2019 Chevy Colorado Thermostat Replacement (2.8L Duramax Diesel)

Here's exactly how I replace the thermostat on a 2019 Chevy Colorado with the 2.8L Duramax diesel — and the number one thing I want to warn you about upfront: the thermostat is not in an obvious location. First-timers spend significant time looking in the wrong place.

What You'll Need

• Thermostat replacement kit: ACDelco 131-170 or OEM equivalent (includes thermostat, gasket, and housing bolts)
• 10mm socket
• 13mm socket (coolant housing bolts)
• 3/8" drive ratchet and extensions
• Torque wrench
• Coolant drain pan (at least 2-gallon)
• Funnel
• Dex-Cool Extended Life coolant (50/50 premix preferred — the 2.8L Duramax uses Dex-Cool orange, approximately 2.5-gallon total system capacity)
• Hose clamp pliers
• New O-ring or gasket (typically included in the thermostat kit)

Estimated time: 60–90 minutes Estimated cost: $35–$65 in parts (vs. $250–$400 at a Chevy dealer)

The Key Gotcha: Where the Thermostat Lives on the 2.8L Duramax

On most gasoline engines, the thermostat is on the driver's side near the upper radiator hose — that's where most mechanics look first. On the 2019 Chevy Colorado 2.8L Duramax diesel, the thermostat is housed inside the coolant housing on the passenger side of the engine, toward the rear of the engine compartment.

The coolant housing is a plastic/aluminum assembly that connects multiple coolant lines. The thermostat sits inside this housing, sealed by an O-ring or gasket. You access it by removing the housing, not by following the upper radiator hose as you would on most gas engines.

Symptoms that indicate a failing thermostat on the 2.8L Duramax:

• Engine taking unusually long to reach operating temperature
• Heater blowing lukewarm air in cold weather
• Temperature gauge fluctuating (thermostat opening/closing erratically)
• Overheating (thermostat stuck closed — more urgent)

Step-by-Step Instructions

1. Let the engine cool completely — Never open the cooling system on a hot diesel. The 2.8L Duramax cooling system is pressurized. Wait 2+ hours after driving.
2. Locate and remove the coolant pressure cap — On the Duramax Colorado, the coolant reservoir is the pressurized surge tank. Remove the cap slowly — check for pressure even on a cold engine.
3. Drain enough coolant — You don't need to drain the entire system. Drain approximately 2–3 quarts by opening the radiator drain petcock (bottom of radiator) into your pan. This drops the coolant level below the thermostat housing.
4. Locate the thermostat housing on the passenger side — Trace the coolant hoses on the passenger side of the engine toward the rear of the engine compartment. The thermostat housing will have 2–3 coolant hoses attached to it and is secured to the engine block with bolts.
5. Remove the coolant hoses from the housing — Use hose clamp pliers to slide the clamps back on each hose, then twist and pull the hoses free. Have rags ready — residual coolant will spill.
6. Remove the housing bolts — Typically two or three 10mm or 13mm bolts securing the housing to the engine block or cylinder head. Remove all bolts and set aside.
7. Remove the coolant housing — Pull the housing away from the engine. The thermostat will either be inside the housing or seated in the engine block opening revealed by removing the housing.
8. Remove the old thermostat — Note the orientation of the thermostat (which way the spring faces — toward the engine). Remove the old gasket or O-ring from the sealing surface and clean the surface with a rag.
9. Install the new thermostat — Install the new O-ring or gasket. Seat the new thermostat with the spring end facing the correct direction (toward the engine block, same as the original). Many Duramax thermostats are indexed — they only go in one way.
10. Reinstall the coolant housing — Position the housing, start all bolts by hand, then torque to 89 in-lbs (10 Nm) for the plastic housing bolts. Do not over-torque plastic housing bolts — they will crack the housing.
11. Reconnect coolant hoses — Reconnect all hoses and slide clamps back into position.
12. Refill coolant — Add Dex-Cool 50/50 premix to the surge tank to the MAX COLD line.
13. Bleed air from the system — Start the engine, leave the surge tank cap off. Let the engine reach operating temperature. Keep the level at MAX as air works out. When no more air bubbles appear and the level stabilizes, install the cap.
14. Verify normal operating temperature — The 2.8L Duramax should reach normal operating temperature (approximately 195°F / 90°C) within 5–8 minutes of cold start.

Common Mistakes to Avoid

• Looking on the driver's side for the thermostat — It's on the passenger side, inside the coolant housing. Don't waste time following the upper radiator hose.
• Over-torquing the plastic housing bolts — 89 in-lbs is the spec. A cracked coolant housing is a bigger repair than a thermostat.
• Not bleeding air from the system — Air pockets in a diesel cooling system cause hot spots and inaccurate temperature readings. Run the engine with the cap off until the level stabilizes and no bubbles remain.
• Using the wrong coolant — The 2.8L Duramax uses Dex-Cool (OAT orange), not universal green coolant. Do not mix types.

For the full 2019 Chevy Colorado maintenance guide — oil changes (Duramax requires Dexos-D diesel spec), fuel filter, brakes, transfer case fluid — get the full repair library at OwnerDrop — starting at $29.99/mo.

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Related guides: How to diagnose car overheating | How to flush your radiator — beginner's guide