* Improper Head Gasket Installation: This is the most likely culprit. If the head gasket wasn't installed correctly (e.g., damaged gasket, warped head or block, incorrect torque sequence or value, improper cleaning of surfaces), coolant can leak into the cylinders. This causes the white, steamy smoke you're seeing.
* Cracked Cylinder Head or Block: Even with a new head gasket, a pre-existing crack in the cylinder head or engine block could still allow coolant to leak. This would be present even *before* the head gasket replacement, but might have gone unnoticed until the engine was disassembled. A pressure test is needed to check for cracks.
* Damaged Cylinder Head: During the removal and reinstallation of the cylinder head, it's possible the head itself was damaged (cracked or warped). This needs to be checked for warpage with a straight edge.
* Coolant in the Oil: If the coolant is leaking into the crankcase (rather than directly into the combustion chamber), you might see white or milky smoke, but it might not be as immediately obvious as smoke from the exhaust. This would also contaminate the engine oil, giving it a milky appearance. Check your oil dipstick!
* Incorrectly Installed Head Bolts/Studs: If the head bolts or studs were improperly installed (over-tightened causing damage, or under-tightened leading to leaks), this could cause a leak.
What to do:
1. Check the engine oil: Does it look milky or have a frothy consistency? This indicates coolant in the oil, a serious problem.
2. Inspect the coolant: Look for any signs of oil contamination (a greasy sheen).
3. Pressure test the cooling system: This helps pinpoint coolant leaks.
4. Have a compression test performed: This will check the integrity of the cylinders.
5. Re-inspect the head gasket installation: If possible, have a qualified mechanic re-check the work. This requires removing the head again, but is far better than continuing to run a damaged engine.
Simply replacing the head gasket doesn't guarantee the problem is solved. Proper diagnosis and potentially further repairs are likely necessary to fix the smoking issue. Continuing to drive the truck while it's smoking heavily will likely cause further damage.
