flush old oil out with new oil?

[CT8]

Originally Posted by motor_oil_madman
A buddy of mine had me change the oil in his truck a while back cause he couldn't do it. He told me to take half a quart of new oil and pour it in after the oil was drained and the plug was still out. I never thought, but the new oil I just put in came out black like the old oil. I thought that was interesting and wondered how big of a difference that made flushing out more of the old oil doing that.

Opinions?

Because?

 

[FCD]

Seems like a waste.
What i think is a better idea is buying a cheap oil or running leftovers for a short oci instead, which is what i am doing in my Escort right now, used 3 different leftover oils i had, i'll run it and dump it in about 600 miles and then change the oil and filter.

 

[Lubener]

Originally Posted by crainholio
I push a few large syringe fulls of leftover new oil down the dipstick tube after the oil pan has drained. For the 4Runner, I put the vehicle passenger side on ramps front & rear, as the drain plug is on the driver's side. Dipstick is on the passenger (high) side, so oil fed there should flow across the pan floor and maybe help wash any gunk out the drain hole. Or at least push gunk away from the oil pump pickup screen area of the pan.

This is on my project vehicle that was run at 22-25K OCIs by the original owner, and sludge is still being pumped into the filter as shown in the pic below. Here be sludge.

I'm using leftover fractional bottles of whatever 5W-20 or 5w30 are on the shelf. Can't state conclusively that it helps, but it certainly can't hurt and is only wasting ~75mL of oil.

Wow! What a waste of time. The time would be better spent changing the air in the tires.

 

[Hall]

Originally Posted by Lubener
Wow! What a waste of time. The time would be better spent changing the air in the tires.

Remember, there are folks here that let their oil drain for hours or even overnight. I mean, those add'l 5 ounces are critical !

 

[Hall]

All these comments about this being a waste of oil yet how many people still change their oil every 3000 miles ? Or change synthetic oil every 5000 miles ?

Then turn around and get an oil analysis done and the lab suggests "run it longer" but they ignore that.... Typical defense is "$37 is a lot less expensive than a new engine". I guess the thing is, the OP asked for "opinions" and he is getting them.

 

[Patman]

Originally Posted by pitzel
They used to commonly refer to that as the "Patman flush" around here, modelled after the user, Patman, claiming he did that to his Corvette.

Seems very wasteful. Better long-term results probably would arise from simply doing an extra oil change "the normal way" every 4-6 oil changes, if you subscribe to the theory that more oil changes are better.


I had two different ways that I did the Patman flush back in the day. One was the method described here, pouring a half or a full quart into the engine with the drain plug open. I did this when switching over to a different oil, to try and get out more of the old oil so that the first UOA was closer to a 100% concentration of that oil as opposed to 85 or 90%. The updated version of the Patman flush was slightly better though, in that case I'd drain the oil completely, put the drain plug back in and pour about 2 or 3 quarts of fresh oil, of the same brand I was going to be switching to, then idle it for a minute, then drain that oil. Wasteful? Most certainly! And in hindsight, it gave that first UOA with the new oil an unfair advantage since most used oil analysis on here are not 100% pure fresh oil, but there is about 10-15% of the previous oil (with corresponding wear metals) in there too. I haven't done this method in at least 10 years now, maybe more (this was something I did back in the days of switching cars over to GC 0w30)

 

[Lubener]

Originally Posted by hallstevenson
Originally Posted by Lubener
Wow! What a waste of time. The time would be better spent changing the air in the tires.

Remember, there are folks here that let their oil drain for hours or even overnight. I mean, those add'l 5 ounces are critical !

Draining the oil hot will take the dirt with it when its drained and 99.999999% of the oil will be in the drain pan.

 

[Patman]

Originally Posted by Lubener

Draining the oil hot will take the dirt with it when its drained and 99.999999% of the oil will be in the drain pan.


I might be misunderstanding what you mean, but 99.9% of the oil is not going to be in the pan when you drain the oil. No matter how long you let your oil drain, you'll only be able to get about 85-90% of the old oil out. The rest of it will be stuck in oil passages, oil pump and in the valvetrain.

 

[Omahaug]

Ridiculous waste of good oil.

As mentioned, the engine is full of dirty oil all over, in the oil passages, the top end, all of the working surfaces, any attempt at removing more old oil is a losing battle, nobody is ever going to get ahead of it.

Does he run the fuel tank completely dry every single time as well? Siphon the fuel out so that the next tank is completely fresh?

 

[cb450sc]

I used to pour a couple of tablespoons of fresh oil in the engine after the old oil had drained for 30 minutes. Then let it sit another 15 minutes to drain. Now I remember to do it maybe every other oil change. Don't know if it helps but makes me feel better and doesn't waste much oil.

