1992/04/20 Caterpillar

Reference: Service Magazine; April 6, 1992; "Engine Oil Recommendations Have Been Changed"

Caterpillar Engine Oil Recommendation

The latest oil recommendation for Caterpillar engines is the new American Petroleum Institute (API) performance category CF-4 (except for 3600 Engines). Oils in this category were originally developed to meet emission regulations for the United States truck engine market. They are now recommended for Caterpillar engines used in other applications because of operation with higher piston temperatures. Both the regulated emissions engines and the engines used in machine, industrial, generator set, and marine applications are operating at higher temperatures. The newer designed engines with the two-piece ferrous/aluminum piston and even engines with the one piece aluminum pistons are operating at temperatures higher than in the past.

The oils meeting this API CF-4 performance must pass the following engine tests:

* Cat 1K single cylinder oil test engine (SCOTE).

Evaluates piston deposits and oil consumption. (New engine test)

* Cummins NTC 400 multi-cylinder engine test.

Evaluates piston deposits and oil consumption. (Same engine test as for API CE oil performance, but more stringent passing criteria)

* Mack T-6 multi-cylinder engine test.

Evaluates piston deposits, oil consumption, ring wear and piston ring groove deposits. (Same as for API CE performance)

* Mack T-7 multi-cylinder engine test.

Evaluates the oil viscosity increase. (Same as for the API CE performance)

* CRC L-38 Test, Labeco single cylinder engine.

Evaluates the bearing corrosion, oxidation and deposit formations. (Same as for the API CE and CD performance)

The oils meeting these engine test requirements are generally oils which have been developed for the newer USA emission specifications. But these oils also perform much better at the higher temperatures in today's higher output engines. As Caterpillar has developed engines for increased power output, piston temperatures have increased. Oils must be used which will perform under these higher temperature conditions. The illustration shows how the test performance for oils has increased with the temperature conditions in today's engines.

X axis = various engine designs. ("A" is earlier engine designs, and "B" is newer engine designs.) Y axis = temperature, from lower temperatures toward the bottom to higher temperatures toward the top. "C" is the relative piston crownland temperature in the 1K engine test. "D" is the relative top ring groove temperature in the 1K engine test. "E" is the relative piston crownland temperature in the 1G engine test. "F" is the relative top ring groove temperature in the 1G engine test.

The information in the illustration shows the need for another Caterpillar single cylinder engine test. The piston temperatures in the 1G test were lower than the temperatures that were actually experienced in the field engines. The 1K engine test also upgrades all the engine hardware (direct injection fuel system and piston design) to better emulate today's engines.

The temperatures shown in the illustration indicate the reason for the recommended change in engine oils. The piston in today's engines and the new engines now being produced are operating at higher temperatures. The oils must be capable of operating at these higher temperatures. Older oil formulations are not capable of performing at these temperatures without producing engine problems.

These "older" oils are failing by allowing heavier piston crownland deposits which can result in the top ring not seating correctly. This can lead to loss of oil control. When the top ring does not function, the combustion gas blowby and oil consumption both increase which can result in further deterioration. As the piston crownland deposits (carbon) build, the clearance between the piston and the liner decreases until the piston crownland carbon deposits begin to rub on the cylinder liner. The carbon deposit buildup will polish the liner (wear off the honing pattern). As the liner becomes polished, the oil is not retained on the liner to provide lubrication to the piston rings and skirt. This can result in scuffing and seizure of these components with serious engine damage.

Therefore, the need for the use of the correct performing oil is critical. If the correct oil is not used, premature engine failure may be a result. This statement is based on the supposition that the engine will operate at loading which will produce the high temperatures. If an engine is operated at very low horsepower, then the temperatures will be low and the oil requirements will be less stringent.

The API CF-4 oil performance may be initially considered as a USA on-highway truck engine oil, but the higher temperatures encountered in the newer engine designs have the same requirements. The Cat 3500, 3176, and 3400 engines used in machines and industrial applications are operating with piston temperatures which require the oils with these higher temperature properties. Even some of the engines of earlier designs, operating at high outputs, need oils with the higher temperature capabilities.

The API CF-4 oils have oil consumption as one parameter in the engine test requirements. The Cat 1K, Cummins NTC 400, and Mack T-6 engine tests all have oil consumption requirements. Multi-grade oils are required to produce the low oil consumption necessary to pass these engine tests. Historically, mono-grade oils will have 20 to 30% higher oil consumption than multi-grade oils. Therefore, API CF-4 oils will be SAE 15W40 and 10W30 viscosity grades. These viscosity grades will provide the necessary oils to cover the ambient temperatures encountered.

The newer oil formulations that meet API CF-4 performance, have more dispersive additives which have better higher temperature effectiveness for preventing carbon deposits. In addition, they have the capability to disperse the contaminants within the oil. But the oil dispersancy does have a life limit. Therefore, any extended oil drain intervals must be closely monitored to insure that the oil is drained before the additive effectiveness is depleted.

Fuel Sulfur and Oil TBN

When the Caterpillar "20 times fuel sulfur equals oil TBN" rule was established in the early 1980's, Caterpillar prechamber (PC) engines were used for most of the test work. At that time, a difference in PC and direct injection (DI) engines was noted, with less TBN required for DI engines. With the changes which have evolved in the DI engine designs and the oil formulation changes, the new API CF-4 oils, as recommended for Caterpillar engines, will be able to handle higher sulfur fuels. The API CF-4 oils at 10 to 12 TBN would appear to be able to handle fuels with up to 1.0% sulfur.

Several factors are involved in the fuel sulfur neutralization, including oil formulation, engine design, and operating conditions. The API CF-4 oils are required for long life of the present day Caterpillar engines and will be acceptable with the higher sulfur fuels found in various worldwide locations. Some reduced oil change intervals may be required, but not to the extent that would be expected with the "20 times rule."

The preferred fuel sulfur limit for Caterpillar engines is 0.5% as defined for No. 2 diesel fuel. The customer makes a choice of engine life versus fuel costs when the fuel used is outside the established limits. To maximize engine life outside these limits requires some decisions on concessions. The selection of the oil type is a critical one. Based on the information available at this date, the API CF-4 oil is necessary to get significant life out of the engines. Older type oil formulations cause excessive piston crownland carbon formation resulting in loss of oil control. Oils with insufficient sulfur neutralization will cause engine wear-out in the ring/liner area because of corrosive wear.

Summary

For the successful operation of Caterpillar engines, the following items outline good procedures relative to crankcase oils:

1. Use oils meeting the API CF-4 performance category. (An exception is the 3600 Family of Engines which operate at lower piston temperatures and thus have different requirements.)

2. Keep the engine operating temperature (jacket water and oil temperature) above 85°C (185°F) to minimize acid formations from the fuel sulfur.

3. Use good maintenance practices to keep the engines operating correctly.

4. Use the best quality fuels possible. Higher sulfur fuels and crudes, etc. can be used, but increased engine monitoring will be required. The use of fuels other than the standard No. 2 diesel fuel will require more maintenance with higher parts and labor costs.