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572 BBC - 70psi up to 4500rpm then Drops to 20psi...?

RiverJeff

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Ok guys who can help with this one.

Ive got a 572 Big Block Chevy in a jet boat with a weird high rpm oil issue. The engine makes 40psi hot idle, holds a steady 65-70psi up to 4500 rpm but then anything over 4600-5000rpm and the oil pressure immediately drops to ~20psi.

The drop happens right away over 4500 rpm and the pressure shoots back to 65-70psi when you lower rpm back to 4000-4500psi. It does get some air bubbles on the stick after the run but with how fast the pressure comes back I feel like the air is a symptom not the cause.

Anyone know where to look?

Here is the set up:
-Bowtie Chevrolet Block (OEM drainage)
-Merlin Cast Iron Heads (OEM drainage)
-Milodon 10qt pan with full windage tray (I've run 5,7,10qts & same issue)
-Milodon pick up bolted to pump
-Melling HV77 pump - new
-Pink pressure relief spring - 70psi
-Solid lifters with .060" restrictors
-Pressures verified with mechanical gauges
 

69hondo

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I am no expert but what generation block, Sounds like you are blowing the bypass plug out.
 

Instigator

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sounds like the pump is sucking the pan dry for 1 reason or another.
 

mjc

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I had this happen on a SBC, too much oil going up into the heads and can't flow back fast enough. clean up the head casting and maybe the oil restricter is still to big.
 

wet hull

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Feel you on oil Gremlins. Mine runs high. Mechanics have checked everything and zero issues in 8 yrs. Runs about 90-100psi. On a hard pull it drops down to around 80psi. Kinda wondering if the ohms on my gauge don't match sensor. Good luck
 

DaveH

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Feel you on oil Gremlins. Mine runs high. Mechanics have checked everything and zero issues in 8 yrs. Runs about 90-100psi. On a hard pull it drops down to around 80psi. Kinda wondering if the ohms on my gauge don't match sensor. Good luck
ive seen this before.

wont be an issue with a two wire sensor, only single.

if someone got overly happy with teflon tape on the threads, or there is an anodized thread adapter....the sensor doesnt get a good ground.

if you have a multi-meter...test resistance from the body of the sensor to battery negative. it should basically be a dead short. any resistance will throw off the gauge.

obviously if you have the wrong sender then that needs to be addressed.
 
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welldigger00

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I think that all the oil is in the top end as well. Mine will heat the oil up on hard pulls under boost, but only drops to 50


Sent from my iPhone using Tapatalk
 

BamBam

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While I think it could be possible, like the others have said, to have all of the oil in the top end, I do not believe that is your problem. You stated you get the same results with 5, 7 to 10 quarts in the pan. I am thinking that your pump pick-up may be too close to the pan. As RPM increases the oil pump continues to spin faster and draw in more oil. The only thing that keeps the pressure in check and not continuing to climb with RPM, is the bypass spring which dumps excess pressure right back into the pan. Oil pumps are positive displacement pumps and volume increases with RPM. The system reaches it's max desired pressure in a low RPM range and the pressure is then regulated by the spring keeping it from increasing on the "out" side. The "in" side of the pump will continue to suck more and more. If that suction is enough to close the gap between the pick-up and the pan you could have a drop in pressure at that RPM. As you state it is like a switch at 4500 RPM. That's only one guys theory but could be your problem. Hope you can solve the problem and enjoy your boat soon.
 

Eliminator21vdrive

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So I have heard that Milidon pickups can be restrictive due to design = perforated metal rather than screen
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RiverJeff

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First off thank you all very helpful responses.

So responding to the block it is a Gen4 block with no bypass. Canton Racing adapter: https://www.cantonracingproducts.co...te-oil-filter-adapter-sbc-bbc-straight-ports/

As for too much oil heading up top I haven't seen a change with adding or subtracting the oil. A 10qt pan, no restrictions in block drains or heads should be plenty to drain back.

DaveH, I verified with 2 mechanical gauges (one at pump one at end of lifter gallery) however I had heard this issue with the electrical gauge before.

BamBam, I checked the pan to pickup clearance when I put the new pump and pick up in June. The clearance is ~0.595" (actually a bit more than this ±0.020). I don't think you would want to go too much further than that. Thoughts?

You started taking about the internal pump bypass/spring pressure. I put the MEL-77070 purple 70psi spring in the pump. This is a line of thinking I was going down as well. If the pressure was too high and it blows the valve open shouldn't it just open enough to pull the pressure down to 70psi?

I am running 20w-50 oil, is there a possibility that at the +4500rpm the pump is trying to push too much volume for the bypass orifice? Is the "thick" oil so thick that even with the pressure spring open it doesn't flow enough so that the pump gears are actually cavitating? Would running thinner oil solve this problem?
 

Mcchevy69ss

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Does the pressure drop immediately once it hits 4500 or slowly fall off? If it’s immediate, I think it’s a pump related issue. If it holds for a while and then falls off, it is probably oil drain back or aeration issue. Was the pickup welded to the pump?
 

