Can an extra oil quart cause a seal leak? Here's some facts -

I've seen it mentioned here and in other forums as well about an extra bit of oil (limit this to 1 quart over, and not more) and how it increases pressure on the seals, thus causing a leak.
Here are some facts ->

First:

The crankcase operates (normally) under a vacuum. The PCV is "Positive Crankcase Ventilation". In fact, one test for a PCV system is to use a vacuum gauge on the crankcase. It's so important to run negative pressure in the crankcase that engines used in drag racing where they have little to no vacuum to evacuate the crankcase use a vacuum pump to do the same thing. The higher the difference in pressure between the area above the piston rings and the area below them, the better the seal with many ring types.
This vacuum in the crankcase also prevents pressure from forcing oil out through gaskets, seals and so on.

Also:
The seals in our engines operate well above the oil level. They are never below the surface of the oil in the sump.

There is never pressure against the seals (although lip-type seals an handle around 7 psi or so, these don't have to handle pressure).
If there was some pressure, it would actually force the lip of the seal tighter against the shaft, improving the contact and sealing ability. Too much would wear the seal, of course.
But as crankcase pressure is removed via the PCV system, there is no concern.

In most engine designs, the oil from the main bearings is "slung off" and away from the seals by either a slinger, a washer type shape on the shaft between the main and the seal, or the crankshaft itself has a "slinger" machined onto it.
in the case of the 3.6, it's a large step up from the main bearing journal to the sealing surface, accomplishing the same effect - slinging oil away as the crankshaft spins.

Here is an example from my shop of a V8 crankshaft with the "slinger" for the rear main made as part of the crankshaft. Also note the machine marks - designed to "auger" oil back into the engine as the crankshaft spins. The pressure from the mains never gets close to the seal, no oil is "shot at it", it is slung away after leaving the main bearing area.



Below is a 3.6 crankshaft. Note the large step between the rear main (where the hole is) and the seal surface. That flat face acts as a slinger. The oil exiting the rear main is "slung away" by crankshaft rotation.
The rear main seal rides on the larger machined surface on the far left.
The seal is not exposed to oil pressure from the pressurized oiling system, and, oil is slung away from the seal as it leaves the rear main bearing area.


Here I show how the oil seal is never under oil, never submerged.
The image below is a 3.6 crankshaft.
Note the machined seal surface (where the bolts are on the right). That is where the seal "rides",




If you filled the crankcase to the point that the seal was operating in the oil instead of above it, look at what else would be in the oil.
Oil actually against the crank throws and counterweights would be a huge drag on the engine.
It would whip the oil into a froth. It would aerate the oil so bad, you'd lose oil pressure, the engine would be more noisy, lash adjusters couldn't take play out of the valve train. The rods and crankshaft throws, counterbalances, would be operating like a giant bakery mixer in the oil.
It would also take a lot more than 1 extra quart to get that far. The sump "size" increases as you move up. A quart of oil at the bottom will raise it x amount. Because the "diameter" of the sump increases moving upward, a quart of oil at the top will only raise it a small part of x.



Picture below -
The 3.6 has aluminum windage tray at the bottom to prevent the oil from being whipped into a frenzy by the spinning crankshaft throws and connecting rod ends dipping down and up like the wind on the ocean whips it in to a foam. Wind from the spinning parts can cause the surface of the oil to be 'foamed', aerated. Thus the windage tray.
(There are actually multiple purposed for the windage tray. It also reduces drag on the crankshaft as it spins, lowering "internal friction" or drag on the crankshaft. It increases the chances of oil releasing trapped air before being pulled back into the pump. )
If you added so much oil as to get above this tray, you are running the crankshaft in oil, foaming it up, losing oil pressure and losing protection of the engine parts. The drag on the crankshaft smacking the surface of the oil would be intense. You would reach destructive levels before the seal would be operating in oil.

This picture also shows an area that's a common problem area when people replace the rear main, and do certain other maintenance - the intersection of sealing surfaces.

I don't know what MOPAR recommends for sealer here - but no way I'd use RTV off the shelf, the generic stuff, and the amount 'gooping' out in this picture really concerns me........... I don't know who's engine I grabbed a picture of, but I'm glad it isn't mine they are working on.

The seal is never under oil.
Added oil doesn't put any pressure on the seals (crankcase operates in a partial vacuum, not pressure - they do NOT operate under pressure). Increasing the amount of oil can't increase oil pressure or put the seals under pressure. It's not a thing.



And finally - I am not suggesting people should run 6 quarts in the JL or JT version of the 3.6. I'm not saying anything like that.
However, it's not going to blow it up, either.

