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We’ve had complaints of recurring oil leaks on some Navistar 7.3L diesel engines. Can you offer any solutions?

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There have been reports of engine oil leaks on 1994-2003 Navistar 7.3L diesel engines. These leaks most often occur shortly after cylinder head service has been completed.


To reduce the likelihood of reccurring leaks, a new end plug and sealing system have been designed. These components are available only in a kit form (p/n 1827535C91). Individual components are no longer available.

To install the plugs, follow these procedures.

  1. Remove and discard old end plug, back up ring and O-ring from cylinder head.

  2. Using a clean, dry, lint-free cloth and brake cleaner, clean cylinder head’s internal threads of dirt, loose particles and any foreign material. Dry thoroughly with a clean, dry, lint-free cloth.

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  • To ensure a proper seal, be sure to prevent any foreign material or brake cleaner from getting into the oil rail passage.

  • Lubricate new back up ring and new O-ring with clean engine oil prior to installation onto new end plug. Install back up ring and O-Ring onto end plug. To ensure a proper seal, be careful, not to get engine oil onto threads of end plug.

  • Apply a small bead of Loctite® No. 277 around threads of the new end plug.

  • Install end plug into cylinder head oil rail port. Tighten to the special torque value of 60 ft.lbs. (81 NM). Do not start engine for a minimum of one hour. This allows the thread sealant to cure.

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    What could be the cause of a mysterious timing belt noise on a 2.0L Hyundai engine?

    1999-2000 Hyundai engines with front timing case assemblies manufactured before 9/22/99 may have a mismachined idler pulley mounting surface that is not parallel with the front face of the cylinder block. This can cause the timing belt to walk off the gears and into the front dust cover. The timing belt rubbing against the front dust cover may cause this noise.

    A frayed or shredded timing belt at the front edge may result. The condition may be caused by the front case and is most likely to occur at low mileage. Replace the front case if this condition exists (idler pulley p/n 21310-23002; timing belt p/n 24312-23201).

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