Usage:
Caterpillar Machines Powered By 3500 Diesel Engines
- SUPPLEMENT: 12/18/95
Service Magazine; May 16, 1994; Page 14; "Fuel Dilution In Engine Oil" Under"CORRECTIVE ACTIONS TAKEN TO MINIMIZE FUEL DILUTION", the information after the last bullet (*) is not correct. The correct information follows:
*If an engine application does not allow and engine idling extensively to be brought to full load and run at operating temperature, and fuel dilutions of the engine oil is present under these operating conditions, it is recommended the engine be shutdown instead of allowing it to idle. This will help reduce fuel dilution of the engine oil, reduce unneeded wear on the engine, and improve fuel economy.
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Background
This information in this article is specific to Caterpillar machines powered by 3500 Diesel Engines only. In this article, any reference to engines is a reference to the 3500 Diesel Engines in Caterpillar machines.
The 3500 Diesel Engines in Caterpillar machines have a unit injector design, which requires lubrication at the upper end of the plunger and barrel. Lubrication is needed to minimize plunger and barrel wear, as well as to minimize possible seizures. This lubrication of the plunger and barrel comes from the fuel, which must reach the upper end of the plunger and barrel; in doing so, some of the fuel leaks to the crankcase. Therefore, it is normal and expected for these engines to have some degree of fuel dilution. The degree of fuel dilution largely depends on the condition of the injectors and the application and/or loading of the engine.
It is this degree of fuel dilution that needs to be monitored and may sometimes be a high enough concern to be further investigated.
See Caterpillar's publication, "Oil and Your Engine", SEDB0640, for additional background and reference information.
How Much Fuel Dilution is "Acceptable"?
The Caterpillar limit for "excessive" fuel dilution in ALL Cat engines is 4 percent. This includes the 3500 Diesel Engines in Caterpillar machines. If the amount of fuel in the oil reaches 4 percent, the oil should be changed and the source of "excessive" fuel dilution should be found and corrected. Logically, the lower the amount of fuel dilution - the better. The Caterpillar fuel dilution limit has been derived from a combination of internal testing, actual field experience, as well as an oil viscosity blending equation. The primary concern is oil viscosity. An example of this effect is a 5 percent fuel dilution of a new nominal SAE 40 oil will reduce it's viscosity to the next lower viscosity level (equivalent of SAE 30). Caterpillar experience indicates that fuel dilution below 4 percent does not reduce engine or bearing life.
Fuel dilution may be determined by SOS testing. Caterpillar employs ASTM D3828-A "Standard Test Methods for Flash Point by Setaflash Closed Tester" for the determination of fuel dilutions of 4 percent or above.
Possible Affects Of Fuel Dilution
The primary concern with "excessive" fuel dilution is maintaining a safe oil viscosity. Excessive fuel dilution (above 4 percent) can "thin" the oil to the point that reduced oil film thickness causes an excessive wear rate or failure.
The wear rate and failure risk from excessive fuel dilution will largely depend on the level of excessive dilution and the duration of operation. Very large amounts of fuel in the oil could possibly lead to "lack of lubrication" type failures - bearing failures, premature engine wear.
With lesser levels of fuel dilution (below 4 percent), these engines should run satisfactorily to normal overhaul with no noticeable or measurable side effects. In addition, these engines are known to have very durable crankshafts and main bearings; thus making these engines less susceptible to excessive fuel dilution/lack of lubrication failures than many other engines.
SOS would be the best method for determining if excessive fuel dilution is resulting in accelerated wear.
Application Or Loading Of The Engine
In both, internal and field tests, normal, properly functioning engines can exhibit "excessive" fuel dilution from idling for long periods at a time. A test engine was run on a test stand at 1800 rpm continuously, unloaded. After 250 hours, the fuel dilution was 6 percent, and after 1000 hours, the fuel dilution was 24 percent.
Under high loads and the resulting high crankcase temperatures, some fuel is removed from the engine oil by distillation (or "burned off"). Therefore, an oil sample taken after a long, highly loaded period may indicate less fuel dilution than a sample taken after periods of idling or low loads. Also, fuel dilution may increase in the winter months as the engine oil temperatures may run cooler and/or engines idle longer to keep the engine warm. Engines running "cold" due to leaking thermostats may also exhibit an increase in fuel dilution.
