Cars: Oil leak = No replacing filter?

If you have a “quart a week” oil leak… IMO you don’t need to change your oil. But, do you have to change the oil filter?

My first guess was no, because you always have fresh oil in there. But, then I thought about it and was wondering if the specs of metal that the filter filters out leak out along with the oil, or if the specs of metal are too big to fit through the small leak and stay in the system, further clogging the filter?


Well, the filter will trap more stuff than the leak, because if the leak trapped stuff, the stuff would eventually plug the leak, eventually keeping all stuff in circualtion after that.

All stuff isn’t getting passed by the leaky area and dripped out on all passes, so the filter is still gunking up with whatever gunked it up before? Got that? The filter takes the stuff out on it’s first go around, whereas the leak wouldn’t, even assuming the leak could.

No. Not because of any oil quality considerations but because the engine isn’t worth an oil filter. If it was, it would be worth fixing the leak.

If you don’t change the filter, it could eventually clog. The bypass valve will pop open and you’ll have unfiltered oil pumping through the engine. There’s a risk that this will cause premature engine wear.

When you run out of oil (which will eventually happen), you’re going to throw a rod or face other severe engine damage.

If you’re going to risk catastrophic engine failure, it seems silly to worry about premature wear.

Assuming I have this leak in the OP, how am I going to run out of oil if I check it everyday and never drive very far and look at the ground after I pull out of every parking spot/driveway?

Fix that leak!!

The leak does not filter all particles, even if particles are escaping via the leak. Many are being left behind and caught by the filter…indefinitely until you change it or it clogs.

Maybe the leak causes a minor minor reduction in the particles caught by the filter, but it is likely insignificant and not worth any change in service habits. Most particles go right past the leak, leaving your filter to deal with them.

I can not see how the burden on the filter had been eased by any measurable amount if you have a leak.

Let’s say the crankcase holds 4 quarts. In a given week, you lose 1/4 of your oil, and 1/4 of the acids and other non-filterable contaminants that build up in it. Adding fresh oil does not make those contaminants disappear. So, compared to engines that don’t leak, this one has 75% as much acids etc.

Change the oil and the filter.

If I read your post correctly then everyone else misinterpreted it. You suggest not changing your oil, but adding a quart a time as needed but still changing your oil filter at intervals.

If this is correct I disagree with this being a good idea. Changing oil doesn’t just remove particals and contaminants the filter doesn’t catch but it replaces oil broken down by heat. Remember that not all contaminants are particles. Puttingin a fresh quart dilutes them somewhat but never gets them out of the engine. Change your oil even if you have a leak.

GaryT: You just said “you lose… contaminants.” Then you said that “those contaminants [don’t] disappear”. I don’t understand.

What does it matter if the oil comes out the plug or a leak… it’s still an “oil change”. Can you tell me the difference?

Have you ever seen the difference between fresh oil and oil after only 1,000 miles? (Of course you have) Just by touching it, I can tell it provides better lubrication. I’ll be happy to deal with a leak if it means I can have a constant supply of fresh oil to lube my motor… wouldn’t you?

You lose the junk in the oil that leaks out. However, the majority of the oil, and the junk that is in it, stays in there. My point is that even though the leak dispenses with some of the contaminants, most of them are still in there degrading your engine.


The difference is getting all the contaminants out and having a significant amount of running time with ALL fresh, clean oil. Your system subjects lubricated parts to more exposure to acids, etc.


That fresh oil doesn’t feel so good after it’s mixed with several quarts of dirty oil. And the point is, it’s not just a matter of getting fresh oil in, it’s also a matter of getting dirty oil out.

You could be the one driver out of a hundred that can keep this engine topped up. For the rest of us, it isn’t going to happen. The roommate is going to borrow the car, or someone will forget to pick up oil at the store, or checking the oil will get put off “just for a day” due to weather/sleeping in/finals week/whatever.

I’ve seen plenty of cars with moderate oil or water leaks. I’ve yet to see a driver–including myself–who could keep up with the leak for more than a few months.

Just out of curiousity, is the OP a hypothetical question? If not, what condition is the rest of your MG?

Also, please remember that you are dumping a quart of oil a week all over city streets, parking lots, other people’s driveways, etc. You’re crapping where you live.

You have a responsibility as a citizen to get your damned car fixed. Or don’t drive it.

I agree with Sam Stone As far as the need to change your filter, does the oil on the dipstick look like clean oil, or is it dirty?

The issue is the filter is still getting clogged at darn near the same rate.

Oil ‘looks dirty’ because it changes in appearance, so fresh looking oil is quite deceotive as far as the filter goes. The filter is still getting clogged, and fouling the other oil, or kncking down the pressure, retainging harmful by products/acids, etc.

Actually, you are setting yourself up for further leaks, because all the gunk and acids you aren’t fully flushing out are the very things that eat away at gaskets.

Gasket leak main culprit: poor oil/filter change habits. The crap stuck in the filter is harnful.

If I can attempt to illustrate GaryTs point…

Take a full glass of water…this is the clean engine with clean oil. After drving if for some time contaminants will build up in the engine oil. Put a couple drops of lemon juice in the water. You can see the slight difference but it’s not too bad. Now pour out 1/4 of the water and add new stuff. Put another bit of lemon juice in the water and empty out 1/4 and add new water. Continue on for however long you’ve been doing this for your car. The water will still have some colour to it no matter how many times you pour some out and add new. If you want the water to be plain again, then you’ll have to dump all the water and start fresh.

Very True. But weigh that against the argument that adding oil every week will ensure the car never runs with completely crappy oil before the scheduled oil change. Which is worse? Having sub-par oil all the time or having really bad oil some of the time?

But, I do agree about how not all the specs and acids leak out. I do agree that the best thing to do is change it, of course. Just, maybe not as often. :slight_smile:

I changed my filter.

My first car had a leak around the bearing. The guy at the shop told me that he’d have to take out the engine to fix it, and it would cost $400. After a pause, he said “$400 will buy a lotta oil.” I took his point. Besides, as a Starving Student I didn’t really have much coice. So I topped off the oil frequently, but I also changed the filter at regular intervals. And it did get dirty.