Checking Engines for Source of Excessive Smoking

Smoke Test

  1. Start engine; run engine approximately 5 minutes at normal idle
    • Accelerate engine several times, watch for excessive blue-gray smoke at the tail pipe. Repeat above procedure several times. Should blue-gray smoke continue to appear at the tail pipe this will indicate oil is getting into the combustion chamber through the vacuum booster pump, vacuum type breather, past the valves or various other reasons.
  2. At this point a process of elimination should be started.
    • Start with the vacuum booster pump (when used). A porous or damaged booster pump diaphragm will allow oil to be pulled into the intake manifold through the vacuum line running from the pump to the manifold. Disconnect vacuum line at the pump and manifold, check the connections and line for an oil deposit. Should oil be found in the line, the pump must be replaced. After replacing pump start engine and run at a fast idle for 20 to 30 minutes, accelerate the engine several times during this period. If excessive engine smoking ceases, the problem has been resolved. CAUTION: Should the blue-gray smoke continue after the pump is replaced the above procedure should be repeated as new or rebuilt pumps are occasionally found to be faulty.
  3. Vacuum operated crankcase breather.
    • This type breather system is standard equipment on many engines. We have had various types of installations and control valves in use. All types control the amount of air drawn through the crankcase by use of a control valve located between the intake manifold and the crankcase or the valve chamber cover, and is connected to a vacuum line. If the control valve becomes worn or stuck in the open position the engine will consume large quantities of oil. To check, disconnect the vacuum line at the control valve. Remove the valve. If oil is found in the valve this indicates oil is being pulled into the combustion chamber. Replace the valve. Do not take a chance on the old valve. After replacing the control valve, start the engine. Repeat the smoke test as outlined in Step Two.
  4. Checking valve chamber ventilating tube.
    • Some vehicles are equipped with a tube from the valve chamber cover to the air cleaner which ventilates the valve chamber. In some cases the air cleaner will pull oil through the ventilating tube during periods of high air flow. Excessive oil and oil vapors in the valve chamber will also add to the problem. TO CHECK: Disconnect the ventilating tube and inspect for an oil deposit in the tube. When oil is found, the correction of this condition may require a longer ventilating tube and relocation of the ventilating tube connection on the air cleaner, and proper servicing of the valve train.
  5. Oil loss through valve guides.
    • There are various methods used to lubricate the rocker arm shafts on 0. H.V. engines. For this reason it is important to know the methods used so the oil flow can be shut off, while a smoke test is made.
      • (A) External tube running from the oil galley up to the rocker arm shaft. Disconnect the tube and plug the line is all that is required to shut off the oil to make a smoke test.
        On V-8 engines three methods are used to shut off the oil.
      • (B) One is to bring the oil up through a drilled passage in the shaft bracket. To shut off the oil flow in this system loosen the bracket and slip a shim under the bracket restricting the oil passage.
      • (C) Another method is to use a drilled hold down bolt in one of the shaft brackets, which allows the oil to pass up through the bolt to the shaft. To restrict the flow of oil in this system, remove the drilled hold down bolt and replace with a solid bolt while smoke test is made.
      • (D) Another method is use of undercut hold down bolt. The center section being smaller than the drilled hole in the shaft bracket which allows the oil to flow to rocker arm shaft. To restrict the flow of oil the undercut bolt can be replaced with a solid bolt while the smoke test is being made.
      • (E) Canoe type rocker systems are lubricated from the valve lifter through hollow push rods. Clips are available from your jobber to stop oil from the overhead.
        After restricting the oil flow as listed in A-B-C-D & E make a smoke test as outlined in Step Two. If excessive smoke ceases it will be necessary to make corrections. 
  6. Further Checks
    • (A) On some V-8 engines the intake manifold serves as the tappet chamber cover. A defective gasket at this point will allow vacuum to draw oil from the tappet chamber-replace gasket-carefully torque head and manifold bolts.
    • (B) High oil level or high oil pressure will flood the cylinders with excessive oil, either or both must be corrected.

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