THERMOSTAT AS 4973990 - Caterpillar

Probable Causes
Failed turbocharger seals
Worn valve guide seals or faulty valve guide seals
Worn valve guides
Worn piston rings
Scored cylinder liners or worn cylinder linersRecommended Actions
Failed Turbocharger Seals
Check the inlet manifold and the exhaust manifold for oil. If oil is present, replace the turbocharger.Worn Valve Guide Seals or Faulty Valve Guide Seals
Inspect the valve guide seals for wear and for damage. Replace the valve guide seals, if necessary.Worn Valve Guides
Inspect the valve guides for wear. Refer to the Specification manual for the maximum permissible wear of the valve guides. If necessary, recondition the cylinder head.Worn Piston Rings
Piston rings that have excessive wear can cause too much pressure in the crankcase. The additional pressure in the crankcase will cause more than the normal amount of crankcase blowby from the crankcase breather. Use the 8T-2700 Blowby/Air Flow Indicator to check the amount of crankcase blowby. The test procedure is in Special Instruction, SEHS8712. Inspect piston rings and install new parts, as required.Scored Cylinder Walls or Worn Cylinder Walls
Inspect the cylinder liners for damage. Hone the cylinder liners in order to remove the scoring. If necessary, install new liners.