Why does less oil come out than goes in?

[TallPaul]

Okay, I just drained the Aerostar 3.0 Vulcan V6 (1992). It was at the bottom of the safe zone and between the crankcase and filter, I got 3.25 quarts. I installed a new filter and filled it with 4.5 qts, which put the level right in the middle of the safe zone, which is half a quart above where it was when I drained it. So 4.5 - 0.5 is 4 qts to the bottom of the safe zone, but it was at that level and only 3.25 qts came out. Where did the other 0.75 qts go?

The filter holds about 0.75 qts, but I drained it. Sure the oil was not as hot (ran 18 minutes in driveway on 20F day), but I know a lot of oil came out of the filter, at most 0.25 qts is left in the filter and likely much less. Also I did not use a larger filter. So we have at least half a quart that is unaccounted for. No, it's not left in the pan, I drained it well. Nor is it on the floor as I did not spill it.

Not just this oil change, but typically every oil change I get significantly less oil out than I refill with, even accounting for different levels before and after the change.

 

[GMBoy]

I'd say its still in the oil gallerys of the engine as well as some puddling under the valve covers and then a little in the pan that is below the drain plug hole. Plus, even though you drained the filter, like you said, there is still some oil soaked in the pleats. Some oil may even be in the oil pump assy. That seems like it would all total almost a qt.

 

[Eddie]

To get a really good comparison I would get some one gallon empty bottles (milk bottles). Drain the used oil & empty the filter into one and mark the level. Prefill the new filter and dump it into the new bottle and then fill with new oil to the same level as the drained oil. Fill the engine with the new oil bottle.Then check the level after running the engine for 5+Miles and wait 10+ minutes before checking the oil level. That is what I do with a plug drain/refill of my AT. Let us know your results and if needed we will make a REAL research project of "where did the oil go".

 

[SamSpade]

My best guess would be the oil pan is shaped in a way that it tapers upwards especially above the dipstick safe zone. If that was the case the dipstick wouldn't give a linear reading of the oil. The same 0.5" below the safe zone would correspond to a larger volume than the same 0.5" above it.

Something like this:

__|...|...|___
|......|.......|
|...............|
|...............|
|...............|

 

[TallPaul]

I used a one gallon container, marked in half quarts, for the waste oil. I have mircomanaged the safe zone. It has 12 diamonds up the middle of the hatchure markings. Each diamond is approx 3 oz, but the end ones are cut off so are about 2 oz. It is pretty linear. Still, it would be better to put in the exact amount it should take to get to the previous level, that is, I should have only put in 4 qts until I checked it.

Also, I did run the engine about 17 mile and waited a long time, then checked the level. Any oil left behind would limit the refill capacity, so I don't see where that matters.

 

[aaxb970]

In the nooks and crannies?

 

[jldcol]

Your level difference may mainly come from how much oil actually goes into the filter, and if your estimate of .75 qts is accurate. what I do on a new/different can is refill the pan quart by quart, checking the level on dipstick so I know if it's accurate/to calibrate it, and when it's full replace the filter empty and start the engine. Let it run a few min. and then see how much it drops, and since you just calibrated the dipstick you should get a accurate reading. The other posts mentioned other places oil can hide allready.

 

[GMFan]

When you drained the filter, did you just dump it into the pan or actually puncture a hole in the metal and then drain it? There is A LOT of oil between the inside pleats and the outer filter wall. Simply tipping it over while intact only gets a little bit of it out.

 

[TallPaul]

I always run a screw up one of the antidrainback valve holes, then set it in a funnel with that hole at the lowest position. A lot comes out.

I wonder if BITOG member, Idrinkmotoroil, came by and sipped at my drain pan while I was busy getting the new oil from the house?