2010 yz450 gas in oil

42 replies to this topic
  • grayracer513

Posted January 16, 2012 - 12:12 PM


It's not really a fault of any kind with the rings or warm up in the case of the EFI YZF's. If you were to take a healthy carbureted four-stroke engine of almost any kind and shut down following a good day's ride, let the oil cool and take a sample, you woud find little or no fuel in the oil during an analysis. But if you took the same engine in the same state and cold started it without then letting it run for a good 20 minutes or better, the same analysis would show a significant amount of fuel contamination for the exact reasons I described above. That's just how it works.

The difference with the '10 and later YZ450 is that unlike the carb, which is manually placed in an artificially rich mode by pulling the choke, and then goes right to its warmed up engine jetting when that's turned off, the EFI unit will compensate for lower than full engine temperatures continuously all day long. When you combine this behavior with the fact that there is no thermostat in the system, and the current cold weather around much of the country where these complaints are coming from, conditions that cause the coolant temperatures to stay well under 150 degrees for the entire ride, you'll see extra gas in the oil because the engine is being run rich. If you either add a thermostat or cover one radiator, you'll bring the coolant temps up and the problem will cease.

As far as injectors drooling, Yamaha hasn't had much trouble with that, although some of the CRF's have, apparently. As to how that raw fuel would get to the crankcase in a sitting engine, it simply drains past the ring gaps and down. No more complicated than that.

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  • stroker101

Posted January 19, 2012 - 06:04 AM


you can pull the dip stick from your automoble engine and smell gasoline, normal for an internal combustion engine. same thing with a diesel engine...the oil after a awhile has a smell of diesel fuel in the oil. not neccessarily from leaking fuel injectors,
most likely caused by "blow by"

unless it is thinned out like the fuel, i (myself) wouldn't worry too much. Blackstone Labratory has analyized the oil (Rotella T / 15W-40) from my Cummins engine and recommends oil changes at 6K miles. then to send in a sample for testing. oil change intervals could be stretched out to 7.5K or longer.

(small engines, i change oil more frequently)

  • eflyguy

Posted January 21, 2012 - 05:46 AM


I was going to post about sending off samples to Blackstone. I send the oil from my street bikes and will do one for my YZ when it's next due. I didn't send the first as I don't know how long the oil had been in when I bought the bike, and when I changed it, it looked new.

They give you a full report with concentrations of metals, minerals and contaminants, as well as wear/viscosity. They also write notes, i.e.: "No serious problems to report in this sample from your Gen 1 FZ1. Universal averages show typical wear levels for this type of engine after about 2,500 miles on the oil. This oil was in use twice that long, so some extra wear would be normal, but that wasn't the case here. If we have any complaints, aluminum might be a little high compared to iron, but it's hard to be overly concerned since all other wear is low. The viscosity was in the 10W/40 range. No fuel or coolant was found and air and oil filtration were excellent. Try 6,000 miles on the next oil."

Side note - this engine has 48,000 miles on it. I know a guy right now rebuilding one with similar miles to replace worn exhaust valve guides and seals that were responsible for oil consumption between changes. He's posted pics, the engine looks like new internally - those motors hold up. I know a girl about to roll over 200,000miles on hers.

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