Lead Leaching in Caterpillar Stationary Gas Engines
We commonly understand that if only copper appears in oil analysis results from a new diesel or stationary gas engine with less than 3,000 hours of run time, the source is most likely copper leaching from copper coils in the oil cooler.
So, how do we interpret stationary gas engine oil analysis results when only lead appears (commonly between 3,000 hours and 7,000 hours)? This occurrence is non-wear leaching of lead from main and crank bearings. Lead leaching is a common occurrence in Caterpillar stationary gas engines, and only occurs with CAT OEM bearings. Aftermarket bearings have not proven to leach lead.
Caterpillar manufactured standard main and crank bearings are steel backed aluminum bearings with a lead and tin overlay. These bearings often leach lead at levels up to 100 ppm because of the bearing manufacturing process that results in a soft layer of lead and tin. In the instances of lead leaching, there are no significant levels of iron, aluminum, or tin that would indicate plain bearing failure.
There is normally no need to condemn a Caterpillar stationary gas engine crankcase fill of oil based on lead exceeding 100 PPM, if no other wear metals are elevated. However, when leached lead levels climb above 100 ppm, some operators change oil so this level of lead will not mask other problems that could be identified through oil analysis.
Caterpillar also offers “Hard” bearings for their stationary gas engines. These bearings have a higher Brinell Hardness and the lead-tin layer is thinner. As a result, lead does not significantly leach from these bearings. Lead reaching 10 ppm after 12K hours of crankcase oil fill with Caterpillar Hard bearings is a normal level of lead.
History and lab testing has shown that non-wear leaching of lead does not shorten mainframe life. At a Caterpillar engine end of life, there is no difference in wear between the engines that leached lead and the engines that did not. During extensive laboratory testing on a Caterpillar engine, elevated lead levels were reproduced during simulated extended drains. The technicians would verify weights and measurements of all wear parts prior to building the engine and after the engine test runs. They were unable to identify any additional wear when also simulating lead leaching.
Some Operators may be fearful of the elevated levels of lead, regardless of the fact that there were no other wear metals, because they do not want a high concentration of lead circulating through and abrading their engine. In this case, a micropatch test can be performed on an engine oil sample to see if there are harmful bearing wear metals in circulation.
Following, are a Data Analyst’s Comments on an oil analysis report after reviewing micropatch results on a sample with elevated lead per Inductively Coupled Plasma (ICP) elemental analysis:
No maintenance or corrective action suggested at this time. Moderate amount of abrasives (silica/dirt and environmental contaminants). Minor amount of ferrous rubbing wear. Rubbing wear can result from breakdown of larger particles in a system with a fault present. Copper and lead do not appear to be wear in this sample. Possible sources could be lubricant coolers, pipes and solder connections.
In summary: The appearance of lead in your Caterpillar stationary gas engine oil analysis results, with no other wear metals present, is not a primary reason to change oil.
Thank you Howard, Jon, Peter, Kevin, and Clint for your contributions to this Tech Tip.