6.6 Duramax Excessive Crankcase Pressure/White Smoke

What is Crankcase Pressure?

The 6.6-liter V8 Duramax is a reliable, proven diesel engine, but it can develop issues over time. Two problems that often affect Duramax engines include a buildup of crankcase pressure and engine blow-by. Learn more about how to detect, prevent and fix Duramax engine blow-by.

What Is Crankcase Pressure in a Duramax?

The crankcase is the main part of an engine, providing housing for the pistons, crankshaft and cylinders. It’s one of the most complex parts of the engine and naturally experiences pressure buildup for multiple reasons.

The pistons and cylinders in the crankcase can contribute to pressure in this component. When a piston moves down a cylinder, it increases the pressure by effectively reducing the size of the crankcase. Usually, however, when one piston moves down, another moves up, so the pressure is mostly equalized. 

One common cause of crankcase pressure is a process called blow-by. Some leakage is common in all crankcases, usually beyond the cylinders’ rings. 

Causes of Blow-By

Blow-by is an issue that can be caused by different things in your 6.6L Duramax. Factors that may cause blow-by include fuel, air, and moisture forced past the rings into the crankcase.

Blow-by develops in Duramax and other diesel engines when the air and fuel in the cylinder have a greater pressure than the oil pan. Some gas leaks beyond the piston rings, making its way into the crankcase. As the pressure builds, it eventually becomes too much and needs a way out.

Piston rings aren’t perfect, so some blow-by is expected and completely normal. Excessive blow-by means that the rings are worn out, destroyed or clinging to the cylinder walls. Blow-by can also be a sign of damage to the pistons or cylinders themselves. 

You can detect excessive blow-by in a few ways. Engine misfiring often indicates an issue, as does rough idling. White smoke from the valve cover opening or the oil-fill tube is one of the most common signs of too much blow-by. To test, put the lid upside down over the tube or valve opening. If you see it pop off right away, there’s excessive pressure in the crankcase. 

You can also look for an oil film around the tube or diluted oil in the crankcase.

In older engines, blow-by can occur due to carbon buildup in the piston’s ring grooves.

Fix Crankcase Pressure & Blow-By

Prevent and Fix Crankcase Pressure and Engine Blow-By

If you see white smoke or other signs of blow-by, fixing the issue will prolong your Duramax engine’s life and minimize the need for costly repairs. The process of fixing blow-by depends on the cause. 

A sticky positive crankcase ventilation (PCV) valve can allow oil into the gaskets, leading to blow-by. If you see engine sludge or black smoke, a sticky PCV can be to blame.

Another fix is to use an additive to improve lubrication and minimize sticking from the piston rings. Stiction Eliminator and FR3 Friction Reducer are two examples of additives that improve lubrication and clean the piston rings on your 6.6L Duramax.

Using the right oil and additives can also help keep excessive blow-by and crankcase pressure buildup to a minimum. Our Blue Diamond PAO oil is a superior-quality synthetic oil that improves lubrication, reduces soot and lowers oil consumption.

Prevent Blow-By in Your Duramax Engine With Help From Hot Shot’s Secret

Hot Shot Secret’s line of oils and additives keeps your Duramax engine in the best possible condition. Our diesel fuel additives and other products such as our specially formulated transmission fluids come backed by a 100% satisfaction guarantee. 

Browse our products online or reach out to a representative for assistance.



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