cooling system until coolant level is below thermostat. The radiator drain is at the bottom of the radiator, just to the right of the intercooler outlet, on the driver's side of the truck.
Graphic number: 08900014

(1a) You may need to loosen the boost line hose clamp to get access to the drain valve. While wiggling the pliers to break the valve corrosion loose, turn the valve CCW and unscrew/pull it out. A 3' piece of 1/4" tubing can be attached to the valve outlet to save the anti-freeze.

Tools : 11mm wrench, pliers

(2) When enough anti-freeze has drained, close the valve and replace the boost hose clamp.

Tighten the clamp to 95 in-lb [11 Nm]

(3) Remove radiator hose clamp and hose from thermostat housing. Slide hose from outlet fitting.

Tools: Clamp Pliers

(4) Remove the three water outlet-to-eylinder head bolts and remove the water outlet connector (Fig. 73).

Tools: 10 mm wrench

1 - Water Outlet
2 - Thermostat Housing
3 - Thermostat

Graphic number: 08900013

(5) Clean the mating surfaces of the water outlet connector and clean the thermostat seat groove at the top of the thermostat housing.

NOTE: Do not let any debris fall into the thermostat cavity when cleaning the gasket surfaces

Tools: Scraper or knife

Graphic number: 08900014

Thermostat Installation

1. Install the thermostat into the thermostat housing.

NOTE: Make sure the thermostat seal is installed on the outer lip (bottom) of the thermostat flange. (See parts diagram below)

Graphic number: 08900094
2. Install the water outlet tube and capscrews.

3. Tighten the capscrews to 18 ft-lb [24 Nm]

Tools: 10 mm wrench



Graphic number: 08900053

4. Replace the radiator hose and clamp.

5. Refill radiator with the appropriate water/anti-freeze mix. Use low-silicate antifreeze that meets ASTM4985 (GM6038M specification) criteria.

Part Numbers
Reference No Part Number Part Name
  3935824 Thermostat Kit
1 3935825 Thermostat
2 3942454 Seal, D Ring

Thermostat operation (for the curious)

Coolant flow through cylinder head.

Coolant flow to heater core.

Thermostat Closed
Thermostat open.