If I were operating at extreme angles in the rocks, I might add an extra half quart just to be sure the oil pump is never starved for oil at extreme angles.
I used to run 6 quarts in my 70 Javelin engine because so much oil stayed up to at high RPM and high speeds when you came to a fast slowdown at the end of a run, the oil light would flicker because the oil was up top, or thrown forward away from the oil pump pickup screen.

And when you start an engine, there's always some oil up inside that doesn't get back to the sump until after it's been shut down for a while (thus, the shut it off and wait a while before checking the oil level and adding any). That means a running engine isn't quite as "over-full" in the sump as an engine that's shut down. Running, you do not have 5 quarts in the pan, so to speak.

In other words - a little extra oil won't blow seals - but don't go testing to see just how much oil these can stand unless your name is Charles and you have permission to replace the engine anyway and don't care.

We know that when Jeep put the 5 quart version of the upgrade engine in the JL and the JT came out, many dealerships - perhaps others, were so used to "Wranglers with a 3.6 take 6 quarts" or "Grand Cherokees with the 3.6 take 6" that thousands of these were sent out the door with 6 quarts in them. And any Jeep owner who didn't do their own checking constantly probably drove until the next oil change was due with that oil in it.
That should be enough to show that 6 quarts doesn't blow seals.

Nice Bill!.....Jack

ShadowsPapa said:

I've seen it mentioned here and in other forums as well about an extra bit of oil (limit this to 1 quart over, and not more) and how it increases pressure on the seals, thus causing a leak.
Here are some facts, first:

The crankcase operates (normally) under a vacuum. The PCV is "Positive Crankcase Ventilation". In fact, one test for a PCV system is to use a vacuum gauge on the crankcase. It's so important to run negative pressure in the crankcase that engines used in drag racing where they have little to no vacuum to evacuate the crankcase use a vacuum pump to do the same thing. The higher the difference in pressure between the area above the piston rings and the area below them, the better the seal with many ring types.
This vacuum in the crankcase also prevents pressure from forcing oil out through gaskets, seals and so on.

The seals in our engines operate way above the oil level - way above. They are never below the surface of the oil in the sump.

There is never pressure against the seals (although lip-type seals an handle around 7 psi or so, these don't have to handle pressure).If there was some pressure, it would actually force the lip of the seal tighter against the shaft, improving the contact and sealing ability. Too much would wear the seal, of course.

In most engine designs, the oil from the main bearings is "slung off" and away from the seals by either a slinger, a washer type shape on the shaft between the main and the seal, or the crankshaft itself has a "slinger" machined onto it, or in the case of the 3.6, it's a large step up from the main to the sealing surface, accomplishing the same effect - slinging oil away as the crankshaft spins.

Here is an example from my shop of a V8 crankshaft with the "slinger" for the rear main made as part of the crankshaft. Also note the machine marks - designed to "auger" oil back into the engine as the crankshaft spins. The pressure from the mains never gets close to the seal, no oil is "shot at it", it is slung away after leaving the main bearing area.

Below is a 3.6 crankshaft. Note the large step between the rear main (where that hole is) and the seal surface. That flat face acts as a slinger. The oil exiting the rear main is "slung away" by crankshaft rotation.
The rear main seal rides on the larger machined surface on the far left.
The seal is not exposed to oil pressure, oil is slung away from the seal.

Here I show how the oil seal is never under oil, never submerged.
The image below is a 3.6 crankshaft.
Note the machined seal surface (where the bolts are on the right)

If you filled the crankcase to the point that the seal was operating in the oil instead of above it, look at what else would be in the oil. That would be a huge drag on the engine, and would whip the oil into a froth. It would aerate the oil so bad, you'd lose oil pressure, the engine would be more noisy. The rods and crankshaft throws, counterbalances, would be operating like a giant bakery mixer in the oil.
And it would take a lot more than 1 extra quart to get that far. The sump "size" increases as you move up. A quart of oil at the bottom will raise it x amount. Because the "diameter" of the sump increases moving upward, a quart of oil at the top will only raise it a small part of x.

Picture below -
The 3.6 has aluminum windage tray at the bottom to prevent the oil from being whipped into a frenzy by the spinning crankshaft throws and connecting rod ends dipping down and up like the wind on the ocean whips it in to a foam. Wind from the spinning parts can cause the surface of the oil to be foamed. Thus the windage tray.
If you added so much oil as to get above this tray, you are running the crankshaft in oil, foaming it up, losing oil pressure and losing protection of the engine parts.

This picture also shows an area that's a common problem area when people replace the rear main, and do certain other maintenance - the intersection of sealing surfaces.

I don't know what MOPAR recommends for sealer here - but no way I'd use RTV off the shelf, the generic stuff, and the amount gooping out in this picture really concerns me........... I don't know who's engine I grabbed a picture of, but glad it isn't mine they are working on.

