How important is it to drain oil hot?

[blupupher]

If your only draining out 5 qts of a 6 qt system, something is wrong.

My car holds 4 qts. When I change my oil, the dip stick reads full, I drain the oil, R/R the filter, and add the 4 qts that my car holds. When I am done, I am back at the same full mark I started at. It has been the same with all the vehcles I have had, from the current 4 qts to 7 qts. I just don't see where this "extra" oil is at.

 

[1sttruck]

The amount of oil you need for a dry engine, like after a rebuild, is always higher than the oil change qty. Oil is kind of thick, there is lots of surface area, and places for small quatities to collect.

 

[got boost?]

quote:

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Originally posted by Drew99GT:

quote:

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Originally posted by got boost?:
the most important thing is that when the oil is changed hot, there is still a layer of oil on the engine parts so the startup doesn't do as much damage. it is best to get the change and restart the engine in 1/2 hour or so.

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Hmmmmmmm, wouldn't it be just the same as starting an engine stone cold the 1st time each day?

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Okay, we all should know that cold starts cause much engine wear. So, when you turn the car off the oil drains from cylinder walls and down from the valve train, BUT the oil system remains full of oil (assuming proper function).

after an oil change, the oil film is gone from the engine just the same, but in addition, the oil system is empty, the amount of time necessary to fill the system is significant when considering a cold start.

oil poured into the oil fill coats nothing other than the drain passages on the head.

[ July 13, 2005, 12:15 AM: Message edited by: got boost? ]

 

[Bryanccfshr]

I like to have a warmed up motor and allow it to drain until it won't drain anymore. One of my vehicles, the Mitsubishi has about a 1/8" wier that holds some old oil in hte oil pan. I have found that pouring about half a quart of fresh(and cheap) oilthrough the engine will get all the nasty stuff from behind that wier and allow the drain oil to go from dark to translucent to new oil clear.

I look forward to changing the oil on my Taco again(Only six more months!!), mostly so I can install the Fram sure drain. And play with it as a sampling device.

 

[TallPaul]

I lost oil pump prime once and had to pull the filter and backfill the pump outlet with an oil squirter. There is a FAQ on it in the Filter Council FAQs or the Hastings Filters site, IIRC.

 

[thrace]

I often change oil when the vehicle is cold. Just for safety. Much less chance of getting burned on a hot exhaust or burned by hot oil. It never freezes where I live. It must be better to change the oil when it is time even when cold than wait for the perfect conditions. And leaving the car to drain for hours, that could increase the chance of someone driving the car before the oil goes back in.

 

[Patman]

quote:

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Originally posted by thrace:
I often change oil when the vehicle is cold. Just for safety. Much less chance of getting burned on a hot exhaust or burned by hot oil. It never freezes where I live. It must be better to change the oil when it is time even when cold than wait for the perfect conditions. And leaving the car to drain for hours, that could increase the chance of someone driving the car before the oil goes back in.

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Not if the car is up on ramps though. You won't forget to add oil if the hood is open and the front wheels are up in the air the entire time it's draining.

 

[surfstar]

i drain it hot-warm. usually hot and the oil isn't the problem, its the da*n hot filter. also to ensure complete draining, i jack the car up a decent ways, then lower and jack back up to ensure full drainage of oil pan (plug is low at the rear). when it stops draining at one height, i jack it up a little and a steady *dirty* stream will come out again.

 

[motorguy222]

I think that it is better to change the oil at operating temp or close to it.

Oil not only suspends particles but it may also have harmful acids and byproducts of combustion in it.

Getting the oil at op. temp should help in getting these 'products' mixed well into the oil so that it can be drained out.

One of the main goals of oil is to keep bad things in suspension while the engine is running.

Hot oil also should be better at removing any particles that may settle in the pan.

While there may not be a large amount of particles that have settled,even a small amount can cause problems.

If the oil is changed cold at every change,the particles could add up over time.

It may not be a sludge bucket but every bit of sediment that can be removed needs to be.

This sediment would be smaller than the pump screen would stop and may be smaller than a filter may stop,depending on the filter.

It also may cause a filter to go into by-pass mode sooner,more often or for longer periods of time.

 

[Starbreaker666]

It comes down to pain threshold mostly... I darin Hottish warm... Not hot enough to burn the skin and only has a little bite to it.. Doesn't bother me a bit. I usually drive to the store buy said OCI supplies drive it home up on ramps and drain.... Toughen up boys! HEHEHEH....=)

 

[obbop]

Still pondering.......................

 

[Shannow]

As to mixing, how much oil does an oil pump move ?

a couple of gallons a minute ?

The junk should be well and truly mixed after 5 or 6 minutes.

 

[Frank D]

Damm, I never knew how much thought went into an oil change.

 

[obbop]

But, conversely, pondering the imponderables, visualizing the uninvisuable, an analogy is propelled to the forefront:

Two containers holding oil. One hot, the udder cold.

