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My Dads Oil Change Theory

Several months ago, I inherited a 1999 Lexus GS 400 from my Dad. He loved to keep the car in good mechanical condition and that included changing the oil and filter every 5,000 miles. He was a stickler on leaving the oil drain “until there is 20 seconds between drips” from the oil pan to the catch pan. I always thought this would not leave enough residual oil in the engine and lead to a “dry” start, damaging the engine. However, the car runs fine and has 158,000 miles on it. Should I continue with Dads “20 second theory?”

Twenty seconds or one second, it makes no difference,It’s just not important.

You would have to leave the drain plug out for two weeks to get a “dry start”…

There is not really any benefit to this “20 second theory” other than getting as much oil as possible out of the sump before refilling with fresh oil, unless you count that you’re killing more time with the oil change. There will always remain some residual oil in the engine. A much more effective (but with increased risk of burns) method of getting the most old oil out is to change the oil while the engine is warm. There will be a dry start any time the oil and filter are changed. The dry start is caused by the oil pump having to refill the oil filter before any oil is circulated throughout the engine, not by draining the sump. You can minimize the dry start duration by filling the new filter with fresh oil before installing, but this only works well if the filter installs straight up and down, otherwise you end up with a mess of clean oil on the ground and probably up your arm. That was my dad’s oil change theory: always fill the filter before installing. He would do it regardless of how the filter was oriented and would pretty much always make a mess, partially because he insisted on an older car but refused to drive one with a small block Chevy (oil filter threads straight up on those).

Once you’re down to a fraction of a quart left in the pan, the pickup can’t reach the oil anyway. If you want to avoid a ‘dry start’ after oil changes, fill the oil filter if you can before installation. The engine has to wait for oil pressure after an oil change until the filter is filled by the oil pump.

If it has worked since 1999 for the Lexus, I’d stick with your dad’s program. Personally, I don’t think it makes much difference how long you wait. Me, I start the car and run it for 5 minutes to heat up the oil so it drains faster, then I stop the engine, undo the plug, and let it drain for about 5 minutes while I replace the oil filter, at which point I replace the drain plug and refill with fresh oil. I never pay attention to how long between drips. This has worked for me on cars I’ve owned from a 1960’s Ford Galaxy to now. I think the 5000 mile interval is the more important parameter.

My dad, he had a similar concern about the oil should be clean as possible after a change, but what he did was after draining the oil, he’d put the plug back in, and fill it back up again, but not with oil, instead with diesel fuel, run the car a few minutes, and drain it out. Then he’d do the actual oil change. I don’t recommend this by the way. Idling the engine with just diesel fuel instead of engine oil in the crankcase seems like it might lead to some bearing damage. But he thought it cleaned out the inside of the engine better. His cars never needed any major engine repairs. But mine haven’t either.

I think you are missing the big picture. he wanted to drain all oil under the 20 second rule for him, Big difference hard to say but typically one puts new oil and filter in before starting, so explain to me how an extra few ounces of oil drained is a concern.

The only way you could have a dry start would be to disassemble the engine and wash the residual oil from the parts. Some residual oil will cling to the internal engine parts for an indefinite period of time. I have evidence to prove this with some oily things I have in my garage.

When you first start your engine, it is very lightly loaded, loaded only enough to run the engine but is not yet under the heavy loading needed to pull the car so the need for full system oil pressure will be lessened.

There is no “dry start” as long as the engine is started within a reasonable length of time. The critical parts, the bearings and cam lobes are still soaked with oil. And the lack of oil PRESSURE for a few seconds is not going to change the course of history, the engine is still well lubricated…

I think the 20 second theory is a bit of overkill because all of the old oil will not drain out no matter how long it’s left sitting with the drain plug removed. Oil will pool in various places in the engine (in the cylinder heads most noticeably) and will only be displaced by fresh oil once running again.

This was dad’s way of making sure the old oil had time drain out. If you want to improve on it, bounce the car a few times to get out even more oil. Bottom line is all the old oil is drained before you reinstall the plug whatever system works for you.

To avoid a “dry start” you’d have to leave about 1 to 2 quarts in of old oil in the motor - not good. So, just drain it all and refill with fresh oil. There is about 1-3 seconds to get the fresh oil into the oil pump to get oil circulating again from the oil pump. This really isn’t a big deal in a warmed up motor as there is oil coating the moving parts. If there is any wear, it is no more than a typical start of a motor after sitting overnight.

I think we can say that what dad did worked for him and will work for you.  

The important thing is you are getting the oil changed on a regular bases, no less often than directed in the owner's manual using an oil that meets the car manufacturer's recommendations.

Your concern doesn’t make sense at all.

What do you mean by oil residue?? Do you mean the amount of oil left coating the pistons/bearings?? If so then that just doesn’t make sense. When you turn your car off at night and let it sit for 10+ hours that’ll be a lot more oil draining from the pistons and bearings (which is insignificant) then what is draining during an oil change.

If you mean the amount of oil left in the pan…well that doesn’t make sense either since before you start up you’ll be refilling the oil pan with fresh oil won’t you???

I’m at a loss what you’re concerned about.

I just change the oil while it is warm. The front end of the car being raised on ramps or jack stands usually points the drain plug downhill, and it will drain pretty thoroughly while you change the oil filter.

The dry start thing is over hyped. I pointed out recently on another thread that you would have to take an oil-lubricated part out of the engine and scrub it twice with Dawn dish liquid to get the oil off of it. Idling for 2 seconds while the oil pressure comes up won’t hurt anything.

The important thing here is to change the oil. Don’t worry about dry starts just make sure the oil plug is back in tight and you refill the oil.

Ditto to what the others said, especially Joseph’s comment.
Personally, I do things that remind me of my late dad, even though I know they’re unnecessary. For you, perhaps this could be one of those things. It’s meaningless mechanically, but perhaps it’ll remind you of your dad.

As to filling the fiter before installing, I do that. I use a $1 turkey baster to draw some oil from the bottle and fill the new filter. It always surprises me how much oil it takes to do so.

Yeah, kind of anal. Doesn’t really make much difference. Just sequence your work so that it has ample time to drain the oil out. What I do though is fill the oil filter with new oil before installing (depending on location). That way, oil pressure comes up faster on the start up.

Sounds like a mild case of OCD.

I think the 20 second rule is a good excuse to crack a beer.

Important: change oil at recommended interval
Unimportant, but feels good to do, and might help a small amount: pre-fill the filter (assuming outlet installs on top)
Unimportant, but harmless: the 20 second rule

Jtsanders has the MOST likely explination.