1936-1942 Plymouth Service Manual Recommendations

Engine Oil Recommendations

1. The recommendations shown on the "Table of Capacities, Frequencies, and Lubricants" are based on the principle that lower viscosity oils circulate more rapidly and lubricate parts with closer clearances more readily than heavier oils. Complete satisfaction, however, depends upon the use of only well refined high quality products.
2. For cars of comparatively low mileage, SAE 20 or No. 20-W Engine Oil is recommended as a general summer oil. Either grade may be used in tropical climates during the winter months or No. 20-W Engine Oil may be used in localities where only very mild winter conditions prevail, such as territories where temperatures never go below 10°F above zero. If, however, as a result of continued high speed driving or other causes, oil consumption becomes a factor, SAE 30 Engine Oil may be used for temperatures above 32°F above zero.
3. No. 10-W Engine Oil is recommended as a general winter oil for temperatures as low as 10°F below zero, but no lower. However, should atmospheric temperatures rise above +32°F during winter, No. 10-W is satisfactory, and a change is not necessary until the next mileage period. No. 10-W Engine Oil may also be used during summer, if desired provided driving habits are moderate.
4. For sub-zero winter conditions, such as in temperatures below -10°F, No. 10-W Engine Oil should be diluted with 10% colorless, refined kerosene, which should be thoroughly mixed with the oil before it is added to the engine.

When to Change Engine Oil

1. Oil changes should be made, under normal conditions, every 1500 to 2000 miles during winter and every 2500 to 3000 miles during summer. It is always advisable to drain the oil while the engine is at normal operating temperature, because the oil will drain more completely when hot, carrying more of the foreign material and dirt with it.
2. During the winter, the engine oil should have a pour point or cold test below the lowest temperature that will be encountered during its use. If the car is driven for short distances of only a few miles at a time, moisture in the crankcase will condense and form a sludge which may freeze and clog the oil inlet screen. This condition is greatly aggravated by extremely low temperatures extending for a long period of time. Under driving conditions of this type, the engine does not become sufficiently warm to expel the moisture through the crankcase ventilator. Therefore, under these conditions, the oil should be changed every 500 miles to eliminate sludge.
3. An alternative to this frequent change period during the winter in an occasional drive of 30 miles or more which will help to eliminate water accumulation through the crankcase ventilation system. If the car is driven in this manner frequently, the oil may be changed at the normal recommended winter change period of 1500 to 2000 miles.

Replacement of Oil Filter

Install a new oil filter, a new oil filter cartridge (if equipped with the replaceable cartridge type) every 8000 miles. In dusty areas, it may be advisable to change filter, or cartridge, at any time when the oil appears excessively dirty.