1987/07/01 Caterpillar

All Caterpillar Truck Engines

Reference: Truck Engine News; November, 1986, Page 3; "New Indicator Instrument Group Available To Measure Crankcase Blowby And Radiator Air Velocity " on all Caterpillar Truck Engines

Reference: Special Instruction SEHS8712, "Using The 8T2700 Blowby/Air Flow Indicator Group ".

There have been questions regarding the use of the engine blowby meter and interpretation of the measurements obtained. The following guidelines will assist users with these matters. Add a note to the referenced Special Instruction referring to this article.

Use the data obtained by the blowby meter only as additional information concerning engine condition and NOT as a stand alone good/bad indicator of engine condition. Do not use the data alone to determine if the engine should be rebuilt. Other indicators such as high oil consumption, low power, hard starting, and excessive fuel consumption must be considered.

Read the blowby rate at full engine rpm, either at no load or full load. On some engines, the no load blowby may vary as much as 100% from the full load blowby. Use the highest reading for the actual blowby value.

In addition to the known previous corrections to the blowby table, the MAXIMUM allowable rates for the blowby ranges for some other engine families are too low. More accurate data will be announced when available. More engines will also be added to the table when accurate data is obtained.

After a new engine is used for a short time, the blowby can decrease as the rings are seated. Also, a newly rebuilt engine can have a high blowby rate because of factors such as the rings not being properly seated, or worn parts which were not changed such as valve guides.

As stated on Page 10 of the Special Instruction, the meter is sensitive to high frequency engine noise. To avoid incorrect readouts, keep the pickup as far from the engine as possible when making blowby measurements. Do not put the pickup near the turbocharger or fan blades as this can cause a reading error.

The combination blowby/air flow meter.

Also, make the following corrections to the Special Instruction:

NOTE: Several early indicators were shipped with only temporary instructions in the box. Scrap the temporary instructions and replace them with the referenced form SEHS8712.

... On Page 2, in the list of repair parts for Item (7), change "8T0899" to "8T0999".

... On Page 11, in the second paragraph, change the word "one" to the word "two". In the same paragraph, change the number "1" after the equal sign to "2". This doubles the MAXIMUM allowable blowby rate for a new engine.

... Also on Page 11, make two changes in the table under the heading "Blowby Range" for both types of the 3204 Engines. The recommended range for ALL 3204 Engines is now 52 to 104 L/Min (110 to 220 cu ft/hr).