Hot or Cold oil change?

SR5

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5,433
I was always told to do an oil change when the oil was hot or warm, I think the logic was that more contaminants were in solution and the oil drained out faster. But now I think on that logic, if the oil needs heat to keep contaminants in solution then I should have changed the oil long ago and I already have an engine full of sludge and varnish. With modern thin synthetic oils used over reasonable intervals, does it make any difference if you change the oil hot or cold ?
 
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I've always done it hot but you add a interesting point. I started back in the days of SAE30 grade. The oil drained easier and better when hot. Now with 0w20, maybe it doesn't matter that much? On the other hand, draining it hot also means stuff is suspended better so you might be getting more stuff out that would otherwise build up inside. I'm still on my first cup of coffee here at 0230 so my brain is not yet activated.
 
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Warm or hot oil indicates to me the contaminants are in suspension, and warm oil drains quicker and easier in cold weather. That's how I was taught well over 40 years ago and I stayed with it.
 
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I've always done them cold because i don't fancy getting my arm or hand burnt touching a hot exhaust or oil. And as we know, on BITOG the ultimate performance spec is : "It hasn't blown up yet" And certainly i have never had an engine blow up yet from doing oil changes cold lol
 
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Originally Posted by PimTac
On the other hand, draining it hot also means stuff is suspended better so you might be getting more stuff out that would otherwise build up inside.
I have to ask where do the contaminants go when the oil is cold? As the engine cools and the oil drains back to the pan do the contaminants get left behind. Just trying to wrap my head around this because I don't change my oil any longer so when I take it to the quick lube the oil is warm but when I leave it with my mech it's usually the night before so I know he's not letting it warm up so if this is an issue I might consider going back to the quick lube.
 
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Originally Posted by Duffyjr
Originally Posted by PimTac
On the other hand, draining it hot also means stuff is suspended better so you might be getting more stuff out that would otherwise build up inside.
I have to ask where do the contaminants go when the oil is cold? As the engine cools and the oil drains back to the pan do the contaminants get left behind. Just trying to wrap my head around this because I don't change my oil any longer so when I take it to the quick lube the oil is warm but when I leave it with my mech it's usually the night before so I know he's not letting it warm up so if this is an issue I might consider going back to the quick lube.
Mind you, I'm a bit old school so this might not apply as much as it did 45 years ago with thicker oil. It was the thinking then that stuff settled in the pan. In that era engines ran dirty and sludge was a battle. This is a interesting point that SR5 is trying to bring up. I do the change hot because of beliefs that are decades old. Maybe they don't apply anymore? In either case I still drain the oil hot as I've done for decades. Old habit I guess.
 
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Modern synthetics still drain a lot slower from a stone cold engine, especially during the winter. I would imagine there is also some slight condensation in a cold engine, that would otherwise be burnt off had the engine been driven long enough prior to changing the oil. Which brings up more questions. If you're going to run the engine prior to changing the oil should it be run long enough to burn off excess fuel and moisture? Or change it cold? Truth be told I'm sure there are millions of DIY'ers who change their oil cold and drive 100's of thousands of miles doing so.
 
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I do whatever is convenient. Also, if the filter gets unreasonably hot due to its location from say the exhaust, I'd just dump everything cold. Contaminants should be kept in suspension even on a cold engine (assuming its DD'd and hasn't been sitting), but getting everything stirred up certainly won't hurt and it'll make everything flow out faster since it'll be hot. On a side note, various manuals for all sorts of auto fluids say to run before dumping, which IMO is important on stuff without filters like diffs and PS systems and arguably less on engines with filters.
 
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I have done it both ways... Scalding hot and stone cold... Like demarpaint said in the winter a bit of heat is very very helpful... When I changed the oil in my Altima several years ago it was like 14°F or -10°C with a wind chill below 0°F... I am glad I warmed the car up for several minutes prior to starting that fun experience.
 
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Ohh and by the way... Very good to see you on here. I hope that you and your family have been doing good.
 
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Originally Posted by SR5
I was always told to do an oil change when the oil was hot or warm, I think the logic was that more contaminants were in solution and the oil drained out faster. But now I think on that logic, if the oil needs heat to keep contaminants in solution then I should have changed the oil long ago and I already have an engine full of sludge and varnish. With modern thin synthetic oils used over reasonable intervals, does it make any difference if you change the oil hot or cold ?
You could argue it shouldn't.... But why? If you have particulate matter in a liquid, mixing that liquid right before you drain it from whatever container is going to leave less of it at the bottom. Add to that being hot makes ANY motor oil, regardless of it's viscosity, drain faster and more completely. Especially off of hot engine parts, of which there are many. Which helps contribute to all of this in a positive manner. You have 2 choices when changing oil. Do it hot or cold. I can't see any possible advantage to doing it cold, other than you won't possibly burn your hands. And most everyone who takes their vehicle in for an oil change, has it done hot. As do most people who do their own. So what percentage does that leave of cars that have cold oil changes performed? It has to be an all but insignificant number. You might say this is one case where, "running with the sheep" won't get you slaughtered.
 