RiverJeff

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I had this happen on a SBC, too much oil going up into the heads and can't flow back fast enough. clean up the head casting and maybe the oil restricter is still to big.

Do you or anyone have experience with this problem? I’m wondering if the cam/lifter upgrade could be causing this issue.

I’m running Isky roller lifters and their cam with the .060” restrictors. This seems pretty small I don’t think you want to run much smaller?

Anyone have pressure loss at high rpm with solid lifter setup?
 

RiverJeff

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I spoke with Milodon’s tech and we are thinking this may be a pump cavitation issue.

I am going to try a Melling 10778C. This comes with the anti-cavitation plate. It’s high volume standard pressure.
 

Streetmoto

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When the oil pressure drops to around 20, is it steady or jumping around? I would think if the pump is sucking the pan dry the pressure would be jumping around, spiking high and low as some oil returned to the pan. I think the fact that it happens at the same RPM regardless of the amount of oil in motor also tells me it's probably not sucking the oil pan dry. I'm guessing it would require pulling the motor which is a pain but I'd probably try swapping out the oil pump. Good luck!
 

Mcchevy69ss

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It is not likely a cavitation issue at 4500 rpm... we have spun stock pumps well beyond 7k without this issue. Be careful with the pump they are trying to sell you, they don’t perform well at lower RPM.
 

Moneypit

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It is not likely a cavitation issue at 4500 rpm... we have spun stock pumps well beyond 7k without this issue. Be careful with the pump they are trying to sell you, they don’t perform well at lower RPM.

Yes, that pump is not made for idling, it is a balls out type pump..IMO, it is that non by pass adapter... Put a remote adapter that spins onto the factory by pass filter spin on mount... If you said what oil filter you are running I missed it, but the filter should also have a by pass built into it... 70 psi is waaay to much oil pressure. Where are you reading the pressure from... Before or after the filter??

IMO the pressure should top out at about 45-55 MAX. Pressure restrictions, like non by pass components, could run the pressure up until the filter gasket fails... Those Melling performance pumps are killer, but they're also touchy as to their application. Before you change anything inside the pan, change all the non by passed components to those with built in by passes... The remote adapter, use one that spins on to the stock factory by pass filter adapter, or an aftermarket adapter with a by pass, and use a filter with a by pass... Fram PH 13, or performance, what is that a PH4.... NOT WIX RACING.....
Your "4500 switch" could be max non by pass filter flow rate... Try allowing the filter to by pass oil into use above the 4500... Try it before you pull the pan...
Ray
 

Moneypit

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Yes....70 is on the very high end... Think about it, pressure is "back pressure", some sort of restriction in the system... Rod side clearance comes to mind, and if the oil stays in the bearings too long it gets too hot to do it's job... 50# at WOT is plenty, 25-30 at idle....20-50 or 50 wt racing....70# is eating horsepower...
Ray
 

wettrthebettr

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.20-50 or 50 wt racing....70# is eating horsepower...
Ray
I always was told that 20-50wt oils had 20wt when cold and 50wt when hot, I just put my resto back together and only made one short test run, but the lake and ambient temp is cold now . My test run was pretty short without the engine cover and all the upholstery, so I could see everything, I'll know better the next run on a bigger lake so Engine can get to running Temp, but the water will be cold.
 

Moneypit

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I always was told that 20-50wt oils had 20wt when cold and 50wt when hot, I just put my resto back together and only made one short test run, but the lake and ambient temp is cold now . My test run was pretty short without the engine cover and all the upholstery, so I could see everything, I'll know better the next run on a bigger lake so Engine can get to running Temp, but the water will be cold.

Yes, 20-50 oil is fine... Especially in cold water climates... A simple example of how higher oil pressure robs net horsepower is a common drill motor while spinning up the pump to prime the system before initial start up... You can watch the pressure come up as the system fills, and hear/feel the drill motor bog down against the excessive pressure.. The Chevys run some pretty stout oil pressure drive shafts and there are even the aftermarket super strong ones available with the steel collar replacing the plastic one that the stockers use... Mellings makes pumps for high volume, as well as high pressure, and supplies different relief springs to further "dial in" the pump to the application. Care must be taken when using the various pumps because a high volume pump can really drive the pressure high simply because of the engine oil system being "tight", and a lower bypass spring/setting may not have the "flow" required to drop the overal pressure down to acceptable levels.. Yes, oil kept in the bearings too long can overheat the bearings, but oil passing through to quickly won't have time to absorb any heat.. These are the reasons the clearances are "suggested" to be of a certain size...
Bottom line, the oil pump is the "Heart" of the engine as it pumps life giving oil throughout the system.. I will not run/use a new pump "out of the box" without careful inspection of the internal pump clearances. Surprisingly only about 1 out of 10 "Engine Builders" are even aware of what the internal numbers should be, or have the inspection tools to adequately inspect them...
How many here have seen a FORD FE "hex drive" twisted up like a pretzel??
Sorry for the long post, but I really feel the success or failure of an engine build relies so much on the choice of oil pump, oil pan, and correct pick up...AND the oil FILTER w/ a built in by pass feature...
Ray
 

RiverJeff

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Well I have an update, still not fixed.

