changing oil hot or cold???

Hi All,

I have always changed engine oil on my RV-8 after flight so the engine is hot. Yesterday I was talking with an inspector from Chilean FAA and he told me why you do that, is there any lycoming SB, SI or recommendation that said the engine should be hot for changing oil?, so I said yes, then he told me show me a document. I have been searching and I can find any recommendation about it.

Please help

In the summer, I'll just drain the oil without running the engine first. If the outside air temps are warm enough (80? F / 27? C) the oil drains just fine without any addition coaxing.

In the winter, in Minnesota, doing the same thing would result in the oil taking days to drain so during those times I'll fly for an hour or so then drain the oil afterwards while it's still nice and hot.

I'm not aware or any Lycoming, or FAA document for that matter, that recommends running the engine prior to an oil change to warm up the oil. Lycoming SB 480E, Oil and Filter Change and Cleaning, only states when and what to inspect, not how to do it. Nor does it say to do so in my Lycoming operators or maintenance manual (to be fair I only have the manuals for a 540).

So why do a lot of us do it that way? It boils down to sort of a best practice for 2 reasons:

1. Warm oil drains faster than cold oil
2. More importantly, IMO, running the engine and warming the oil will maximize suspension of contaminates in the oil that we want to remove from the engine

Is it mandatory or actually necessary? In my opinion, nope. But I will continue to do that way. YMMV....

Better drainage

Some feel that warm oil will drain more completely. However we still have about a quart in the oil cooler that never drains. So at oil change we never get all the old oil out

Gary Specketer

Auburntsts said:

So why do a lot of us do it that way? It boils down to sort of a best practice for 2 reasons:
1. Warm oil drains faster than cold oil
2. More importantly, IMO, running the engine and warming the oil will maximize suspension of contaminates in the oil that we want to remove from the engine
Is it mandatory or actually necessary? In my opinion, nope. But I will continue to do that way. YMMV....

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THIS is the primary reason to drain the oil when it is hot.

yes, it's the only way to get the sludge out. You are leaving a bunch of **** in the engine if you drain it cold. It's kinda like mud and it just collects there in the corners.

Auburntsts said:

More importantly, IMO, running the engine and warming the oil will maximize suspension of contaminates in the oil that we want to remove from the engine

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I have a filter on the engine that does this for me when the engine is running. Not sure how much difference draining the oil when warm would actually make. Haven't found any significant amount of sludge in ~650 hours either, so who knows?

I just changed oil yesterday after running the engine first. When I removed the filter, it was full of oil and made a bit of a mess. Does most of that oil drain out of the filter if the engine is not run prior to oil change? John

jpowell13 said:

I just changed oil yesterday after running the engine first. When I removed the filter, it was full of oil and made a bit of a mess. Does most of that oil drain out of the filter if the engine is not run prior to oil change? John

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No. Some, maybe, but there will always still be quite a bit in the filter unless you have an angled oil filter adapter.

warm oil

It takes forever for cold oil to drain out. PERIOD.

jpowell13 said:

I just changed oil yesterday after running the engine first. When I removed the filter, it was full of oil and made a bit of a mess. Does most of that oil drain out of the filter if the engine is not run prior to oil change? John

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If all that oil drained back into the engine on shut-down, every time you started the engine it would have to fill the filter before supplying oil to the engine. You wouldn't want that!

Mel said:

If all that oil drained back into the engine on shut-down...

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Funny you should mention that. I just learned yesterday that Tempest oil filters have an anti-drainback valve (like a flapper valve) to keep that from happening. I assume other brands have something similar. Oil Filter ADB Valves

The ADB valve?s job is to trap oil in the passages leading from the sump, through the pump, and to the filter. As long as the pump stays full of oil,
even hot thin oil, it will re-establish oil pressure almost instantly after the engine is started.

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I drain mine cold in the Summer. I don't like working around a hot engine. I have noticed slightly less oil in the filter when draining cold and I make less of a mess. Besides, my oil is still clean at 50 hrs and I wonder why I am doing this.