Potential Sources Of Fuel Dilution
In 3500 Diesel Engines in Caterpillar machines, fuel dilution of the engine oil can result from three possible areas:
- * The first and most likely area would be the unit injector.
- * The second but less likely will be the fuel transfer pump.
- * The third and least likely cause could be a porous cylinder head.
- * The second but less likely will be the fuel transfer pump.
Leaking injector nozzles and plunger/barrel wear are the most common causes of injector leakage. As the injector wears, the clearance between the pump and barrel may grow allowing more fuel to leak into the crankcase. Also, the 6J-2419 O-Ring between the injector case and body could take a set allowing fuel to leak between the body and case joint into the crankcase. The 8J-8725 O-Rings that seal between the injector and the cylinder head can also fret and wear allowing fuel into the crankcase.
The fuel transfer pump can also cause fuel dilution if the weep hole is plugged. This condition will not allow the fuel that leaks past the 1W-4124 Lip Seal to escape and will build up in the area between this seal and 1W-4123 Oil Seal. Thus, fuel could be transferred to the oil, through the oil seal, because of the pressure build-up in this area.
Corrective Actions Taken To Minimize Fuel Dilution
Caterpillar has been actively investigating and addressing fuel dilution concerns on these engines. The following is a brief summary of some of the actions taken to minimize the fuel dilution of the oil.
A new single port metering pump and barrel design has reduced the leakage past the pump and barrel by 25 percent, while improving the seizure resistance and wear of the plunger and barrel.
The O-ring between the injector body and case has changed from a rubber to a viton material. The new 5P-8065 O-Ring replaces the former 6J-2419 O-Ring.
The fuel transfer pump lip seals are being changed to provide a better material that will reduce fuel leakage between the shaft and seal. The new seals will reduce the shaft wear at the shaft seal interface. The new 112-3596 Lip Type Seal (outer) replaces the former 1W-4123 Lip Type Seal (outer), and the new 112-3597 Lip Type Seal (inner) replaces the former 1W-4124 Lip Type Seal (inner).
In addition to specific improvements made or planned by Caterpillar, some maintenance or operational recommendations are as follows:
- * If fuel dilution exceeds 4 percent, the source of the fuel dilution must be found and repaired. The engine oil must also be changed when fuel dilution reaches 4 percent.
- * The transfer pump weep hole should be inspected periodically and cleaned if necessary to ensure it remains open.
- * An engine idling extensively should be brought to full load and run at operating temperature to help not only to "distill off" the fuel, but to also help rid the oil of some of the condensations that build up from running an engine "cold".
- * If fuel dilution is a concern, it is recommended that engines idling for more than ten minutes be shutdown. This will help reduce fuel dilution of the engine oil, reduce unneeded wear on the engine, and improve fuel economy.
- * The transfer pump weep hole should be inspected periodically and cleaned if necessary to ensure it remains open.
Trouble Shooting For Fuel Dilution
Fuel dilution may be determined by SOS testing as previously mentioned.
Some customers may use other methods to monitor fuel dilution. If fuel dilution increases significantly in a relatively short period of time, this trend should indicate a potential concern to be investigated.
Dye Check For Leaking Fuel Injectors
Tools Required for Dye Check Procedure:
NOTE: The engine must be at or near operating temperature to perform this test.
1. Add dye to fuel per dye instructions and mix well.
2. Put both fuel inlet and return lines in the 5 gallon container.
3. Start engine and run until at least 3 gallons of fuel are used. Stop engine.
4. Remove the engine valve covers.
5. Cap the fuel line and pressurize fuel system with the priming pump.
6. Use the black light to inspect all the unit injectors around the rack bar area. A leaking injector will show a definite streak (noticeable difference) of dyed fuel from the rack bar area.
NOTE: ALL injectors will seep and may show a slight amount of dye during this test. Some seepage is considered to be NORMAL, as previously explained.
NOTE: The longer the dyed fuel is in the injector, the more the seepage will appear. This test must be completed within 20 minutes from the time the system is pressurized.
7. Replace and adjust injectors leaking significantly (not just seeping).
8. Reconnect fuel lines, install valve covers and run engine to check for oil/fuel leaks.
9. Change engine oil and resample after 100 hours.