Anyway, the seal is never under oil. Added oil doesn't put any pressure on the seals, they do NOT operate under pressure. Increasing the amount of oil can't increase pressure or put pressure on anything. It's not a thing.

And finally - I am not suggesting people should run 6 quarts in the JL or JT version of the 3.6. I'm not saying anything like that.
However, it's not going to blow it up, either.

If I were operating at extreme angles in the rocks, I might add an extra half quart just to be sure the oil pump is never starved for oil at extreme angles.
I used to run 6 quarts in my 70 Javelin engine because so much oil stayed up to at high RPM and high speeds when you came to a fast slowdown at the end of a run, the oil light would flicker because the oil was up top, or thrown forward away from the oil pump pickup screen.

And when you start an engine, there's always some oil up inside that doesn't get back to the sump until after it's been shut down for a while (thus, the shut it off and wait a while before checking the oil level and adding any). That means a running engine isn't quite as "over-full" in the sump as an engine that's shut down. Running, you do not have 5 quarts in the pan, so to speak.

In other words - a little extra oil won't blow seals - but don't go testing to see just how much oil these can stand unless your name is Charles and you have permission to replace the engine anyway and don't care.

We know that when Jeep put the 5 quart version of the upgrade engine in the JL and the JT came out, many dealerships - perhaps others, were so used to "Wranglers with a 3.6 take 6 quarts" or "Grand Cherokees with the 3.6 take 6" that thousands of these were sent out the door with 6 quarts in them. And any Jeep owner who didn't do their own checking constantly probably drove until the next oil change was due with that oil in it.
That should be enough to show that 6 quarts doesn't blow seals.

Click to expand...

Back in the day before the pcv, the crankcase was vented to the atmosphere. If you had bad rings, you would pressurize the crankcase and you could actually feel the pulsations on the oil fill tube. Now days, when you remove your oil cap the rpm could change and you may feel a little suction. Unless, your rings are not sealing. Then you may have enough crankcase pressure the the pcv can not handle and cause leaks. This engine is running rough and oil leaks are not the concern.

Talking about the crankshaft oil slinger. When I rebuilt my 283, I didn't have a rear main seal leak. I had an oul fogger problem. That thing smoked so bad, it was embarrassing to drive. Bought it like that, btw. The compression rings still did their job but the oil rings were carboned up severely. When pulling the rear main cap, the old rope seal was hard as a rock and cracked in several places, yet there was very little evidence of an oil leak. Slinger did it's job. I still have my rope seal tool that I never had to use.

Lost1wing said:

Back in the day before the pcv, the crankcase was vented to the atmosphere. If you had bad rings, you would pressurize the crankcase and you could actually feel the pulsations on the oil fill tube. Now days, when you remove your oil cap the rpm could change and you may feel a little suction. Unless, your rings are not sealing. Then you may have enough crankcase pressure the the pcv can not handle and cause leaks. This engine is running rough and oil leaks are not the concern.

Talking about the crankshaft oil slinger. When I rebuilt my 283, I didn't have a rear main seal leak. I had an oul fogger problem. That thing smoked so bad, it was embarrassing to drive. Bought it like that, btw. The compression rings still did their job but the oil rings were carboned up severely. When pulling the rear main cap, the old rope seal was hard as a rock and cracked in several places, yet there was very little evidence of an oil leak. Slinger did it's job. I still have my rope seal tool that I never had to use.

Click to expand...

Road draft tube, anyone? LOL

Yeah, the underside didn't rust so easily due to the oil vapors keeping the underside coated. Also sometimes left drips on the driveway

I have the tools for the rope seals.
The tool in the top of this picture is one used to shape the rope seal in a late 50s/early 60s AMC I6. It's roughly the size of the crankshaft seal surface.
I also have the Chinese finger puzzle type of devices used to pull seals through the seal channel when doing it with engine in the car. And the tools to rotate the upper bearing halves out of the place and the new ones in place when doing a bearing change - engine in car.

I talk quite a bit about the "slinger" for the rear main.
The front seal also has a slinger in place. You can see it here sitting on the block after I did the timing chain/sprocket install on a 4.0.

So there are slingers at both ends, doing the same thing. In the front, it typically slides over the nose of the crankshaft. Oil is slung away from the seal, there is no pressure at all on the seal and it doesn't ever run in oil. It would have to be grossly overfilled to the tune of several quarts.

