Oil system myths
Thank you, YR. So it seems like the sump/pan is the culprit for most oiling issues.
^^^^^This is where I was going with my question. Perhaps cavitation was the wrong term, it's aeration that I was thinking of. Either way, lack of oil at the input of the pump is where the problems begin.
Oh I can think of a couple lololol
I agree with all of this and what Justin said in post 91. Im not disagreeing at all.
I know that when I sit down and figure out what I need for an oiling system, I figure pressure into it as well. At one point I was carrying 100 plus PSI and it made more power. That was with the same pump. I had an external bypass that was adjustable and on the dyno I kept increasing the pressure until the power went down.
And on that system I had blocked the bypass in the pump and used a line off the bypass to put the oil back in the pan in front of a baffle so it didn’t blow return oil back across the pickup and uncover it.
So yes, pressure goes hand in hand with flow, until the pump is producing enough flow to the point where the flow and pressure stays the same because the the system can’t use anymore oil and the bypass opens.
I hope that made sense. In my head it does, but when I read it back I’m it so sure.
The best example of this is using full groove mains and a standard volume pump. You will have lower oil pressure at idle because the rods are getting oil all the time. And that adds to the leaks at the rods.
So the standard volume pump doesn’t produce enough oil at idle and slower engine speeds to produce the same oil pressure because of the added flow loss to the rods.
At some point the standard volume pump will produce enough oil flow to open the bypass and that is the pressure maximum. Any more RPM (flow) increases don’t change the pressure because the bypass is open.
Take that same engine, with the same bypass relief pressure and add a high volume pump. The oil pressure will increase at idle and lower RPM because the pump is producing more oil at the same RPM because the rotors are taller, which equals more displacement.
At some point (earlier in RPM because the pump produces more flow at any given RPM with the HV pump verses the standard volume pump) the pump will produce enough oil that the system restricts flow to the point the pressure rises, until the relief opens and the pressure should stay the same regardless of RPM increase, again unless the bypass can’t flow enough and the pressure increases.
I guess IOW’s, the HV pump has more flow at a lower RPM than a standard pump so even with all the same parts and leaks the HV pump has more volume, thus more resistant and more pressure on the gauge until the bypass opens.
This is why I always say to use a HV pump on ANY Chrysler engine using full groove mains, or a solid roller cam with Chrysler oiling and a groove around the cam bearing(s) that feed the heads, because that extra system leakage requires more oil. And if you don’t give it the system suffers. And that’s usually at the end of the feed line. Which is the rockers.
You can have 20 pounds on the gauge and zero at the rockers (tested that). So I don’t like to see anything less than 40 at idle to keep oil flow to the rockers adequate. Unless it is bone stock or close to it.
As to adding oil and keeping the pressure up...that includes many other things.
One is application. On an OE engine, an extra quart of oil in each engine is burning money to the bean counters, so they are built with the lowest oil pan volume the engineers can slide by the nerds. Once you start to make changes to the engine AND/OR chassis, that pan becomes an issue. Increase the RPM and the engine WILL hold more oil.
So the issue isn’t the engine holding more oil, it’s the pan is wrong for the application. A stock pan is pretty much useless on anything but a stock engine. Start modifying the engine, use a bigger pan.
Since oil retention does go up with RPM, pan design, volume and windage trays and crank scrapers become much more important.
There are people running 4 or 5 quart systems on stuff shifting at 8k or more. But the pan is designed to do that, and they have trays and scrapers and baffling that would boggle the mind. And vacuum pumps. All that stuff matters.
Another factor that needs to be looked at is pickup to pan placement.
I can’t tell you how many Chrysler guys using a stock pans listen to the Chevy morons and put the stock pickup .250-.375 off the pan! That pan and pickup was designed to have an SLIGHT interference fit to the pan.
If you need a 1/2 inch impact to pull the pan down to the block you have too much interference. If you move the pickup away from the pan, it can’t pull the oil out of the pan and it will leave a quart or more in the pan. So you add a quart or two to make up for bad engine building.
Again, that is not a pump issue. That’s a pan issue.
Any engine running full groove mains and a stock pan is asking for trouble. The increased oil flow demand makes that stock pan questionable at best.
So I get what you’re saying about times when adding a quart of oil fixes an issue. I’m saying that’s not a pump problem, but a pan problem.
No serious engine should be built without adding capacity to the pan.
A stock pan is 4 quarts. A 6 quart pan is a 50% increase in pan volume. That’s huge. An 8 quart pan is a 100% increase in pan volume.
Increasing RPM or oil volume through the engine or both means you need more pan volume. If you don’t give the pan more volume, the first thing that suffers is the rockers. Run the RPM and the bearings will show you how pissed off they are.
Thank you, YR. So it seems like the sump/pan is the culprit for most oiling issues.
Here's another way to look at the oil system and the pan being "sucked dry".
If there is no oil available at the pickup tube there will be no oil flow. It doesn't matter how much oil the pump has the capacity to flow or how much resistance to flow the engine provides there must be oil available to the pump.
Can the pan be sucked dry? I'm not sure thats the right question. Can the pick up tube become uncovered? Yes.
I think what's being discussed are oil flow problems and there not happening idling in park. Oil demand changes in an engine when rpm changes and oil supply is affected by how we use the vehicle. From drag racing to rock climbing to circle track to road racing etc. We have to keep the pickup tube covered up with oil. Just look at the extreme measures that are taken in pan design , baffles, trap doors, oil capacity and etc. to accomplish this. So to answer the question "Can a pan be sucked dry?" I don't know. Can a pickup tube get uncovered? Yes, happens all the time. Is that cavitation? I don't know.
^^^^^This is where I was going with my question. Perhaps cavitation was the wrong term, it's aeration that I was thinking of. Either way, lack of oil at the input of the pump is where the problems begin.
25k+ elevation is a whole nother thing.
Very few people get that high.
Oh I can think of a couple lololol