 

[Lubener]

Originally Posted by Patman
Originally Posted by Lubener

Draining the oil hot will take the dirt with it when its drained and 99.999999% of the oil will be in the drain pan.


I might be misunderstanding what you mean, but 99.9% of the oil is not going to be in the pan when you drain the oil. No matter how long you let your oil drain, you'll only be able to get about 85-90% of the old oil out. The rest of it will be stuck in oil passages, oil pump and in the valvetrain.

10-15% left, I doubt it. That could be near 1/3-1/2+ quart, never had that in any car I owned, assuming filter is changed too. If you change oil hot, it will mostly be in the pan at that point.

 

[atikovi]

Originally Posted by JerryBob
Sounds like a complete waste of oil. You're not thinking that the new oil is getting everywhere in the engine, flushing out the old, right? It's going straight down into the oil pan and out.


I would disagree. The route from the filler hole to the oil pan drain hole isn't direct. The oil flows around the head, maybe through the front cover and finally in the pan before finding the drain hole. If more dirty oil gets flushed out, I'd say it's a valid routine. My only comment is if the oil looks that dirty, it should be changed more often, then you wouldn't need to do this. If after an oil change the oil on the dipstick (after letting the engine idle a minute)(diesels excluded) isn't as clean as the oil that comes out of the bottle, the oil was so dirty because you haven't been changing it frequently enough.

200,000 mile Honda after oil change

159,000 mile VW

 

[crainholio]

Originally Posted by Lubener

Wow! What a waste of time. The time would be better spent changing the air in the tires.


Possibly. I was curious, current fill was at ~4600mi and would hit 5K around Christmas when I'd be busy, so I did a change after work today. Same procedure I described earlier in this thread, passenger side on ramps, engine hot after the ~61 mile highway drive home. Let it drain fully while I had supper, then installed a white paper towel over the drain pan as shown in the pics below. I pushed 2 big syringes of RP Racing 21 that's been on the shelf for nearly a decade down the dipstick tube on the high side of the engine and let it drain fully. Impressed with the amount of sludge particles it brought out, I swapped in another paper towel and repeated as shown in the second set of pics. Third time brought out nothing significant, so I reinstalled the drain plug and refilled. Pennzoil Platinum High Mileage 5w30 old fill and new.

Note the brown color of the first paper towel...not Royal Purple purple until paper towel #2. Back to the OP's point, it pushed out quite a bit of old oil in the process that would not otherwise have drained.

You might still believe this is a waste of time, but I'm glad this sludge isn't in my oil pan. The original owner ran up 164K miles at ridiculous 20K+ mile OCIs with Mr. Good Lube oil (yes, that was the name of the place in CarFax records). It's had a tough life.

 

[Patman]

Originally Posted by Lubener

10-15% left, I doubt it. That could be near 1/3-1/2+ quart, never had that in any car I owned, assuming filter is changed too. If you change oil hot, it will mostly be in the pan at that point.


Nope, you're wrong. With any engine, you're not going to get 99% of the oil out at oil change time. It's simply impossible. On my Corvette, it holds 7 quarts but only 6 comes out at oil change time. And just ask owners of the Mazda RX8, they only get about 2/3rds of the oil out, due to the oil cooler and plumbing.

 

[Talent_Keyhole]

Originally Posted by Patman
Originally Posted by Lubener

10-15% left, I doubt it. That could be near 1/3-1/2+ quart, never had that in any car I owned, assuming filter is changed too. If you change oil hot, it will mostly be in the pan at that point.


Nope, you're wrong. With any engine, you're not going to get 99% of the oil out at oil change time. It's simply impossible. On my Corvette, it holds 7 quarts but only 6 comes out at oil change time. And just ask owners of the Mazda RX8, they only get about 2/3rds of the oil out, due to the oil cooler and plumbing.


I agree with Patman, I have re-built multiple engines over the past 30 years. In the old days with a single cams, one main galley feed the cam and crank, flat tappet lifters, most the oil would drain out. These days with engines with 2-4 cams, 16-32 hydraulic lifters, 2 oil galleys and multiple VVT solenoids and actuators per head, use of cartridge oil filters, 10-20% is quite normal for remaining oil.

Machinery Lubrication by Noria has a good article about Short Volume Oil Changes (SVOC). Attached is picture of two oil samples I took this weekend. I am planning to begin long drain OCIs and will be completing a partial fill and drain in between each. The first is a sample that will be tested for a reference fluid, the second sample is the same oil after operating the engine for about 15 minutes. The engine had recently had the pistons/rings/rod bearings replaced, head cleaned and valve job, and oil pan, cam chain, and valve cover cleaned. Although it has 90K, it is close to new engine as you can get. I figured the oil would be a little dark but I could not shine light through it after only short time and mixing with the old oil. It looks clean on the dipstick as expected.

https://www.machinerylubrication.com/Read/31012/short-volume-oil-changes