ShadowsPapa said:

Road draft tube, anyone? LOL

Yeah, the underside didn't rust so easily due to the oil vapors keeping the underside coated. Also sometimes left drips on the driveway

I have the tools for the rope seals.
The tool in the top of this picture is one used to shape the rope seal in a late 50s/early 60s AMC I6. It's roughly the size of the crankshaft seal surface.
I also have the Chinese finger puzzle type of devices used to pull seals through the seal channel when doing it with engine in the car. And the tools to rotate the upper bearing halves out of the place and the new ones in place when doing a bearing change - engine in car.

Click to expand...

I'd soak the seals over night after my first failure. I was 14 or 15 putting a rope seal in. Put it in dry and got it perfectly flush! Yeah, that didn't work out all.

Nice writeup.

That pressure has to go somewhere.. yea. Good by seals

Sot said:

That pressure has to go somewhere.. yea. Good by seals

Click to expand...

I guess you didn't read it. There is no pressure.
Challenge for you - explain WHAT pressure you are talking about, show it, diagram it, explain where it comes from.
(reading comprehension simply seems to escape some - or like another post - he's just trolling)

With my Corvette C5 Z06 came an instruction video where they stated to add a quart of oil when taking the car to the race track.

Nice write up on sealing. The cast aluminum windage tray in the 3.6 also serves as a block stiffener, for the same reasons that the old 4.0 liter had the stamped stiffener on the main caps.

I remember road draft tubes. Probably the best that could be hoped for is to prevent pressure build up in the crankcase. This required that the crankcase breather allow air into the crankcase. The engine crankcase is not pressurized unless there is a problem with ring sealing or a major overfilling of oil (enough to cause the crank throws to whip up the oil.

As for sealer on the Pentastar, I always use Mopar Threebond RTV. That looks like a mess on the one in the picture, but after the bolts are torqued on the seal plate, the excess should be cut off with a razor blade. If the Threebond is used as instructed, it will seal for the life of the engine.

Charles 236 said:

As for sealer on the Pentastar, I always use Mopar Threebond RTV. That looks like a mess on the one in the picture, but after the bolts are torqued on the seal plate, the excess should be cut off with a razor blade. If the Threebond is used as instructed, it will seal for the life of the engine.

Click to expand...

My fear is more "what's inside, under the plate" to break off and get into the engine. Even years ago you needed to seal around the rear main cap and so on, and trimmed excesses, but I've seen it to the point where the RTV squeezed out away from the sealing surfaces and literally broke off - into the engine.
For me - a thin layer that can't ooze out, and enough at the intersection you can razor blade a nice flat seal area.

Charles 236 said:

The engine crankcase is not pressurized unless there is a problem with ring sealing or a major overfilling of oil (enough to cause the crank throws to whip up the oil.

Click to expand...

Yes, exactly.
That's why I limited it to 1 quart over, or a little over, not multiple quarts.
Oil so full it gets whipped into a nice meringue, you will likely suffer damage beyond a seal.
If there's a problem with ring sealing, main seals are the least of their worries!

Oil_Udder on BITOG was on the design team with the Gen 1 Pentastar. He said all Chrysler/FCA engines....and this one was designed during that time, had to meet all performance standards either overfilled by 1 quart or at up to 1 quart low.

Everything Bill said and showed would easily support that.

And, as Bill mentioned, how many hundreds of thousands of even millions of these have been overfilled to 6 quarts by dealerships? We've seen so many of those, as has the JL forum.

One more thing not to worry about!

Thanks, Bill!

DanW said:

Oil_Udder on BITOG was on the design team with the Gen 1 Pentastar. He said all Chrysler/FCA engines....and this one was designed during that time, had to meet all performance standards either overfilled by 1 quart or at up to 1 quart low.

Click to expand...

Now I recall you stating that elsewhere, forgot about that, though. But it's still easy to see just in the engine design itself - parts placements and more.

ShadowsPapa said:

My fear is more "what's inside, under the plate" to break off and get into the engine. Even years ago you needed to seal around the rear main cap and so on, and trimmed excesses, but I've seen it to the point where the RTV squeezed out away from the sealing surfaces and literally broke off - into the engine.
For me - a thin layer that can't ooze out, and enough at the intersection you can razor blade a nice flat seal.

Click to expand...

Exactly. Back when RTV first showed up around here, it wasn't uncommon to pull an oil pan and find the oil strainer full of what we called "blue goo". I pulled intake manifold off off big block Chryslers that the shade tree mechanic had "sealed" the gasket on by coating it with RTV, resulting in a sticky mess. At least with Threebond RTV, I have never seen it break loose and get into the strainer, but it is much stronger than parts store RTV. Incidentally, the RTV in the picture of the rear seal above is not Threebond, which is a light gray when set up. It appears to be Mopar Engine Sealer RTV, which appears dark gray to almost black when set up, but this is based on the colors I'm seeing.