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Condensation in oil filler cap


Old 12-05-2011, 12:16 PM
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Default Condensation in oil filler cap

This is probably nothing but I thought I'd check it out here. I changed my oil yesterday (been running synthetic for the last 20k miles or so). When I pulled the oil filler cap off, several droplets of water fell out of it and I turned it over and the underside was somewhat wet. When I drained the oil, it didn't look milky at all and the oil actually still looked pretty good. Is this common and just a result of some condensation given that it's the time of year where it gets pretty cold at night but temps during the day are still often in the 60's or low 70's? Or do I have water getting in my oil somehow?
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Old 12-05-2011, 12:58 PM
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That is not a good thing. Hopefully, it's just condensation (likely is). How far is your commute? That is often the result of the engine not getting hot enough to burn off the condensation that occurs. Common issue in colder weather.
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Old 12-05-2011, 02:04 PM
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Sounds like condensation from large temp fluctuations. If the night temps are prett cold, the oil is cold at daylight, and since oil is pretty thick and blocked from the sun, the outside ambient temp starts raising the oil pan temperature all while the oil is cold. This creates condensation on the oil pan.
Moisture under the cap can be from same thing, along with short duration trips like to the store and back. You can have a perfectly dry internal engine that drips water off the filler cap like yours did when temps change. It's called Dewpoint and creates moisture.
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Old 12-05-2011, 03:03 PM
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It's been happening on my trucks and freinds trucks for years and thousands of miles. I even asked the dealer who said they too see it all the time. Not something i would worry about. It's caused by what Dirty describes. My wifes Dodge Intrepid has the issue as well.
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Old 12-05-2011, 03:27 PM
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Makes sense guys and thanks. I work from home and there are days my truck never even gets started and then days where I drive it to run errands. I drive it long enough to get to full temp but probably not long enough to get rid of all the moisture. That, along with the fact that it is that time of year. 30's and low 40's at night and up to low 70's in the day. I do take the occasional road trip that would probably more than get rid of the condensation.
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Old 12-05-2011, 03:30 PM
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It's absolutely nothing to worry about as long as the oil has no signs of contamination when you drain it.

Lot of contributing factors cause it, weather changes and especially driving a lot of short trips where the engine oil does not sustain high temperature enough to burn off the condensation that naturally form...
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Old 12-05-2011, 05:10 PM
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This sort of thing is seen in aircraft engines also. It is said that auto engines wear out while aircraft engines tend to rust out. This is because auto engines tend to be run more frequently while aircraft may sit for weeks to months between flights. I have seen completely rust coated cylinder walls after an engine sitting 1 year.

When the temperature drops to the dewpoint, fog will form. In the engine that will be seen as your condensation. Yes, it needs to be run until it is hot to hone the cylinder walls and evaporate the condensation.
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Old 12-06-2011, 12:23 AM
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Mine is dripping wet all the time. I dont like it, but is has not caused any issues. I park my truck in a heated garage in the winter, so it's constantly going from warm to cold... I wipe it out with paper towel when I think of it...
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Old 12-06-2011, 07:11 PM
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Just noticed this in my truck tonight when adding 1/4qt. Had pooling in the cap even after I turned it upside down. My commute is 1.2 miles 3-4 days/week. Occasionally I do have a 500 mile road trip or errands of course.

Anyone reckon the passive breather used in my CAI setup would create more condensation than the factory airbox with an actual breather under negative pressure? I have thought of sticking the factory box in till March. This is mid Ohio, USDA zones 5-6.
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Old 12-07-2011, 12:23 AM
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when we run a standby gas engined generator on a test cycle every month, we put it under full load for thirty minutes at operating temperature for just this reason.
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