Lets talk about crankcase oil capacity

So, ive had an oil pan leak on the 3400 miata. Been a slow drip for a while, with a big puddle after the cruise night (30 miles of hot oil) on the shop floor. 

However, now its not leaking at all.

I had been putting the reccomended stock 4.5 quarts in it, despite having a large section of the sump cut out for crossmember clearance. It read roughly 1.5 quarts high on the dipstick. 

It now reads full on the dipstick, and is not leaking. Making me think that it may NOT be the welded pan leaking like ive thought. 

I have no idea how much oil by volune is still actually in the engine at this point. My guess is about 3 quarts. 

So, how do i determine how much this engine needs in this application? What are the plusses/minuses of oil level in the pan? Is therestuff im not thinking about in play? 

Because i am SERIOUSLY tempted to leave it the hell alone at the full mark on the dipstick to cure the oil leak. 

Any signs of oil starvation?  Can you put on a larger filter to increase the oil capacity?  I agree that ~3 quarts is the new pan level but I'd be worried about sucking air while running hard. Can't recall but you did baffles and stuff right?

The oil's top level is more important than its volume.  You don't want the crank to be whipping the oil into foam even more than it already does - that wastes power, and foam is not as good a lubricant as solid oil.  It also tends to expand the air when it gets into the crank and makes it way to the rods, or gets into hydraulic lifters.  If you thought 60psi of foam was bad, wait until you have a much lower pressure of mostly air.

If you want more capacity, make the pan deeper/wider.

Knurled. said:

The oil's top level is more important than its volume.  You don't want the crank to be whipping the oil into foam even more than it already does - that wastes power, and foam is not as good a lubricant as solid oil.  It also tends to expand the air when it gets into the crank and makes it way to the rods, or gets into hydraulic lifters.  If you thought 60psi of foam was bad, wait until you have a much lower pressure of mostly air.

 

If you want more capacity, make the pan deeper/wider.

QFT. Too high an oil level will kill an engine just as sure as no oil at all.

In reply to NickD :

You're a GM technician guy.  So you should know about the 6 speed autos that overheat and kill thrust bearings when they are overfilled by as little as 1/4".  And people wonder why everyone is going away from dipsticks in favor of check plugs.

Foam not only is a poor lubricant but it also doesn't transfer heat worth a damn.

In reply to Knurled. :

I've also seen dead 3500/3900s because Goober's Auto Repair does an oil change and thinks that a big V6 like that should take 5 or 6 quarts, instead of 4 quarts. 

Knurled. said:

The oil's top level is more important than its volume.  You don't want the crank to be whipping the oil into foam even more than it already does - that wastes power, and foam is not as good a lubricant as solid oil.  It also tends to expand the air when it gets into the crank and makes it way to the rods, or gets into hydraulic lifters.  If you thought 60psi of foam was bad, wait until you have a much lower pressure of mostly air.

 

If you want more capacity, make the pan deeper/wider.

This, with a wet sump setup you want to get as much oil in there as you can without having the crank run through it. Your oil level might actually be too high right now. The only downside inherent to a smaller oil volume is less oil heat capacity (edit: and for a street car, less oil contaminant capacity), if you have an oil cooler and can keep the oil from sloshing away from the pickup, go for it.

NickD said:

In reply to Knurled. :

I've also seen dead 3500/3900s because Goober's Auto Repair does an oil change and thinks that a big V6 like that should take 5 or 6 quarts, instead of 4 quarts. 

I just wish mine didn’t use a qt every 1000 miles....

Is the dipstick accurate with the altered oil pan?  Maybe drain the oil, and get an idea of how much oil is in there. Too much is no good, as stated.  Check out this calculator, it may help determine the capacity of the oil pan.  Perhaps an appropriately sized oil cooler?

https://www.sensorsone.com/length-width-and-height-to-volume-calculator/

The only real way to do it would be to get another oil pan, modify it exactly as this one, and then fill it with oil and note the capacity. The best part about this idea is you now have either an extra oil pan, or an item to sell to someone doing the same swap. 

So pretty much as long as its not overfull on the dipstick or starving at higher rpm as evidenced by the oil pressure gauge, its good. Right? Thats the way im reading this. 

After tge challenge it will get an oil cooler and such. 

You could always go back to pics of the pan cutting, and estimate the volume removed

edit: or that’s what I could do on the 14th.

also, is their Other evidence of where the oil is coming out... since it is leaving a puddle?

Dusterbd13-michael said:

So pretty much as long as its not overfull on the dipstick or starving at higher rpm as evidenced by the oil pressure gauge, its good. Right? Thats the way im reading this. 

After tge challenge it will get an oil cooler and such. 

I'd add not starving for oil under high G forces to this but, yes, that's essentially it. 

You could consider adding an Accusump to increase capacity.

I saw oil temps at 285 f when I over filled my 3400 by 1 qt.

So, over filled is bad.  However, still not sure how that would cause oil to leak.

In reply to wvumtnbkr :

Foam takes up more volume than solid oil.  Seals are also generally not meant to be flooded submerged, which is why they usually have slingers behind them to throw any oil out of the vicinity so they only have to hold back a trickle instead of a torrent.

My only thought is that it may have been leaking from the crossbolted mains due to oil level.

We cleaned the pan yesterday, drove it, and parked it iver clean floor. I will let it sit for a couple of days and reinspect. We saw no signs of oil starvation on the street at this time despite our best efforts to make it.

Knurled. said:

In reply to wvumtnbkr :

Foam takes up more volume than solid oil.  Seals are also generally not meant to be flooded submerged, which is why they usually have slingers behind them to throw any oil out of the vicinity so they only have to hold back a trickle instead of a torrent.

Agreed.  But, what seal would be leaking that looks like it's coming from the oil pan?

Front or rear main would be obvious I would think.

Also, did you put some sealant on the bolts that go to the cross bolted mains?  That was my guess.

In reply to wvumtnbkr :

Nope. Put them in dry.

That was a mistake  wasn't it?

Dusterbd13-michael said:

In reply to wvumtnbkr :

Nope. Put them in dry.

That was a mistake  wasn't it?

Not sure.  I put some rtv under the head of each one when I did mine.

As I rule I never put anything in dry. 

In reply to Crackers :

That's what she said!

Couldn't resist.

Think ill pull them out and seal them up on principle .