What are the causes for diesel fuel in engine oil? My friends Perkins T6.354 is getting fuel in the oil.They thought it was faulty injectors but after rebuilding the fuel is still present in the oil after test running. What other possibilities for fuel getting into oil should they investigate ?
On the 6.354 it is rarely the injectors. You'd see a huge slick on the water and tons of white smoke before enough would get in the oil that way to flag an oil sample or "make oil" within a normal interval. I'm talking more than the expected white smoke and small slick the turbos versions of that engine like to produce at the dock. The problem would have likely gotten fixed for other reasons before fouling the oil.
Most of the time on the 6.354 it is a bad mechanical lifter pump. When the membrane gets even a little perforated, a ton of fuel can get in the oil. This is a relatively fast, easy, inexpensive, very available fix.
Almost all of the rest of the time it is the injector pump, not the injectors. When the shaft seal (maybe there are two, I dont remember without looking) fails, tons of fuel can quickly get in to the oil. A rebuilder can check this on the bench, but will usually charge for a full rebuild if repair is needed.
The usual advice is to replace the lifter pump, change the oil and filter, and test again almost immediately, after just enough run time to get to temperature and everything mixed well, and then test again after a small several hours of use.
It is important to sample mmediately so there is a baseline to compare with the next sample (the one taken after some real use). Without that, one can easily be confused because not all the old oil, and with it the old contaminating fuel, gets changed during an oil change.
If the two samples show the same level of fuel dilution, that just means that the oil needs to be changed again until the old contamination is sufficiently diluted out (oil changes dont get all of the old oil out, and that engine can be particularly hard, depeneing upon how you go about it, given the shape of the pan). But if the 2nd sample is notably higher than the 1st sample, the problem is ongoing and the lifter didn't fix it, so attention should be turned to the injector pump.
After swapping the lifter, take a look at the membrane on the old one. A lot of times tou'll see the failure and, therefore, be confident you fixed it. If not, hang onto it as a spare, at least until you see what the oil samples suggest.
Obviously, even after you think you've fixed the problem, sample frequently for a bit to be sure. Some failures may only occur under load, when hot, episodcially, etc.
If you haven't done oil samples before, just get a pump and a kit from Amazon. They are both inexpensive. The one time use kit is usually ~$20 and includes the cost of the lab analysis. Just send it in. Drawing the sample is just warming up the engines a bit, then shutting down, threading a tube into the oil pan (without scraping up any sludge at the very bottom), and using the hand pump to draw a sample into the sample container. The kit usually comes with both the one-time-use tube and container (but check, because some only contain the container, which is a bummer for most).
Of course I have many questions...
How do you know there is fuel dilution? How much? And over how many hours of engine run time?
And, how is the engine running, otherwise? Is there a ton of white fuel smoke? A big slick on the water? Dirty underway? A ton of blowby?
And, how has the boat been used? Are those hours idling at the dock in short stints? Or underway largely at cruise?
A slow rate of dilution in a boat with a lot of blowby might just be an aging engine.
A slow raye of dilution in an engine running dirty could just be aging or badly needing maintenance (air filter if equipped, valve timing, fuel filters, etc).
An engine idling a lot, e.g. rarely used for real but often idled at the dock, can diluted a lot faster than an engine running at cruise because it spends more time cool.and running dirty.
In general, the slower the rate of dilution and the more obvious the other performance problems, the more likely it is to be age, maintance, or injector or injector pump performance.
The better the engine is running otherwise and the faster the rate of dilution, the more likely it is to be a seal, most commonly the lifter membrane or injector pump shaft seal.
Snce most don't notice really slow dilution or just dismiss it with the other signs of the engine's general condition, the problem is most commonly the lifter pump (membrane) followed by the injector pump (shaft seal).
