Correct Oil Level

Hi,

I've heard the "excess oil pressure" and "blowing seals" story for years, but have found little to support either of those ideas. The oil pressure's a function of what the pump design and check/relief valves allow with a given viscosity oil, modified by heat and engine wear among other things. Ever notice that there's little, if any, noticeable difference between the pressure with a full sump and one that's a quart/litre low?

OTOH, there IS a serious problem with overfilling that's pretty well documented. That's the problem of the oil level being high enough the crank spins around in the oil like an eggbeater and causes the oil to foam up. Now you're trying to pump aereated oil under pressure and it "collapses" because of the air, so you lose pressure and lubrication.

I don't know if one quart/litre is enough to cause this problem with a Subie engine. Usually a quarter to half qt/l won't make a bit of difference in most engines, but it's probably best to drain a little off in your case.

Rick

Check the level before you start the car for the day. This will give you an exact level... Does the manual state anything else about adding a quart if the filter is changed? IIRC, some manuals have two amounts, one without the filter change and one without

usually occurs on higher mileage or older engines where the seals are beginning to break down

I checked the oil after the car had been running so there would already be some amount of oil in the new filter. The manual clearly states that the notch is where the oil level may rise to when the engine is hot. It is not a maximum when the engine is cold.

-Todd

I agree, and in this case I would expect it to read somewhere between the low hole and the full hole, not anywhere near the notch, or in my case above the notch.

My manual doesn't say anything about adding an extra quart when doing an oil change. However in my case the car had been running so the oil filter would have had some in it.

-Todd

Not much if you use the cool trick I just learned - fill the new filter with oil before you screw it on (if, like on my engine, it installs gasket-up). Sigiificantly reduces that bad time when you first start the engine after an oil change and there's virtually no oil pressure.

John

Speaking of which, my '97 Legacy 2.5 seems to be leaking from the rear main seal (or possibly somewhere else nearby).

But I'm not losing much oil at all, and I'm sure it's a very expensive repair.

Is the fact that it's leaking SOME an indicator that a catastrophic failure is much more likely ? Or could I safely wait until the oil loss rate becomes more than a minor annoyance ?

Thanks, John

Hi,

In my experience, leaking front or rear main seals typically start to make a HUGE mess before they finally fail completely. A drop every few days is just a reminder to start saving your money, whereas a small puddle (1" or so?) every day says make the call and get your mechanic scheduled for the repair if you're not your own "wrench." A bigger puddle (2" or so???) every day says to me you should check your oil level religiously before driving until you get it fixed!

How expensive the repair is depends on what transmission you have, among other factors, cuz if you have a stick, leaking oil from a rear main seal will usually get on the clutch disc and call for replacement.

Rick

Double check your PCV valve and hoses. If it's not working well it'll increase/cause oil leaks.

Carl

John Eyles wrote:

Todd,

I had a similar experience when I took my 2002 Legacy GT in for its complementary 3000 mile oil service. When I checked the oil the next morning (cold engine), it was quite a ways _beyond_ the notch! I saw this as an opportunity to fill the crank case with the Mobil1 that I had recently obtained for a "song" at Wal Mart. Here are a couple of things to consider regarding "overfilled" sumps in these opposed engines, and in engines in general:

More oil != greater oil pressure. Oil pressure is a function of the oil pump, oil viscosity (temperature dependent), engine RPM, and bearing clearances (did I leave anything out?)

In some (many?) engine designs, overfilling the sump will allow the crankshaft webs to come in contact with the oil. This may or may not whip the oil into a foam. Foam does not pump well, nor does it lubricate well. On the Subaru engines, do to their opposed design, the crank shaft sits much higher above the oil in the sump, so you'd have to _really_ overfill for the webs to come in contact with the oil in the sump.

Happy motoring!

Oh yes, good idea, thanks. Haven't ever done anything with that stuff.

John

The tiny filter used on the Subaru engines can't possibly hold more than a cup of oil; it just doesn't enclose that much volume! I always put in 4 quarts (a bit less than 4 liters; 1 qt = .95 l), whether I change the filter or not. 5 liters seems a bit excessive, tho; I'd be tempted to take it back and make 'em do it again. But then they'd probably find a way to f___ something else up :-P

Todd, the dipstick on the subaru engines takes a bit of technique to get consistent readings. I like to take levels with the engine at operating temperature, but if you prefer to do it cold that's fine too, as long as you always do it that way.

The procedure that works well for me follows: Open hood and withdraw dipstick, wipe clean, and re-insert ~1/2 way. Wait a couple minutes (while fuel pumps or whatever). Insert stick all of the way, immediately withdraw and take reading.

If you subsequently re-insert the stick and pull without waiting, you will probably get a higher than normal reading. I assume that this is because withdrawing the dipstick pulls some oil up into the tube, which then finds its way onto the stick, confusing the level indication. Whatever, try the above procedure and see if it doesn't produce more consistent readings for you.

ByeBye! S.

Steve Jernigan KG0MB Laboratory Manager Microelectronics Research University of Colorado (719) 262-3101