Jun 162011
 

I have a 1997 Jeep Grand Cherokee Limited 5.2L V-8, about 253K miles.  Used oil analysis is showing very high nickel (24 ppm in oil used for 3270 miles).  A previous test done 61k miles earlier was high but not critical (11 ppm in 2045 miles).  Both tests show very low levels of other wear metals, well in the normal range.  Does anybody know what parts in this engine may be coated with or plated with nickel that might be wearing out?

  2 Responses to “Oil analysis for 1997 Jeep 5.2L shows high nickel others OK”

  1. Cylinder wear is something you want to minimize in an engine, so in some applications, the inside surface of the cylinders are coated with a hard, wear-resistant material such as nickel and silicon carbide. Such coatings go under various names, such as “Nikasil” (Mahle Corp.), “Nicom” (U.S. Chrome Corp. of Wisconsin), “NSC” (Millennium Technologies) and others that all use a proprietary blend of nickel and silicon carbide to plate cylinders.

    Nickel is the “glue” that holds and supports the particles of silicon carbide on the cylinder wall surface. Silicon carbide is a very hard abrasive material with a hardness second only to diamond. According to one company who uses the process, the coating has a hardness rating of 600 on the Vickers scale, and a sliding hardness of 58 to 60 Rockwell C. The hardness combined with a tendency to attract and hold oil (“oleophilic”) makes these coatings highly wear resistant. To keep it from wearing the piston rings, though, the size of the silicon carbide particles must be very small, typically around 3 to 4 microns in diameter. The particles make up only about 4 percent of the coating.

    Read More Here: http://www.enginebuildermag.com/Article/36521/machining_new_metals__nickel_silicon_carbide_coatings.aspx

  2. Thanks very much for the comment about nickel cylinder coatings, I suppose this could be the issue. Can anybody tell me if Jeep used this kind of coating on 1997 5.2L V-8’s? It is the original engine and has never been taken apart for repairs, so if there is a coating, it would have been factory applied.

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