Changing oil when engine is cold.

Messages
226
Location
Virginia
I'm looking for some informed opinion about the necessity of warming the engine before changing the oil, which I've been doing for the past 30 yrs. I have 3 low mileage vehicles to change every 4 mos. with dino since they are used 90% of the time for short trips. I could probably save about 25% of the time involved if I didn't drive each one first to bring it up to operating temp which I doubt the dealer shops bother to do. I will probably not reach 100K miles on any of them but would like to be able to sell them or pass them along to relatives knowing that the engines don't have excessive wear. Thanks.
 
Messages
903
Location
CA
I don't see there being much of a difference. It's not like you need to stir up the rocks and metal shavings sitting in the oil pan to get them out.
 
Messages
3,683
Location
Chattanooga, TN
I think that part of the argument for hot is that when the contaminants settle to the bottom over time as the engine cools the opening of the plug is not sufficient force to carryout the contaminants and they settle on the bottom and stay there. In hot oil there are still suspended in the oil and will flow out. Whether true or not???
 

CJH

Messages
489
Location
Pennsylvania
Even if you don't let the engine come fully up to operating temperature, I think you should run it a little to circulate the oil and get all the contaminants in suspension prior to draining. [ May 11, 2003, 10:28 AM: Message edited by: CJH ]
 

Jay

Messages
1,607
Location
Idaho Falls, ID
How much of the old oil do you wish to drain? If you want to drain most of it out then warming it up speeds the process considerably.
 
Messages
9,448
Location
USA
In my opion I do not see any staticly significant reason for bringing the oil up to temp. While the additives do function best at operateing temp the natural hydralic forces of runing the engine to move the vechile into place and then draining the fluid should be enough to make sure that all of the contaminets are in susepension. The practice of warming the oil is often not practiced by anyone in the industry. Like wise another practise that I was taught as a young aprentice of pulling the coil wire and dry cranking the engine to remove all possable used oil is also not in favor these days. If the oil is doing it's job and the owner is doing his the oil should be changed before the additives lose their ability to keep the byproducts in susepension(sp).
 
Messages
3,320
Location
Bolivia
I'm a firm believer in HOT. Also I would never leave the drain plug or filler cap off overnight since dirt will get in (unless you have a dust-free garage).
 
Messages
6,789
Location
Huntington Beach, CA
The oil is warm/hot when the engine us turned off, therefore any contaminants are held in suspension AS the oil is draining to the pan. Assuming the oil pan allows for as complete drain as possible, COLD is the way to go IMO. More oil drained. Also ambient temperature in most cases allows for "cold" oil to drain/flow quickly enough to carry contaminents out of the pan, at least in Southern California.
 
Messages
3,203
Location
Southeastern, PA
I'd recommend changing the oil hot. If the car is not driven frequently / driven on short trips, water condensation in the crankcase could be an issue. Draining the oil cold could leave condensation in the crankcase.
 

Al

Messages
19,163
Location
Elizabethtown, Pa
I'd be willing to bet you get more contaminents by draining hot. The pan will stay hot as the last amount of oil is running out and more oil will run out because it stays hot. I usually allow about an hour drain.
 
Messages
211
Location
CMH
one of the most important reasons for chsnging warm is that the engine has a coating of oil, and less damage occurs when first priming the system after the change.
 

Patman

Staff member
Messages
21,989
Location
Oakville, Ontario
quote:
Originally posted by got boost?: one of the most important reasons for chsnging warm is that the engine has a coating of oil, and less damage occurs when first priming the system after the change.
An excellent point!
 
Messages
4,478
Location
Southern California
quote:
Originally posted by widman: I'm a firm believer in HOT. Also I would never leave the drain plug or filler cap off overnight since dirt will get in (unless you have a dust-free garage).
I agree with the advice but not the reason you give. With a closed garage, I doubt that any significant dust will be stirred up and magically jump through the drain hole. However, by leaving the oil sump unfilled and the engine restarted for any significant length of time, one of the oil filter companies (can't remember whether it was Fram or Champion Labs) suggested on their website that the oil pump might lose its prime. I don't think that water will be much of an issue, either. Since water's specific gravity is greater than that of oil, any in the sump will be the first to drain in a cold engine if the drain hole is at the lowest point and will be carried out as a suspension in a hot engine. Since every owner's manual I've ever had directs to change the oil hot, that's the advice I've always followed. Since I've always followed the advice to change oil and filter every 3,000 miles, too, I doubt I'll change either practice now that I'm fat, bald, old, and crotchety. (Besides, burned fingers give me a good excuse to cut forth with a litany of stirring epithets to entertain the canvassing holy rollers on an otherwise quiet Sunday morning... Their tracts are wonderfully absorbant, but too small. They always wonder why I want a dozen of 'em.)
 
Messages
7
Location
CA
I will run the veh all day, do what ever you need to do for the day, untill I get home, park in my garage, drain the oil, untill next morning, replace the washer, and then replace the oil filter. you want to run the veh hot up so the oil will come out faster, that is the only reason .
 

CJH

Messages
489
Location
Pennsylvania
Another point is that, depending on the ambient temperature and your choice of oils, you may be waiting a long time for cold oil to completely drain from the engine. I think the better practice is to circulate and warm the engine, even if not to full operating temperature.
 
Messages
137
Location
Massachusetts
quote:
Originally posted by CJH: Another point is that, depending on the ambient temperature and your choice of oils, you may be waiting a long time for cold oil to completely drain from the engine. I think the better practice is to circulate and warm the engine, even if not to full operating temperature.
this is the reason I warm up the engine, just so that it drains out quicker. when you get to that last little trickle, if the oil is cold, that trickle tends to last forever!
 
Messages
922
Location
Ontario , Canada
I've done it both ways many times, I've felt that you drain more oil out of the engine when it is cold and the vehicle has sat overnight. More time for the upper engine areas to drain into the pan. just my observation. Joey
 
Messages
277
Location
Greencastle Pa.
Here's clip from a recent Lube Tip's,It's referring to sampling but I can see how a warm well agitated oil will hold the most contaminants when draining,I also remember reading recently but I'm not sure where,on how detergent/dispersant add's can physicly hold more in suspension when hot. Here is an example of how quickly some particles can settle four inches (assuming spherical-shaped particles): 50-micron silica particle: 12 minutes 50-micron steel particle: 2.1 minutes 50-micron copper particle: 0.8 minutes 50-micron chromium particle: 2.5 minutes
 

Patman

Staff member
Messages
21,989
Location
Oakville, Ontario
Since a lot of us on here also take an oil sample when we drain our oil, it's mandatory to drain it when it's hot, otherwise the UOA results won't be as accurate.
 
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