Successful Farming Engine Man Ray Bohacz has engine grease and field dirt under his fingernails from a life spent repairing vehicles and running a farm. When he's not busy in the shop, he's working on maintenance articles and videos for Successful Farming magazine and answering questions from readers. The following is a letter Bohacz received from Ryan Damery:

I have a Freightliner with just 282,000 original miles. It runs with a model 3406 Caterpillar diesel that was overhauled three years ago. I just bought the truck from my father, but I suspect that the overhaul was required at such low miles because when he bought it, the dealer sold the truck with an air cleaner that was not fitting properly. A year later he checked the air cleaner to find that it was not fitting tight and had been sucking dust for a year. A few years ago we started noticing a lack of power about halfway through the year and only had put about 1,000 miles on the truck per year. The oil level was high at that point and it smelled of diesel. I have searched the Internet regarding the problem and it seems that this particular Caterpillar engine has an injector seal that can leak. When that seal leaks, diesel gets into the oil. Do you know anything about this problem?

Based on your finding of diesel in your engine's oil, your theory of the problem being an injector/nozzle seal or cup is probably correct. But you, or the shop that will work on the engine, needs to discover "the smoking gun." Some engines may have a crack in their cylinder head which could cause this same problem. But I do not think it is the case with your Caterpillar engine. 

Please keep in mind that diesel fuel in the crankcase drastically impacts the oil's lubricity and creates excessive wear in all parts and the turbo bearing. I would take an oil sample with the contaminated oil and send it to a lab. They will tell you what you already know, that there is fuel in the oil. But what you need to determine is if there are any high levels of any engine bearing material in the oil. That will allow you to judge if there is any real damage that has occurred to the engine. Based on the report, I would then go after the oil dilution problem. Even if the engine has seen some excessive wear from the diluted oil in the past, that Cat engine will probably serve you well for many years with the low use you give it . . . that is, once you stop the diesel from getting into the oil. Thus, do not get too upset if the oil analysis looks a little on the bad side. It is better to know a general idea of the engine's health before you do anything.

Do you have a maintenance question? Email Ray Bohacz at SFEngineman@agriculture.com.

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