Fuel Oil Dilution - Mazda 6 Forums : Mazda 6 Forum / Mazda Atenza Forum
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post #1 of 16 (permalink) Old 03-16-2014, 01:42 PM Thread Starter
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Fuel Oil Dilution

Posting this as a quick heads up to 6 owners in northern climates. Checked the oil in my 2.5L gas 6 last week and the level had risen and it smelled strongly of gas. Immediately changed the oil, took a sample, and sent it to Blackstone Labs for analysis. Got the results in yesterday's mail.

The car has 2,600 miles and the oil was changed at about 1,600 so the oil only had about 800 miles on it. The car runs perfectly, no obvious problems, and gets amazing gas mileage for a full size car. The fuel dilution was at 4.8%, which is high and over the usual limit guideline of 2%. That's a problem as far as I'm concerned and I'll call Mazda tomorrow to see what they have to say about it. If you're interested in the gory details of the analysis results, I have a post up at Bob is the Oil Guy forum with the numbers.

I have read on the internet (and therefore it must be true ; ) that direct injected motors tend to have fuel dilution issues when they're run on short trips in cold temperatures and not brought fully up to temperature on a regular basis. That's true of this car, although it definitely gets an occasional freeway run where it fully gets up to temperature for a while. (3 hours of freeway time the weekend before last, for instance.) And it has been cold here in Wisconsin - we've had 34 days below zero this winter.

The net of all this is that if you've been running your 6 in a cold climate with regular short trips, you might want to check the oil, and, if it has risen and smells like gas, get an oil analysis, or at least think about getting it changed now that it's finally warming up.
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post #2 of 16 (permalink) Old 03-16-2014, 02:46 PM
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So true. I forgot to mention fuel dilution, in one of my more recent posts on getting that recommended freeway "leg stretchings" of the engine (free up the engine, to true operating temps and to attain the motor oil hot enough).

http://forum.mazda6club.com/mazda-6-...ml#post3921377

I do this 5 out of 7 days/week. 65-70%fwy/35-30% city (29-30mi of fwy, to and fro, out of a 40mi/work day drive; speeds up to 75-85mph on my 5AM to work jaunts). "Garage queen" on most weekends. I also check my oil level (includes "smell test" dip stick/gas cap comparo) "religiously" every Sat. True enough, the dip stick smells motor oil, and the gas cap..well.
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post #3 of 16 (permalink) Old 03-17-2014, 01:24 AM
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I started a thread on this months ago. Smelled fuel in my oil. Took to the dealer and concluded that it was normal. I guess that's the nature of this type of engine. It's a pain in the ass to be honest. I purposely take a longer way to work and back home . I usually add a longer trip somewhere on the weekend. It still smells like fuel but I am not going to waste hours on the highway every month just to get rid of the dilution although that's the solution. The highways around me are congested and nerve wracking. I will change my oil more often though.

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post #4 of 16 (permalink) Old 03-17-2014, 06:38 AM
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So what kind of time/distances are we talking about for this "leg stretching"? I have a 15 mile commute one way and the first 9 miles are all highway. Should this be sufficient leg stretching to help the dilution issue?

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post #5 of 16 (permalink) Old 03-17-2014, 09:07 AM
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Quote:
Originally Posted by gumby0078 View Post
So what kind of time/distances are we talking about for this "leg stretching"? I have a 15 mile commute one way and the first 9 miles are all highway. Should this be sufficient leg stretching to help the dilution issue?
I would think so, it takes the engine *maybe* 5 min to get up to temp (probably less on the highway), and the next 10 should be enough to get everything running smoothly.

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post #6 of 16 (permalink) Old 03-17-2014, 09:33 AM
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9 hwy mi/15mi, one way. That is good enough. Try to hit it at a high clip, for a few minutes. Do it regularly, I'd doubt it if you smell fuel, on your motor oil.

Give it some "Italian Tune-up".

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post #7 of 16 (permalink) Old 03-17-2014, 09:54 AM
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Welcome to direct injection. That's what's gonna happen when you pressurize fuel to 1600psi and basically mist it straight into the cylinder.

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post #8 of 16 (permalink) Old 03-17-2014, 10:26 AM Thread Starter
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cpnfantstk: saw your thread, and it's one of the reasons I sent my oil off for testing. I wanted a number to help decide how much of a problem the fuel dilution was and I'm fairly sure 4.8% is a real problem.

A buddy of mine has a Corvette that monitors oil temperature. It takes 15-20 minutes of a mostly freeway commute to get the oil fully up to temp, and I would figure that to burn off accumulated water and gas that you would need to drive for a while beyond that. I wonder if I can check oil temp off the OBD port on the 6 with my data logger - need to check into that.
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post #9 of 16 (permalink) Old 03-17-2014, 10:37 AM
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Quote:
Originally Posted by jwagner View Post
A buddy of mine has a Corvette that monitors oil temperature. It takes 15-20 minutes of a mostly freeway commute to get the oil fully up to temp, and I would figure that to burn off accumulated water and gas that you would need to drive for a while beyond that. I wonder if I can check oil temp off the OBD port on the 6 with my data logger - need to check into that.
As for the OBD port, you should be able to do that, it depends on how the sensor reads out on this car.

As for warm-up, I would imagine it does take some time for the oil to get up to temp circulating through the engine, however the Mazda6 has an accelerated warm-up feature that the corvette lacks (well depending on year).

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post #10 of 16 (permalink) Old 03-17-2014, 12:31 PM
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I agree with ExB5.

For those that care about injector health, and junk in the engine, the best medicine is to drive your car really hard at least once a week, even if it's only a 10 minute drive. Hit full throttle a few times, get the revs above 5k, get that engine hot like a self cleaning oven.

I think people that baby their cars 100% of the time: never more than half throttle, never more than 3k RPM are doing their engines a real disservice.
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