The definition of porosity is: any void or hole found in a casting. These voids can be caused by gases and contaminants present during the casting process and typically occur near the outer parts, or at the top of a casting. Many of your major original equipment manufacturers such as Honda, GM, Chrysler and others, all have had issues with the porosity of some castings.
Typically the voids do not pass all the way through the casting. They can be as large as 3 mm or as small as 0.25 mm. They are most commonly exposed when a surface is machined. What issues can these voids create? They can prevent the gasket from sealing on the machined surface.
These problems can be caught while the vehicle is still under warranty, but sometimes porosity problems occur as the gasket ages and hardens. If there are a large number of voids, fluids can flow through them and eventually seep in between, leading to leaks, but nothing more significant than a few drops on your garage floor.
How to Detect Porosity
So how does one detect if there’s a leak due to porosity in their engine? There are three methods. First, dyes can be added to the oil. As the oil seeps out in the areas of failure, using a specific type lighting, you will observe the dye. Second, you can pressurize the system with compressed air and look for leaks with a brush and soapy water. Caution: do not over pressurize the system, as it could cause severe gasket failure. Third, using athlete’s foot spray, you can spray an area and examine it for leaks. The powder will puff out in the areas of the leaks.
How Can Porosity Be Fixed?
First, you can apply RTV sealant, or epoxy compound, to the voids and mating area. Excess sealant can clog oil passages in the lifters and variable valve timing components, so be sure to clean the areas on the mating surface completely before installing any new gaskets. This may work for a front cover, but will not work for a complete engine block. Second, you can replace the component. Third, you can use better gaskets. Most gasket manufacturers are aware of porosity problems, since it has been around for years, so you can use better materials to seal a surface.
Cleaning the mating surface with an abrasive disc is recommended, however, grinding away at the mating surface can and will remove metal, causing more leaks and maybe exposing more voids.
Do Aftermarket Parts Have Porosity?
Yes, porosity can be a problem with aftermarket parts, especially if they are made of aluminum. If you ever encounter an aftermarket part that shows signs of porosity, return it.
GM’s LS Engines’ Problems with Porosity
Porosity was a major problem for GM on its LS V8 engines made between 2004-2011 that used aluminum blocks. There were so many failures with this engine that GM issued a TSB, 05-06-01-034. On inspection, the oil leak may appear to be a failed oil pan gasket or leaking rear main seal, but the source of the leak is actually the oil crossover port above the camshaft that is sealed by the rear cover.
GM recommends replacing the rear cover if there are a lot of voids on or near the mating surfaces. If voids are on the block, GM recommends using RTV fill to seal the voids. Use a high quality gasket in these applications. Aftermarket gaskets are available to solve this problem.
Honda had a porosity problem on their V6 1998-2003 engines. This leak occurred in the valley of the engine and can cause leaks at the front, middle or rear of the engine. Honda’s solution is JB Weld. Apply it to the block area of the leak.
So, if you are replacing your head gasket, water pump, or even the intake and oil pan gaskets, check for porosity. It could save you many hours of frustration trying to seal a leak.