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Engine Oil Rinse?

One of my co-workers was telling me that he “rinses” his engine by running 1.5 quarts (left from the previous oil change’s 5-qt jug) for about 5 minutes to clean out additional sludge.

This strikes me as being a horribly terrible thing to do to your engine… or is it something that is outdated but won’t really hurt his car?

?? JUST the 1.5 quarts? I don’t understand, but it sounds like a BAD idea…

I’m with texases on this one.

Why does he feel that running the engine for 5 minutes with 1-1/2 quarts of last month’s oil will wash it out any better than 4 quarts of this month’s oil did?

Anyway, it’s a bad idea. If he were using the full 4 quarts of last months oil I’d say it’s useless but harmless. Running it with 1-1.2 quarts is dumb. A tablespoon of contaminants in 1-1/2 quarts of fluid is a much poorer lubricant that a tablespoon of contaminants in 4 quarts of fluid. And if he should estimate a bit off and the oil level drops below the pump’s pickup tube, he’ll demolish teh engine. He’s essentially making sure he does a bad thing before he proceeds with doing a good thing.

Humans. We certainly are a strange species.

I really hope for his sake that we’re misunderstanding this. Could he be draining 1.5 quarts, adding the leftover fresh 1.5 quarts, running the engine for a bit, and then doing a full oil change from there? I doubt that’ll do anything of measurable value, but at least it won’t hurt anything.

If we’re not misunderstanding this, then he’s terribly misinformed. I’d hate to be the next owner of any of his cars!

I think your friend is confusing his car with his washing machine. In the washing machine, you add the detergent to the water and after the wash water has done its job, the washing machine goes into the rinse cycle. While he is, no doubt, using detergent oil in his car, he should not do his rinse cycle. Maybe he needs to get a real old car of the 1940s that didn’t use detergent oil.

Triedaq, allow me the liberty of abusing your analogy.
If my washing machine used 1/3 of a tub of last week’s used washwater to rinse my cloths in, THAN it would be analogous to what the OP is describing.

And lordy, would people avoid me!

Your co worker is pulling your leg. If not, you need to talk to someone else during breaks. Just kidding.

@same "Humans. We certainly are a strange species."
Well said,even understated in this case.

Unfortunately, he’s doing exactly what I described … draining the 3.5-ish quarts in the engine, replacing it with a total 1.5 quarts fresh oil, running it for 5 minutes, then draining that out and putting in a fresh 3.5 quarts + new oil filter.

I’m not an automotive engineer (I’m a backyard mechanic by necessity and a code monkey by day), but I’ve never heard of anything like this and it sounded like a really bad thing to do, so I thought I’d ask.

Agree; a very bad and very stoooooopid idea!!!

These ideas normally originate with persons who could not pass highschool physics and chemistry.

You may not be an eng’neer, but you gots a good head on your shoulders.

In these cases it can be best to just say “oh, that’s interesting…and change the subject.”

Sincere best

In the end, it’s another thing with plenty of talk time in it but not worth the effort to argue about. It’s nice to have the time to try things. I would try things like that if I still had the ability to get off the floor without difficulty. One oil change project a day is enough for me.

For a younger, more enthusiastic person, I would recommend nothing but playing with cars. For older and richer folks, assembling and making golf clubs and having fun on the course. Golf cart modifications are cool too.

@nerdyguy running that engine with only 1.5qts is a bad idea, even if it’s only for 5 minutes.

Why does he even feel it’s necessary to “flush” the crankcase? 99.99999999% of us don’t, and our engines are fine.

You may not be an eng’neer, but you gots a good head on your shoulders. - See more at:

I agree.

Yes, now that you’ve explained it, a TERRIBLE thing to do to an engine.

Some folks seem to think that old oil is dangerous, or poisonous, or somehow damaging to the engine, and that every (crazy) measure need be taken to get it ALL out at every oil change.

Which, of course, cannot be done. Unless one is willing to remove the pan and wash it out every oil change.

Bottm line, this is a fella whose heart is in the right place but his head is on backwards. I’m tellin’ you guys, we need more basic science (and/or critical thinking) in our primary and secondary schools!

I would no more put used oil in my engine than eat pre-eaten food!!

@Docnick - it’s crazier than that - the friend is draining ALL the oil, putting in just 1.5 quarts of fresh oil, running the engine, then draining the 1.5 quarts out and filling it up with 3.5 quarts of fresh oil.

“we need more basic science (and/or critical thinking) in our primary and secondary schools!”

Yes, we do need more of that type of instruction in our schools. On that, you and I agree.
However, the Republican Party in the great state of Texas disagrees with us.

This sounds like a bad joke, but their 2012 party platform included the statement that “higher order thinking” should be banned in Texas schools. I guess that the existence of higher order thinking would be in conflict with their science curriculum that teaches Texas kids that cavemen rode dinosaurs, and other Creationist nonsense.

Take a look at: