Oil level drops after car sits

[TallPaul]

Every car I ever had, the oil level on the stick rises a bit after the car sits for a long time. This was due to (so I would assume) the oil draining down into the pan from the top end.

In my 1999 Plymouth Voyager the 2.4L 4-banger does the opposite. For example, last night we had a long run and about 5 minutes after we shut it off, I checked the oil. It was about 1/4-inch above the full mark. I checked it again in about 2 hours and it was about 1/8-inch below the full mark. Again this morning (about 14 hours later) it was 1/4 inch below the full mark.

So from hot to stone cold (about 55 F overnight), it had about 1/2-inch lower reading. Also, it is not leaking out of the engine.

The question I have is, what is going on? Why, if the oil drains down from the top end over time, would the level in the pan decrease?

This is not a problem, just a curiosity to me.

 

[Food Scientist]

Oil shrinking as it cools?

 

[AKhan87]

the level should increase as it's sitting overnight, in your case, your engine is burning oil while it's turned off, that is the ONLY explanation and no other if it's not leaking.

LOL.

 

[Eddie]

My Subaru had two top oil levels. One for HOT and one for normal running. Oil and Aluminum expands when hot which explains it.

 

[toneydoc]

I would drive the car to full operating hot temps which will take 15-20 min or so and recheck the oil level. If it is again up on the stick, then you have increased oil level due to the heating of the oil. Then check it again when cool to verify decreased level.

My Harley has two levels on dipstick. One for cold level and one for hot operating temp level.

 

[berniedd]

Do you wipe the dipstick with a rag or tissue before reinserting it into the tube before taking the reading?

 

[TallPaul]

Oh yes, I wipe the stick every time. You ought to drag up my old thread from about 10 years ago titled something like, "What do you wipe your dipstick with." That thread really got some mileage.

Yeah, I don't think the oil can expand that much with heat. Some metal part expanding maybe could intrude into the cpacity but that much?

Maybe the location where the stick goes is a small chamber off to the side of the main pan?

 

[supton]

Is the dipstick on a straight shot to the pan? I wonder if it oil on the tube causing false high reading when hot.

 

[TallPaul]

Yes, the dipstick goes pretty much straight down, maybe on a 15 degree angle off from verticle with a slight bend to vertical near the upper end. I don't think it is an false reading because is not spotty but solid oil ending abruptly. And with 4000 miles on the oil it is nice an black and easy to see.

 

[Spector]

My experience is that oil does expand some when hot so the cold readings are always lower for me (even after waiting overnight for more oil to drain back down), at least on my vehicles.

 

[Lapham3]

Sometimes magic happens. The wife's Jeep magically stopped it's small rear main seal drip last year after many years of drips and using the same oil. My old Fiero will slowly drip a bit from the pan constantly as it may sit for weeks/months-but not from the drain bolt-all 4 quarts should be contained in the pan-but no cracks or impacts to the pan. So a leak from above that keeps on going. Who knows these things!

 

[TallPaul]

This puzzle was never solved. Just changed the oil last night. Added the specified 4.5 qts with filter change. Ran it, shut down, waited 5 minutes. Oil read at the full mark.

Next morning oil reads about middle of the save zone, or roughly 1/2 qt low.

In all the cars I have ever owned, they always read higher on the stick after the car sits a long time because of the oil draining down in the engine.

Gotta be something really weird going on here. Oh well. It runs well and ain't burning oil or blowing up.

 

[Doog]

Q: What does the manufacturer recommend check it cold or hot?

 

[lubricatosaurus]

Originally Posted By: SVTCobra
Oil shrinking as it cools?


Oil in a 5-quart sump shrinks in volume by about 1/4 quart, given the coefficient of expansion of 0.00039/degF and observations too. (The coef of expansion for steel or Al oil pans would be negligible, a couple of orders of magnitude less, like "noise".)

 

[WobblyElvis]

How about... air bubbles are rising out of the oil and reducing it's volume?

Fuel or water in the oil that is rising and evaporating out of the oil?

 

[supton]

Originally Posted By: WobblyElvis
How about... air bubbles are rising out of the oil and reducing it's volume?

Fuel or water in the oil that is rising and evaporating out of the oil?


Hmm, air trapped beneath the oil? Pretty big air bubbles I'd think. Seems plausible though. Maybe the oil level is actually too high in this case?

 

[TallPaul]

mfr says check hot, so i do and if shows half low cold I wait until hot to check it.

 

[Ohle_Manezzini]

That^^ and also Maybe the sump baffle is touching the dipstick and feeding the level line for a while.