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10/20/2017 1:01:18 AM
9/22/2017 12:11:25 AM
Posted: 9/12/2005 5:17:47 AM EDT
Let me preface this with the following:

I know conventional wisdom says to change the oil hot, since it's been recirculating around the enging and all and has more dirt picked up. Now follow me on this line of reasoning:

1) Let's assume a real stupid contamination, like 1oz contaminants per 1qt, just to keep it simple.
2) Oil is settled in certain spots where it won't drain out of the engine - let's say that amounts to about 1qt as well.
3) Whether the oil is hot or cold, you'll never get that 1qt out - agreed?
4) You have 1oz contaminant stuck in that 1qt as mentioned earlier - since you can't get that 1qt out, does it make a difference if I change the oil on a hot or cold engine?

So what makes changing the oil on a hot engine better? Let's hear some scientific explanation, not hearsay...
Link Posted: 9/12/2005 5:24:24 AM EDT
because it drains out quicker. that's why i do it, i have one of the sure drain deals and never have to touch it while hot. other than that, i say it's up to you.

oldsaltydog
Link Posted: 9/12/2005 5:24:49 AM EDT
I will continue to change hot until further evidence is produced
Link Posted: 9/12/2005 5:25:13 AM EDT
Drains quicker and more effectively.
Link Posted: 9/12/2005 5:28:33 AM EDT
warm engine.
MB dealerships use a vacuum pump and suck it right out of the dipstick tube. From what I hear it's very effective
Link Posted: 9/12/2005 5:29:14 AM EDT

Originally Posted By oldsaltydog:
because it drains out quicker.

Exactly!
Link Posted: 9/12/2005 5:30:00 AM EDT

Originally Posted By captainpooby:
Drains quicker and more effectively.



Doesn't get any simpler than that. Of course I wait about 20 minutes or so to let as much oil as possible get back into the pan and to cool down some so as not to burn myself.
Link Posted: 9/12/2005 5:32:15 AM EDT
Start your vehicle up. Drive it around the block, let it it cool for a few minuntes. Drain oil.
Link Posted: 9/12/2005 5:32:44 AM EDT
I'll open the pan hot and let it drain for a couple hours on a Sunday afternoon.
Link Posted: 9/12/2005 5:33:47 AM EDT
I always change the oil cold.

I leave my car on a lift in the shop(grounded not raised) or in the driveway at home and let the vehicle sit over night so as much oil as possible goes to the pan. Then I drain it the following morning .

But on the rare occasion I'll let a mechanic change the oil while the vehicle is hot but thats rare indeed.

But Ive never seen a technician change the oil cold they always bring them in and change the oil quickly then repeat.

You'll never get all the oil out of the motor though.
Link Posted: 9/12/2005 5:41:39 AM EDT
If you really want to clean it all out change it with the cheapest oil you can find then warm it up and change it again with the good stuff.
If I was going to sell a car, this is what I would do,
Link Posted: 9/12/2005 5:41:47 AM EDT
If it was just a matter of changing the oil, I'd change it very warm or hot. However, there's usually a filter involved (almost always located in an inconvenient spot), so I wait until the engine cools to a manageable (not painful) level. Then I dump the oil and remove/replace the filter.
Link Posted: 9/12/2005 5:43:10 AM EDT
It's usually only as warm as it can get from pulling it from the driveway into the garage. I change the oil often enough that it doesn't make a difference in the grand scheme of things.
Link Posted: 9/12/2005 5:43:31 AM EDT
Warm engine
Link Posted: 9/12/2005 5:51:00 AM EDT
Hot engine.

Now, if you're worried about residual contamination, do what I do every now and then:

1) Hot drain.

2) Refill with cheap oil. Run 5 minutes. Drain.

3) Repeat step 2) once more if desired.

4) Replace oil filter and fill up with good oil.


For REAL cleaning, add a can of SeaFoam and run the engine for 20 minutes before Step 1.
Link Posted: 9/12/2005 6:04:01 AM EDT

Originally Posted By CWO:
Warm engine




+1.

No use in burning yourself, both on the car or with the oil.
Link Posted: 9/12/2005 6:12:54 AM EDT

Originally Posted By captainpooby:
If you really want to clean it all out change it with the cheapest oil you can find then warm it up and change it again with the good stuff.
If I was going to sell a car, this is what I would do,



I did that with my motorcycle (accidentally put in the wrong type of oil) and my oil looks nice and clean. Not sure if it's worth the hassle, though.
Link Posted: 9/12/2005 6:27:16 AM EDT
I do the dual change about every 25 thousand miles. I go the whole way and change both the oil and filter twice. On the first of the two I used a thinner oil and I run the vehicle for a day or so and then do another change back to my regular oil. Really seems to clean out the block nicely.
Link Posted: 9/12/2005 6:34:19 AM EDT
When i worked at a ford dealership, if there was a worry of contaminents in the oil, remove the drain plug when the engine is warm, start the car, and pour oil into the engine with the drain plug removed. It'll cirulate and pump the system clean. Unless you sit there and rev the engine it wont do any damage. You are right though, there is a small amount that doesnt drain out.
Link Posted: 9/12/2005 6:39:08 AM EDT
OK - a lot of you have mentioned that you change your oil hot. That's fine, and I do agree that the viscocity is lower and you'll get *slightly* more oil out. On the other hand, very few of you which replied "hot" mentioned WHY, which is really what I'm looking for.
Link Posted: 9/12/2005 6:42:42 AM EDT
I drain mine warm but not hot. My oil filter is hard to reach, and I don't want to burn myself. Cold doesn't seem to drain quite as well.
Link Posted: 9/12/2005 6:55:11 AM EDT
Warm enough that the oil still flows really well, cool enough that a good percentage of it and contaminants have drained into the pan.....
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