Drop a pearl into the containers. For drama select a rare expensive pearl. I betcha' the pearl reaches bottom first in the hot oil.

So, what does that prove?

Nuthin', of course!!!!!

But, this is a moment for conjecture. Warm an engine. Do what you typically do to commence an oil change. Open the draining orifice. Is it possible that some unwanted contaminants will have settled out of the warm or hot oil? Will the "friction factor" between solid contaminants and internal engine surface overcome the "tug" created by the oil headed for its own little "Niagra Falls" as it departs through the circular departure point commonly known as the oil drain hole?

Visualize the same scenario with cold oil. The solids, even if they are not suspended within the oil, are subjected to a greater "tug" as the oil responds to gravity's relentless call to descend to the exact center of the Earth, stopping only due to materials preventing that lengthy trip.

As previousy mentioned, cold oil will take longer to drain but this thread was not started to discuss the length of time needed to complete an oil change. This is not corporate America where seconds saved so as to maximize profitablility is held in higher regard than performing a task properly.

NAY!!!!!!!!!!!! Nay, I say. Neigh, sayeth the equine.

So it may take longer for cold oil to drain. Big whoop de doo dah doo. Go read a book for ahile. Beat the kids. Beat the wife. Pet the dog. Get a 2nd job. Brush thine teeth. Anything. Doesn't matter. Take a few more minutes to allow the cold oil to glub glub glub as it performs an action somewhat akin to the Titanic, the Lusitania, the Edmund Fitzgerald. Well, kinda' like that. In a way. Sorta. Glub.

Ponder, I do. Not asserting that draining cold is better than draining hot. Just tossing into the realm possibilities. Refusing to refer to knee-jerk reactionism. For decades I heard that draining hot was best. How many people have actually performed scientific research to determine the superior draining method? Who has spent time considering the various ins-and-outs of glubbing oil and what determines that the maximum amount of unwanted particles follow that oil out that little hole strategically placed at the hoped-for low point of an engine.

Glub.

 

[motorguy222]

Think about it.

Is something going to mix better hot or cold?

Some of the stuff in an engine is probably not going to get truly mixed into the oil until it gets to around operating temp.

Think about trying to mix two cold products.

Many times it doesnt work very well.

Now,mix the same two products while warm/hot,they should mix much better and much quicker.

Hot oil,in my opinion,is going to get more of the bad stuff out of an engine than cold oil will.

 

[mjo]

What do you think? Thread a solenoid into the oil pan bolt. Wire up a circuit and install a round red push button on the center counsle. A little plumbing attached to the pressure sender and a 5L metal container with new motor oil. Now, whenever the ODO hits EXACTLY 3,000.000 miles push the red button. Whoosh, the old oil pours out, smoothering the obnoxious tailgater making him swerve uncontrollably into the ditch. After a 3 second delay the solenoid closes, another solenoid opens and pumps oil into the engine. End of oil change!

 

[Patman]

Drain the oil hot, and wear gloves if you're worried about getting burned. Or get a Fumoto or Sure Drain system in order to lessen the risk of getting burning hot oil on your hands when draining.

 

[TallPaul]

quote:

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Originally posted by mjo:
What do you think? Thread a solenoid into the oil pan bolt. Wire up a circuit and install a round red push button on the center counsle. A little plumbing attached to the pressure sender and a 5L metal container with new motor oil. Now, whenever the ODO hits EXACTLY 3,000.000 miles push the red button. Whoosh, the old oil pours out, smoothering the obnoxious tailgater making him swerve uncontrollably into the ditch. After a 3 second delay the solenoid closes, another solenoid opens and pumps oil into the engine. End of oil change!

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Great idea.

Your device would solve the cold startup problem. What if the oil drains to a holding tank and we have two tanks, one with 0w10 and the other with 10w30. In winter we start up on the 0w10 and once the engine begins to warm up we push a button, the 0w10 whooshes into its holding tank and then the 10w30 fills the crankcase. Just before shutting down you push the other button and switch back to the 0w10 for the next cold start. Of course, by 3000 miles you will probably have mixed the residual into each to the point you will be running 5w15 and 5w20 or something like that.

 

[Woody]

quote:

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Originally posted by TallPaul:
I lost oil pump prime once and had to pull the filter and backfill the pump outlet with an oil squirter. There is a FAQ on it in the Filter Council FAQs or the Hastings Filters site, IIRC.

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I lost the oil pump prime on a oil change once too, and the engine was hot. I don't know if the engine being hot had anything to do with loosing the prime, but I've never changed the oil hot since.

 

[davefr]

So if you don't "mix up the oil" where are all these contaminants going to hide?

Last time I looked, my car had only one oil pan for everything. I'll look again today but can't find this mysterious hiding place for contaminants other then the filter.