Hi there William,
The issue you're experiencing with your GMC Sierra can indeed be perplexing. White smoke from the exhaust, especially when it's not consistent, can have several causes aside from a blown head gasket. Here are a few possibilities:
- Condensation in the Exhaust System: This is common, especially in colder weather, and typically resolves as the vehicle warms up.
- Valve Seal Issues: If the smoke appears more prominently after the vehicle has been sitting, bad valve seals could be the culprit.
- Coolant Leak: Even though you haven’t noticed a drop in coolant levels, a small leak might not be immediately obvious.
- Fuel System Issues: Over-fueling or problems with fuel injectors can sometimes cause white smoke.
- Engine Oil Consumption: If oil burns along with fuel, it can produce white smoke. This might indicate an issue with the engine's oil system.
Given the intermittent nature of the smoke and the fact that your coolant levels are stable, a minor issue in the valve seals or a slight inconsistency in the fuel system seems more likely than a blown head gasket. However, diagnosing such issues can be complex and often requires a professional look.
It's advisable to get your vehicle checked by a mechanic at your earliest convenience. They can perform a pressure test and check for any diagnostic codes that might point to the root cause. Remember, while it's tempting to seek quick fixes, it's crucial to diagnose and address the underlying issue to avoid further damage to your vehicle.
Hope that helps :-)
Zack - Motor Verso Mechanics Team