Letting Oil Drain Overnight

[garageman402]

I like to let the oil drain overnight (or all day) or longer. I know there will always be oil left in the motor, but at least that much more is out. My high school friend’s dad had a gas station & he let his car drain all day, said the oil seemed to stay clean longer.

I have now been told that allows the pump to cavitate resulting in dry startup. I disagree, as soon as you take the filter off, air is allowed in the system so the pump will fully drain. I pre fill the filter & “flood clear” to prime the system before starting it anyway.

Is there any fact here? Or just another old mechanic’s tale?

 

[2010Civic]

You could change the oil 50 miles sooner and probably achieve the same effect.

 

[SureshR]

Old mechanic’s tale. Whatever you do there’s going to be some old oil circulating around the engine. So if you’re concerned about the oil staying clean just change it earlier.

This video was posted in another thread - just buy the cheapest oil that matches the spec your car needs and change it every 3k miles or six months whichever comes first.

Assuming city driving and typical Japanese traffic I guess but I’ve seen similar bumper to bumper traffic in NYC and Boston.

 

[vavavroom]

The last drop to fall should be the most contaminated. Once the flow from the drain becomes a trickle I let it drain for another 30 minutes.

 

[camrydriver111]

The longer you drain the better.

Whenever someone else does my oil changes the oil is darker on the dip stick afterwards. They replace the drain plug too early.

I also open the fill cap when I let the oil drain.

 

[Owen Lucas]

I like to let the oil drain overnight (or all day) or longer. I know there will always be oil left in the motor, but at least that much more is out. My high school friend’s dad had a gas station & he let his car drain all day, said the oil seemed to stay clean longer.

I made a video on this topic. Basically draining for an extra 12 hours gets you a miniscule amount of extra oil out, but there is no harm in doing it of course.

In the video I drain the oil for 12 hours on a 2005 Scion tC with the 2.4l 2AZ-fe 4 cyl engine.

1 hour is the sweet spot for this engine (and probably most others as well) where the most extra oil comes out. The remaining 11 hours only yields an extra 50 milliliters where as you get the most drainage in the 1st hour on a hot oil drain.

 

[vavavroom]

I also open the fill cap when I let the oil drain.

Also, pull the dipstick at least so it's loose. The tube is sealed and may not drain properly without equalized pressure.

 

[02zx9r rev2]

I let mine drain for at least a week. Seriously….why not figure out a way to flip the car over and get every last drop out

 

[Wingo]

I don't drain overnight, I don't have that kind of patience. Though I do pull the plug and filter, then clean the car out.
Vacuum, treat the plastics and leather, hang a new little tree new car scent, etc. Then I complete the oil change. It's what my dad taught me to do except he liked spice and vanillaroma little trees, yuck, not a fan. As long as you have the time you can kill two birds with one stone.

 

[RazorsEdge]

I'll let it drain at least an hour or so. I have let it drain overnight as well. All depends on what is going on.

 

[garageman402]

This video was posted in another thread - just buy the cheapest oil that matches the spec your car needs and change it every 3k miles or six months whichever comes first.

Assuming city driving and typical Japanese traffic I guess but I’ve seen similar bumper to bumper traffic in NYC and Boston.

Ya, I tried that too. Decided better oil will give better protection.

The question is will draining the oil 12+ hours increase oil pump cavitation? My thought is it makes no difference once air is allowed to reach the pump.

 

[Gyro Gearloose]

Waiting hours and hours or overnight also gives the oil on the bearings and lifters the maximum time to drain out so they have the minimum amount of oil left on them for that 5-6 seconds of zero oil pressure after an oil change.

As a general rule, I'll take old oil over no oil every time.

 

[garageman402]

I don't drain overnight, I don't have that kind of patience. Though I do pull the plug and filter, then clean the car out.
Vacuum, treat the plastics and leather, hang a new little tree new car scent, etc. Then I complete the oil change. It's what my dad taught me to do except he liked spice and vanillaroma little trees, yuck, not a fan. As long as you have the time you can kill two birds with one stone.

I don’t sit & wait for it to drain, I’ll leave it & come back later.

 

[SureshR]

Thanks


Ya, I tried that too. Decided better oil will give better protection.

The question is will draining the oil 12+ hours increase oil pump cavitation? My thought is it makes no difference once air is allowed to reach the pump.

A fully drained oil pump is what Ford specifically asks to avoid for my car (Endeavour aka Ranger in a 7 seater SUV version, 3.2 diesel). Refilling just doesn't ensure positive suction in the oil pump once you refill, so it still runs dry and cavitates.

 

[garageman402]

Waiting hours and hours or overnight also gives the oil on the bearings and lifters the maximum time to drain out so they have the minimum amount of oil left on them for that 5-6 seconds of zero oil pressure after an oil change.

In general I'll take old oil over no oil every time.

Oil will drain out of the bearings & lifters anyway, whether the pan is full or empty. I “flood clear” crank it a few times to prime it.

 

[02zx9r rev2]

In all seriousness, when it slows down to a slow drip, plug reinstalled ( or Valvomax unscrewed in my case) and refill and go on about life.

Never had a problem or concern about the little bit of residual oil left

 

[garageman402]

A fully drained oil pump is what Ford specifically asks to avoid for my car (Endeavour aka Ranger in a 7 seater SUV version, 3.2 diesel). Refilling just doesn't ensure positive suction in the oil pump once you refill, so it still runs dry and cavitates.

So how long does it take for the Endeavour oil pump to drain out? Wouldn’t removing the filter allow air in to allow the pump to drain?

 

[billt460]

I have 3 vehicles I do one after the other. So for me it would make oil changes a 3 day affair. So I'm not going to mess with that. With that said, I believe the longer you allow it to drain the better.

I drain hot, and allow it to drain until the drain is reduced to a single drip. That can take a while in my Jeep.... For both the pan, and the filter. For my truck, (Ford), and my Toyota, it only takes a few minutes.

I don't think allowing it to drain overnight is going to do anything as far as causing a, "dry start". The engine either has oil or it doesn't. The oil pump is going to start pumping the instant the engine is started, if the pan is filled to proper capacity.

You will do more good by pre filling your oil filter, (and you will get oil pressure notably faster), than you will "harm" anything by draining overnight.

 

[vavavroom]

I let mine drain for at least a week. Seriously….why not figure out a way to flip the car over and get every last drop out

You could remove the oil retention valves in the head(s). Then you won't have to turn the car over.

 

[02zx9r rev2]

You could remove the oil retention valves in the head(s). Then you won't have to turn the car over.

Will have to try that. Thanks for the suggestion