Excessive White Smoke
Several things could be causing white smoke in your Mack Semi:
Problem: Stiction in the injectors
Problem: Poor fuel quality
Problem: Glow plug problem
White smoke can be caused by a couple of different things. If there is only smoke on startup, which goes away when the truck gets warmed up, it is likely unburned fuel. An injector with stiction can cause an issue where the combustion temperatures are not high enough to completely burn the fuel. Using one full dose of Stiction Eliminator to clean out your injectors will give your truck a boost when cold. Poor fuel quality can cause water in the fuel without you realizing it. If the “water in fuel” light is on, or you just suspect water in the fuel, use Diesel Extreme to clear out the system and change your fuel filter.
If your truck is using excessive coolant and smoking white all of the time, this can be a sign of a blown head gasket, but this is not common in these trucks. If it is coolant, the exhaust will have a sweet smell to it.
To differentiate between coolant and fuel: If the exhaust smells slightly sweet, it is coolant. If it smells almost like bug spray, it is unburned fuel.
A glow plug problem can also cause white smoke. Check out all the wiring leading to the glow plugs for chaffing or breaks, and check the resistance across the glow plug itself.