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Originally Posted by PimTac
Originally Posted by Duffyjr
Originally Posted by PimTac
On the other hand, draining it hot also means stuff is suspended better so you might be getting more stuff out that would otherwise build up inside.
I have to ask where do the contaminants go when the oil is cold? As the engine cools and the oil drains back to the pan do the contaminants get left behind. Just trying to wrap my head around this because I don't change my oil any longer so when I take it to the quick lube the oil is warm but when I leave it with my mech it's usually the night before so I know he's not letting it warm up so if this is an issue I might consider going back to the quick lube.
Mind you, I'm a bit old school so this might not apply as much as it did 45 years ago with thicker oil. It was the thinking then that stuff settled in the pan. In that era engines ran dirty and sludge was a battle. This is a interesting point that SR5 is trying to bring up. I do the change hot because of beliefs that are decades old. Maybe they don't apply anymore? In either case I still drain the oil hot as I've done for decades. Old habit I guess.
Thanks and nothing wrong with old school if it works. So the contaminants settle to the bottom of the pan and don't drain out when cold so it can build up and then mix back in the fresh oil, I can see this being an issue down the road.
 
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I've always been told to do it when hot because the contaminants are held in suspension when the oil is hot, otherwise they settle on the bottom of the pan and the oil will flow right over it as it drains...leaving them in there. Don't know how much I agree with that, so I usually just do it when it's warm...I'm not into burning myself and having hot oil splash all over me.
 
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Originally Posted by billt460
Originally Posted by SR5
I was always told to do an oil change when the oil was hot or warm, I think the logic was that more contaminants were in solution and the oil drained out faster. But now I think on that logic, if the oil needs heat to keep contaminants in solution then I should have changed the oil long ago and I already have an engine full of sludge and varnish. With modern thin synthetic oils used over reasonable intervals, does it make any difference if you change the oil hot or cold ?
You could argue it shouldn't.... But why? If you have particulate matter in a liquid, mixing that liquid right before you drain it from whatever container is going to leave less of it at the bottom. Add to that being hot makes ANY motor oil, regardless of it's viscosity, drain faster and more completely. Especially off of hot engine parts, of which there are many. Which helps contribute to all of this in a positive manner. You have 2 choices when changing oil. Do it hot or cold. I can't see any possible advantage to doing it cold, other than you won't possibly burn your hands. And most everyone who takes their vehicle in for an oil change, has it done hot. As do most people who do their own. So what percentage does that leave of cars that have cold oil changes performed? It has to be an all but insignificant number. You might say this is one case where, "running with the sheep" won't get you slaughtered.
I agree. I'm going to stick with the way I was taught. Drive the vehicle, let it cool while I gather my tools and change the oil warm to hot. I have a nice pair of oil proof rubber gloves that protect me against burns if needed.
 
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I don't think being hot makes any difference since the oil does not freeze when cold. Or is there something am missing?
 

SR5

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5,433
Originally Posted by KingShalamar
I don't think being hot makes any difference since the oil does not freeze when cold. Or is there something am missing?
Your first post, Welcome!!! Thanks for joining in.
 

SR5

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5,433
Originally Posted by bbhero
Ohh and by the way... Very good to see you on here. I hope that you and your family have been doing good.
Hi BBhero, always good talking with you.
 
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4,215
The job of the lubes dispersants is to hold particles (like soot) in a solution. If I'm not mistaken, dispersant chemistry envelopes the particulates and does not permit it to settle out or accumulate (form larger particles), holding it in suspension so it can be filtered or drained out. Will you get some at the bottom of the pan, maybe I suppose in the form of sludge but if the lube is doing it's job and the additives (like detergents) are not being depleted during an extended drain interval..it should be minimal, right? Then why would the lubes dispersant chemistry not work or be less effective when cold?
 
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Collecting the sample after a short engine run will likely show higher fuel dilution if you're doing an oil analysis. Of course, after a long run, the engine could be allowed to cool before collecting the sample. I've changed oil on fairly large engines (V12 Twin Turbo, 1200 HP, MANN Diesel). If you don't warm-up the engine first, you'll be there all day waiting for it to drain. A significant amount will never drain out. If it's a pump-drain engine with inaccessible drain plugs, on a cold day, the pump circuit breakers will trip before any oil ever comes out.
 
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Draining the oil hot means (and should mean) the engine was recently running churning up ALL contaminants (those suspended by the oil and those that are not). Back in the day I always changed my oil cold. I think differently now and enjoy watching the oil race to the drain pan instead of watching it gurgle down.
 
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