Drain Oil When Oil Is Hot.

[George7941]

Here is what Shell has to say on the subject

http://www.shellusserver.com/qa/answerresult.php?rowid=13


I always do engine oil (and transmission, diff) drains when the oil is hot so that the oil drains out quickly and carries with it as much of the deposits on the bottom of the oil pan as it can. I will not even use a Fumoto or a Sure Drain because I do not want it to impede the flow of the oil.

The 60 to 70% figure Shell uses applies if you start up a cold engine just before you change the oil. Of course it does not apply to a cold engine if you do not start it up before you drain. In this case there will be just a small amount of extra oil clinging to the sides of the oil pan.

 

[Pop_Rivit]

Quote:
Thicker, room-temperature oil clings more to vertical surfaces. It also gets held up in the flat, horizontal spaces inside the engine--in the valve train area, for example


Can I ask how hot oil gets drained from the horizontal valve train surfaces and room temperature oil does not? Wouldn't the horizontal surfaces in the valve train hold more oil right after being shut down as opposed to draining for a few hours? Unless the assumption is that somehow the oil migrates back up into the valve train from the pan as the oil cools.

Maybe it's just luck, but I usually change the oil at room temperature, and if the article were correct I'm only removing 60-70% of the oil when changing both the oil and the filter. Why is it that, when after draining, I refill my oil with the amount specified in the owners manual my dipstick does not show overfilled?

My car doesn't use any oil, so by now I should be at least a gallon or so over full, but it's not.

 

[George7941]

The 60-70% figure is definitely an exaggeration and perhaps the true figure is closer to 95%.

My last paragraph in my original post was an explanation of the thrust of the article. If you run a cold engine for a short while (say a minute) and then drain the oil, more of the cool oil will be hung up in parts other than the oil pan and will not be drained out. It does not apply if the engine was up to operating temperature, shut down and the oil then drained after a few hours. In this case the hot oil would have drained down and accumulated in the pan and then cooled down.

 

[dwendt44]

part of the idea behind draining oil hot or warm is that the oil galleries and the bearings have oil in them. When starting after an oil change, it's there to do its job while pressure builds andthe filter fills.
Another reason the 'pre-fill' a filter. I do so even when they are horizontal.

 

[Cutehumor]

I disagree with the the 60-70% figure. I just changed oil in a 96 Ford Explorer V-8 cold. the engine wasn't started in 4-5 days. the oil flowed out slow of course. But when I filled the engine with my 5 qt havoline bottle, the dipstick read full. if there was 60-70% drained out, I would have been over the max line at least a quart of oil.

 

[mechtech2]

The 60-70 % is nonsense.
We would have to try to get such horrible draining. Only if done intentionally.
What about the advantage of a cold engine having sat for so long, much oil is in the pan that would not be there with a quick hot change? [20-50 in 0 deg F temps would of course be slow.]

And depending on your oil OCIs, letting a filter stay for a repeat performance is perfectly OK. How could a filter be good for 12 -15,000 miles , yet be no good for two 4,000 mile changes?