Boat was out this weekend and I am still having the same issue with pressure loss above 4,000rpm.

I installed the Melling 10778C anti-cavitation pump and checked pick up to pan clearance all good. Checked/calibrated dip stick with pan off and checked baffles/windage tray in pan all good.

The anti-cavitation pump some said was not good at idle, for posterity I have ~30psi at idle 900rpm 20w-50 oil.

Moneypit was thinking the pressure loss could be coming from the non-bypass filter. Theory was if the filter was a restriction to flow at the higher rpm then maybe that would be a factor. To test this I plumed my remote oil lines together eliminating the filter from the system temporality. So with now no filter (basically as if the bypass was in place and open) I still have the same pressure drop off at +4000rpm.

Up to 4,000 RPM - stable 62psi could run all day
4,100 - drops to 45-50psi
4,400 - drops to 40-42
4,500 - drops to 38-40
+4,500 - drops below 35psi and I back off pressure jumps back

All verified with new mechanical gauges, 1 at filter port, 1 at front of block end of lifter gallery (bowtie block has a tap port there), and electric gauge at filter port.

I re-plummed the filter back in line and exact same results.

I reved up to 5000rpm for a couple seconds then shut it off and checked the dipstick for bubbles and I do have bubbles.

So new theories;

Im back to thinking this is a windage problem. Obviously I’m getting air in the oil but why? The Milodon jet boat pan has a full length windage tray with crank scrapers, baffle system around the pick up and I check all is working right.

Im running the correct amount of oil verified with the pan off. I have restrictors 0.060” in the lifter gallery (this problem existed with and without these).
  • Could aeration be caused by crankcase pressure? I have 2 breathers 3/4” and open but no PCV system (no manifold pressure at WOT anyway). Would a vacuum pump solve this?
  • Do these oil pan systems just not work? Ive spoken with Milodon multiple times and they swear they haven’t had this issue.

What else guys Im running out of parts to change… Thanks!
 

Boat 405

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It's the oil pan. You need a good kickout style pan. It's just windage, Box style pans like you have from Milodon are famous for this kind of stuff.

Look at a pan from Williams or Olsen. They will have a big kickout on the starter side of the pan.
 

Lavey 29

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I deal with Moroso every week . I would look at their pans and windage. Let me know if you need help. Moroso makes parts for me on the marine side as well.
 

DaveH

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i saw a similiar issue on a guys buggy.

all it was was low oil level.

the problem was, he would check the oil after it was sitting for a bit and it would all drain back in the pain and the level looked good. However, after running it at RPM for a bit and quicly shutting it off and checking the oil level....it was down several quarts, and starving the pump.

some would argue poor drain back, but once the oil was brought to the high mark on the stick AFTER a good run (making it look over filled after sitting) the pressure issue went away.

maybe the original builder marked the stick to low, i dont know. it was a custom engine.
 

Dansblown73Nordic

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Lots of oil pressure issues with those Milodon pans. If you do a search you will find plenty of other guys with the same problem. The pan always is the cause.
 

rivrrts429

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I had a Milodon that did the exact same thing as you did. I did all the same checks you did and everything checked fine.

My Dad told me to switch the pan.

Went to an Olsen and never had an issue again.
 

RiverJeff

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Well hey there, its been a while. How about a Corona Virus Update?

Taking advice from the forum and from B1 Racing, I bit the $900 Dan Olson bullet and had them fab up an 11qt wet sump pan for the Daytona. A couple weeks ago I swapped that pan with the Milodon and Dan Olson's pickup. Running 20w-50 Lucas racing oil.

This week with the work from home orders I was able to work from the "home office" and do some test runs. Wouldn't you know it the damn thing is holding oil pressure!
Held 5000rpm for up to 15min up river and the oil pressure sits at ~60psi. I am cautiously optimistic this solves the problem, my only hold out consideration is the temp (pretty cold now vs. summer).

So what do you think, was it the extra 1 qt this pan has? Is it Dan Olson's windage tray vs. Milodon's? Or is the pick up design better?

(anyone looking for a Milodon jet boat pan with less than 2hrs?)

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zx14

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Been watching this, glad you got it figured out.
 

obnoxious001

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I am coming into the game late here, but Milodon pans have a reputation for that exact problem, coupled with your longer stroke 572 engine that will greatly increase windage. I can't see the windage tray in the Milodon, they are usually a louvered type. I also don't like the perforated metal oil pickups, preferring the screen type that clearly allows more flow.
 

DaveH

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take a close up pic of the internals of each pan and post for comparison.
 

Teague_JR

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Windage tray and widened sump profile fixed it. Your big stroke motor, especially without a knife edged crank, is a windage monster.
 
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