On cars, boats , motorcycles, lawnmower and my airplanes i always drain it hot or at least very warm for the reasons mel elaborated. Its pretty amazing that you can check the dipstick and it looks pretty good after it has set for a week or so but when you drain the oil out its pretty ugly looking. not near as clean as the dipstick showed. If at all possible I always fly or run up the plane or use the engine for the other vehicles and then drain the oil. On my plane while things cool down and the oil is draining it is a perfect excuse to do a quick compression and timing check, clean out the air/oil separator suction tube in the exhaust, mouse milk exhaust joints and just look everything over real good. I takes me just shy of four hours to do the whole thing, cowl off to cowl on and I don't rush things. I generally don't pull the oil screen until annual time unless I find something that doesn't look right in the filter when I cut it.

Once I just pulled the cowl when the oil was cold, drained the oil, changed the filter and put the cowl back on. The plane flew just fine for the entire trip - It was amazing. I was nervous the whole time tho thinking about what i should have checked.

And about that sludge thing - just pull the oil pan on an engine that has 1000 hours or more with regular oil changes. You will be amazed the amount of **** that is in there especially the amount grey lead deposits.

warm vs cold sample

Taking a warm oil sample is recommended for oil analysis... to be taken within 30 minutes of engine shutdown.

I cut the filter after every oil change but do not send for oil analysis. What is my risk?

Flying to warm up the oil prior to an oil change is like having dessert before dinner!. Why not? Also you need to do an engine run and take it for a post oil change operational check flight. Now it's like having dessert twice!

maybe two check flights. opening my kimono, I changed my oil a week ago and did a check flight and all was good. upon the second flight with a passenger my top cowl pushed open an inch. darn it, I forgot to install the aft top cowl pins. back to the airport, install pins and continue the flight.

Steve Melton said:

I cut the filter after every oil change but do not send for oil analysis. What is my risk?

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An oil analysis can show trends that allow you to identify potential parts failure before they occur. Kind of like cheap insurance. For my money, it's worth the $25 it costs (Blackstone) so I can have the data. However, it is not a panacea, just another tool in the kit, so to speak.

Steve Melton said:

I cut the filter after every oil change but do not send for oil analysis. What is my risk?

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Oil analysis is an early warning system which may alert you to potential problems. I think it's cheap insurance - about $15 per analysis. I use Lab One Aviation in Phoenix and have been pleased with them. The owner even spent about 20 minutes on the phone with me one time answering a question on "high silicon". I send in each sample via USPS and they email the results back as a .pdf. They also keep a history of my engine.

ChiefPilot said:

I have a filter on the engine that does this for me when the engine is running. Not sure how much difference draining the oil when warm would actually make. Haven't found any significant amount of sludge in ~650 hours either, so who knows?

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There's a lot of contaminates in used engine oil that the filter does not catch; it's not just particulate contamination to be concerned with.

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I think I remember the hot oil change being taught as a "best practice" in A&P school, and not a requirement.

The Sikorsky CH-53E, S-76, and S-92 maintenance manuals, the Bell 412 maint. manual, the P&WC PW210S and PT6T maint. manuals, and the GE CT7 maint. manual (I think Agusta, Eurocopter, and MD are similar, but it's been a while since I worked on those), all require a hot oil change as part of the required maintenance after a suspected or confirmed case of oil contamination, to include popped filter buttons and chip lights with chips found. They do not direct a hot oil change for scheduled oil changes; in fact, I've never done a hot oil change on any helicopter as part of scheduled maintenance - I've caught them still-warm a couple times, but never hot. At their formal engine school (Arriel 2S1/2S2), Turbomeca recommends a hot oil change for all oil changes, but only requires it for suspected/confirmed contamination.

Granted, these are turbine engines and helicopter gearboxes, so the info isn't a direct transfer to the RV/GA world, but it does help illustrate the thought processes of OEMs.

FWIW, I do hot oil changes in my vehicles, and I would do hot oil changes if I were an RV owner/maintainer. It's what I was taught as a kid and a young adult, and I personally believe it's a valid technique.