A thought on changing oil when hot or cold.

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3,542
Location
Colorado
I always change my oil when it is hot. It folws better and that should cause it to get more oil out then when it is cold. A friend of mine changes his when it is cold because he says after it the car has been sitting for awhile all the "grit" in the oil is at the bottom of the pan. He says when you change it when it is hot after just running it all the "grit" is now all over the engine and not in the pan so it stays in the engine. Does he have a point? I know when you take a sample for UOA it says to take when the oil is hot.
 
Messages
714
Location
Pennsylvania
quote:
Originally posted by Chris B.: I always change my oil when it is hot. It folws better and that should cause it to get more oil out then when it is cold. A friend of mine changes his when it is cold because he says after it the car has been sitting for awhile all the "grit" in the oil is at the bottom of the pan. He says when you change it when it is hot after just running it all the "grit" is now all over the engine and not in the pan so it stays in the engine. Does he have a point? I know when you take a sample for UOA it says to take when the oil is hot.
I change it a 'little' after hot...to a) let whats in the heads and is gonna drip off stuff - drip and b) not give me that severe of burns (look at the bright side - gm abandoned that gosh darn PJ1072 'filter in the pan' setup on the iron duck) I HATE the smell and feel of used oil on my skin (only brake fluid is worse in my book)
 
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3,202
Location
Far North East Texas
Hot oil holds more cooties in suspension, so draining oil hot gets more cooties out of your engine. Draining cold is much better than no oil change at all, but not as good as draining hot. At least that's what the big boys say. I've always drained hot.
 

Patman

Staff member
Messages
22,011
Location
Guelph, Ontario
I guess mine is a combination of the two, as I like to start it draining right away when it's hot, but then I like to leave it to drain for an hour or two. This should get rid of most of the old oil in the engine (other than what is stuck in the oil pump or trapped in any other "pockets" in the engine)
 
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23,591
quote:
He says when you change it when it is hot after just running it all the "grit" is now all over the engine and not in the pan so it stays in the engine.
Well, if the grit (if there's any) collects in the pan, then it probably won't really drain out of the pan after settling there. Instead that sludge will mix with fresh oil and start to circulate once again in the engine. I drain the pretty hot oil, making sure I see the last drop (as if there were!) fall. That means I let it usually drain for at least 45 minutes, with the car slightly tilted towards the drain opening (driver's side). [ July 14, 2003, 02:28 PM: Message edited by: moribundman ]
 
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4,844
Location
Saskatchewan
[/QUOTE] I HATE the smell and feel of used oil on my skin (only brake fluid is worse in my book) [/QUOTE] Used oil feels and smells great. Well, maybe only compared to gasoline (**** under-the-car fuel filters)! I've only tried a cold oil change once. I don't know if it was because the oil that came out was fairly dirty, but the new stuff looked pretty brown right away after startup. I'll stick to the hot oil changes. [ July 14, 2003, 02:30 PM: Message edited by: rpn453 ]
 
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211
Location
CMH
the real reason for changing when hot is to be able to refill the system while there is still a layer of oil all over the engine. ie after say 4 hours, the cylinders are not coated with much oil, so starting tyhe engine and running it for the few extra seconds it takes the ump to pressurize the drained system can theoretically do more damage. I like to drain while hot and let it drip while I install the filter.
 
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47,817
Location
Everson WA - Pacific NW USA
I'm not biting on this "grit" thing. How much grit is your oil??? So much that it won't come out when you drain it hot??? a) if the true "grit" is big enough, that's kinda why you have an oil filter and should change it wid da oil b) iffen you have this "grit"s in your oil - where the heeck is it comin' from? Find it and fix it. Now I do believe in allowing a 3 beer (or 1 long diversion, if you know what I mean) for the oil to drain, to allow all this "grit" to come out wid da earl....so by the time you are feeling all better (and you KNOW what I mean) - the grit gone gone all da betta.
 
Messages
23,591
quote:
ie after say 4 hours, the cylinders are not coated with much oil, so starting tyhe engine and running it for the few extra seconds it takes the ump to pressurize the drained system can theoretically do more damage
I don't know about your engine, but mine has oil retention valves that prevent all oil from drainig back into the sump when turning the motor off. A fair amount of oil is kept close to the cams at all times. I'm also a believer in prefilling the new oil filter. And yet, I'm still staring at the oil light when starting up the engine after an oil change. [Wink]
 
