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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.
Jim
 

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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-6-3rd-generation-2013-present/298178-low-average-mpg-2.html#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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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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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?

Sent from AutoGuide.com Free App
 

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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?
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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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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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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Discussion Starter #8
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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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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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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Discussion Starter #11
Been thinking about this and want to give some more detail on how this car is driven. It takes three or four 2.5 mile round trips to work weekly. Aside from that, the car does the usual suburban driving. My wife is out doing the errands cycle right now - grocery store, cleaners, post office, etc. The car will never have a chance to cool down between stops. It also gets driven on the freeway on a regular basis, probably a couple/few times per week, but not daily. It's also our primary car for longer trips, although there's only been a couple in the few months since we bought it. I do know where the kickdown switch is and have never been accused of being a slow or timid driver.

After sifting through a lot of info on the internet I have found it's pretty much just a fact that direct injection motors leak fuel into the oil, especially with short trips in cold climates. 4.8% dilution in 800 miles is a lot of dilution and way over every suggested limit I have seen.

There are a lot of cars that are driven like ours, and I wanted to post the info on oil dilution as a heads-up to other Mazda6 owners who live in cold climates and use their cars in a similar way. If it's a concern, oil analysis is about $25 which seems pretty reasonable to know if you have an oil dilution problem which will shorten the life of your motor.

Jim
 

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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.
Bingo solar365. You hit the nail "concept", right at the head. Smart dude. :thumbup:
 

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4.8% over 800 miles is wildly out-of-spec and if allowed to continue will eventually do severe damage to bearings -- at minimum.

Either your driving pattern is really abusive in relationship to what the car is engineered for or there's something wrong with it (e.g. an injector that is not sealing and is pissing fuel into the cylinder off-time!)

Figure out which it is and put a stop to it. If you can smell gas on the dipstick you're well into the "in trouble" zone.
 

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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.
I think it is amusing this goes ignored.

Take from those of us who've been DI owners for 7-8 years now -
This is common across the board for DI engines. As was stated, high pressure, with atomized fuel vapor...yeah, it's going to happen.

And yes, those who've got shorter commutes are likely more susceptible to dilution issues. The key is to get the engine to full operating temp, and the ECU into closed loop control as quickly as possible.

It'd be nice for more of you to perform oil analysis, to collect more data, in order to establish a sort of "norm" for the S-G engines.
I'll send off a sample from my CX-5, and see how bad it is on the 2.0l.
 

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I have a Blackstone return sample pack at the ready, inside my trunk...and the 2nd OCI, 2mos from this week will be due. We'll see. I'm curious about my current MoS2 levels as well. Probably a stickie on this thread is needed..
 

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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.
Oh crap - this is definately me, trying to get best MPG's possible. I don't think of my car as a sports car - I use it as a comfortable refined commuter. Doesn't the cold start high rev process do this?
 
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