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Old 10-13-2018, 05:34 PM
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Vlad Vlad is offline
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Location: Utah
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Question Oil system flush how to?

Is there a method to flush engine oil system? I rinse the sump occasionally with couple quarts of gas and I flushed out oil cooler couple times. How could I flush the whole system? What liquid/solvent/oil to use?
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Old 10-13-2018, 10:23 PM
lr172 lr172 is offline
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Location: Schaumburg, IL
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I would discourage any attempt to flush out your oil system. Manually cleaning the sludge or debris out of the pan is fine and that is where most sludge and debris ends up. Running gas through it won't do much, unless you give it a long soak time. Usually some manual effort is required to get it out. However, any sludge, debris or varnish that you loosen in the oil galleries or tributaries runs a high risk of getting lodged in smaller downstream clearances, such as lifters, pushrods, prop governors, etc. and creating problems that did otherwise exist.

This is very common in automatic transmissions (much smaller passages). Owner neglects trans for 90,000 miles then tries a flush with a lot of detergent. This breaks everything up and is free to float around and clog circuits. Next step is a complete rebuilt to get it to shift properly again.

The general wisdom is that if the build up is not causing problems, leave it alone. Trying to remove it is high risk, low reward.

Do you have reason to believe there are builds up in your system that are creating problematic restrictions? If you are infinately curious, you can remove the two clean out plugs in the main gallery and inspect it. However, resist the urge to run a brush down through it. Most of what comes off will go down the capillaries.

Additives, such as MMO, will typically only thin out sludge and do so very slowly. They also don't typically break off hard solids. For these reasons, they generally do no harm and will help with heavy sludge buildups. Any sludge dissolved will typically end up again as sludge in the bottom of the oil pan where it does no harm.

The best way to prevent sludge is frequent oil changes. Sludge generally forms when the oil's capacity to keep debris in suspension is exceeded(i.e. becomes fully saturated) and it settles out via gravity, though it can stick to cavities the oil is flowing through. This exclude the Gelatenacious gunk that forms from excess moisture and limited full temp runs.

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Last edited by lr172 : 10-13-2018 at 10:49 PM.
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Old 10-14-2018, 05:19 AM
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turbo turbo is offline
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Vman, as much as we fly I dought there is much sludge in our engines. Carry on. How many hours on that lyc anyways. A rebuild would definitely get the sludge out though.
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Old 10-14-2018, 05:33 AM
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Default Oils

There are some automotive oils that are really good at cleaning due to the detergent package. Maybe after draining your regular aviation oil, put some rotella diesel oil 20w50 and fly it for a couple of hours or till it starts to change color and drain it and change filter. This oil has the right viscosity for our flat tappets engines. I?ve heard some folks in the know say a rotella run engine is a very clean engine at overhaul. I?d avoid the full synthetic though. Stick with the conventional stuff.

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Old 10-14-2018, 06:41 AM
rocketman1988 rocketman1988 is offline
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Default be careful

From experience, be VERY careful with automotive type oils. There additive packages may or MAY NOT work like you think. Years ago, an automotive type oil was used in a C-320. Upon shutdown, the props feathered...definitely not normal. Long story short, the additive package in the oil did not play well with something in the engine, heat, 100LL, or ???.

The oil turn to a pudding consistency...NOT GOOD...

We never found out WHAT specifically caused the issue but that oil was the culprit.
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Old 10-14-2018, 06:54 AM
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rocketbob rocketbob is offline
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Vlad in Soviet Russia they flushed with cheap Vodka.

With as much as you fly, no need to flush anything. I like to use MMO which does a good job at dissolving deposits. But if you insist on flushing, you can use the main ingredient in MMO which is mineral spirits.

I once saw 1/4" of sludge in the sump of a 540.

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Old 10-14-2018, 06:54 AM
BillL BillL is offline
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Location: Central IL
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Hmmm, I'd have to agree with Larry on this one. I would do anything drastic. More frequent oil changes will do more and safely. The most radical approach might be a new oil change with one quart of 100ll mixed pretty well before pouring it in, start and run for an hour then drain hot and put fresh oil in there. The 100LL should have all been pushed out the breather by then, but anything dissolved or suspended would still be in the oil. Still it has risks, but not too much in this case. You could cut open and inspect the filter out of curiosity, but suspect nothing would be found there. Easier just to drain the oil and replenish.

Oil additives generally last pretty well, and stuff in suspension peaks in about (typically) midway though the recommended oil change period. (That was 25-50 hours on a diesel) If I wanted to do a cleaning, then use my standard oils with a 25 hr change for the next 2-3 changes and then back to normal.

If you had a history of oil analyses, then an analysis of the 1 hour could be compared to see if it collected anything. An experiment, really.

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Old 10-14-2018, 02:06 PM
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Jesse Jesse is offline
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Location: X35 - Ocala, FL
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I once found a sump on an O-360 that had 1/4+? of sludge in it. The guy would always call his mechanic to come do the oil change, so it was always changed cold. I once changed it and by the time he got to his hangar it was black. I ALWAYS change the oil after a flight so the crud that has settled out gets suspended and drains with the oil.

I always change the oil at 25-hour intervals and filter every other change. Oil analysis every time.
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