Messages
824
Location
San Jose area, CA
I am not sure about the "grit or cooties" that is spoken of, unless someone has had oil filter clogging and for whatever reason the oil filter has ceased to filter. As is well known or advertized, quality oil filters filter to 25-40 microns!!?? [Confused] The other thing that is apparent is that two of my 4 vehicles, VW Jetta TDI and Z06 have a complicated oil dipstick measuring procedure. What happen to the days of: wipe the dip stick, put it back in and pull it out for a accurate reading, while the engine is "not running"?????? The VW Jetta TDI specifies a lag period, after shut down, but stops short of giving a specified number of minutes. [I dont know] The upshot is that if you take a dipstick reading after it has been sitting all night(for example) the measurement is inaccurate (usually overfilled)!!!! Now normally this is no big deal, but the VW OEM is ADAMANT that if you experience engine failure due to filling past the "full" hash mark during the 50,000 warranty period they WILL DENY WARRANTY service. The Z06 Corvette is even more "loosy goosy" but does not have the warranty gun to the head!!! Again, the bottom line is: an over night reading is inaccurate and in fact the full line does not really mean full and the add line does not really mean add [LOL!] To add to the mixture it says that if you track the vehicle or corner exuberantly you should add in a full quart EXTRA. So by process of elimination it seems that sitting overnight, which probably means it is "cold" when you do an oil drain, you will drain from a greater pool of pooled oil !!! [Duh!] And to add, again if the oil holds the grit or cooties in suspension and if over time the grit or cooties sink to the bottom of the oil pan/sump, doesn't that by process of elimination make sure the grit or cooties go to the bottom of the pan instead of being suspended somewhere other than the bottom of the oil pan? Which is what you want anyway? [ July 14, 2003, 03:31 PM: Message edited by: ruking77 ]
 
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5,358
Location
Gone
I change the oil when hot...this is a case of "everything I've heard and read says do it that way to get the...ahem...'cooties'out"...I do have an exception: my son's 94 Nissan Hardbody Truck..the filter is RIGHT UNDER the exhaust manifold...yes I have burned myself.
 

Patman

Staff member
Messages
22,011
Location
Guelph, Ontario
quote:
Originally posted by pscholte: I change the oil when hot...this is a case of "everything I've heard and read says do it that way to get the...ahem...'cooties'out"...I do have an exception: my son's 94 Nissan Hardbody Truck..the filter is RIGHT UNDER the exhaust manifold...yes I have burned myself.
That's why my method works in a case like that, because if you've let the oil drain for one or two hours, by the time you do change that oil filter it will have cooled off.
 
Messages
211
Location
CMH
[/QUOTE]I don't know about your engine, but mine has oil retention valves that prevent all oil from drainig back into the sump when turning the motor off. A fair amount of oil is kept close to the cams at all times. I'm also a believer in prefilling the new oil filter. And yet, I'm still staring at the oil light when starting up the engine after an oil change. [/QB][/QUOTE] okay I was unclear then, the oil system is drained when you remove the filter, prefilling the filter is good and I do it as well, but starting the engine after the change still requires more time to fill the system. [ July 14, 2003, 04:44 PM: Message edited by: got boost? ]
 
Messages
56
Location
Los angeles, CA
You raised an interesting question. I have always drained while semi-hot thinking it flows better out the plug. But your saying when I drive around a few blocks before changing it is letting all the grit or cooties swish around and being left behind makes sense too. Because theoretically when I parked the car the night before the engine and oil was hot, so theoretically all that grit and cooties should have dripped into the pan when its hot and had all night to drip. Although I always thought if I didnt drive around a few blocks the following morning to heat the oil up, that cold oil would not completely drain and stay in the pan, causing the same grit and cooties to be left behind with the new oil to swish around. Wow now I am confused. [I dont know]
 

Patman

Staff member
Messages
22,011
Location
Guelph, Ontario
If you guys are really worried, do it this way: 1.drain it hot 2.fill with fresh oil 3.drive it 10 miles 4.let car cool down overnight 5.drain oil cold 6.fill with fresh oil again [Smile]
 
Messages
714
Location
Pennsylvania
quote:
Originally posted by Patman: If you guys are really worried, do it this way: 1.drain it hot 2.fill with fresh oil 3.drive it 10 miles 4.let car cool down overnight 5.drain oil cold 6.fill with fresh oil again [Smile]
or...take out motor, take off pan, take off intake, use high pressure kerosine wash, install new pan, install motor, install oil repeat every 3000 miles
 
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2,480
Draining should be done when warm not hot (although not always possible) because cold oil will take forever to drain out (more viscous) and will hold less contaminants as they have been give too much opportunity to settle in the bottom of the pan or elsewhere....
 
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5,358
Location
Gone
Well, I like QD's suggestion, but I think I would have to allow more than 30 minutes to do it...I hurt my back once trying to lift the engine too quickly out of the engine bay (did I hear someone say "hoist"; what's a "hoist"). I REALLY like Patman's idea because then I could say to my wife, "Honey I really do need all that oil down there in the basement; by the time I use the "flushing oil" and the oil for the change..."
 
Messages
34,375
Location
NJ
quote:
or...take out motor, take off pan, take off intake, use high pressure kerosine wash, install new pan, install motor, install oil repeat every 3000 miles
[LOL!]
 
Messages
246
Location
Atlanta, GA
I'm not saying to change it cold, but the hotter it is , the more likely I am to drop the oil plug into the drain pan, and with the closed top type, if it makes it down that hole it's a real real pain. [Bang Head]
 
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