I see no benefit to using “used” oil to top off the oil in your vehicle. I guess it depends on whether you think it is worth the gamble. No car manual would ever suggest that and there’s a good reason for it. If you’re replacing oil, the idea is not to add more pollutants but to add clean oil to dilute whatever pollutants already exist.
I’m sure someone will come along now and claim to have driven a gazillion miles using only “old” oil and having no problems whatsoever with their vehicle.
Think of it this way… If you had used new oil in that same car you probably would have driven 2 gazillion miles without any problems.
If the argument that oil is good for 10k miles (synthetic or not) then the synthetic oil that was drained at 5k miles should be perfectly fine for anothe 5k miles according to that logic.
Swapping it from one car to another should not be an issue.
Note that I’m not in favor of this practice; only wondering why draining it prematurely according to the above logic would cause the oil to become inferior suddenly.
I recall my grandfather telling of when he was a child how the family brought in water from the well and heated it on the stove in buckets and filled a large wash tub. The family of 5 took their turn bathing on Saturday nights. Certainly that bath water was dirty when the 5th finished but was it clean when the 5th began? Maybe the oil drained at 5,000 miles is pristine. Maybe not. To each his own.
On a car in good condition with an engine that’s in good mechanical condition other than leaks I’d say use new oil although adding used oil probably wouldn’t hurt anything. I’ve been using used oil in my '88 Escort for topping off oil for probably the past 100K+ miles, but the body/interior are in poor condition and the engine has 518,700 miles and uses/leaks a quart about every 800/1000 miles and not worth doing a rebuild or repairing major leaks. Used oil would be better than no oils in case of an emergency, but you’re also flirting with chances of running into sludge problems. On my other cars I change oil every 3/5K miles and add new oil when needed so this is what I use for topping off oil. Maybe if you’re within 500 of an oil change adding strained used oil just to get you to an oil change would probably be OK as long as the used oil didn’t already have 8-10K miles on it. Straining the oil isn’t going to remove all the contaminants in the oil, but will remove any large particles that may have got introduced while draining it from the car on a previous occasion. Only you can determine the condition and value of your car and make the decision. I started using used oil for topping off when my Escort started going through a quart every 1/1.2K miles and the engine had approximately 400K miles on it. I had to remove the oil pan about 1 1/2 years ago and clean the oil pump pick up screen because of low oil pressure. The low oil pressure was caused by sludge in the engine probably partially caused by the used oil and partially from the car being driven to work on dusty construction sites for the first 12 years/350K miles of it’s life.
If instead of a tub, they would have used a modified flower sprinkler as a shower, they all could have bathed in fresh water instead. I’m for fresh water and fresh oil. I just can’t see how someone could stand to pour used oil in their engine.
RE: Rod Knox story about bathing once a week in a tub.
My mother also grew up that way. With five children in her family, once a week they would fetch water from the well, heat it up and bath in a tub in the living room. My 98 year old aunt still lives in that house.
Re bathing… We all take a great deal for granted these days. My grandfather’s old homestead is just a pasture today but when I was young the old house was still standing. You could see daylight through the spaces in the wall boards and feed the chickens through the cracks in the floor. And today, most of the world would be grateful if they could live like my grandfather did in 1900. We in America should all be very thankful.
I think it pays to be optimistic. Sure it could be one of the engine’s main dynamic oil seals. But sometimes the oil drain bolt – you know, the thing you take out when you change the oil – that will leak a bit, but the oil blows back to the pan bolts when driving, so it appears like the pan is leaking instead. You might try putting a new rubber or cork gasket on that next time you change the oil. I’m not recommending it, but me, I make my own gasket for this out of an old inner tube, and it has worked ok for me so far.
Yes, GSJ, the drain on many late models requires a good seal ring. I prefer the soft copper washers but the plastic version is much cheaper and most parts stores stock them.
If oil would be good to 10,000 miles, and is drained at 5,000 miles, it very clearly will run for another 5,000 miles. To say differently, really stretches my imagination.
The only thing, change the oil of that leaker at the usual correct time. Bad stuff accumulates in the engine even if you are leaking a lot.