oil pressure dropping over 5000 rpm

Belgian1979vette

Belgian1979vette

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I already asked on another forum but no final solution yet. The thing is I'm running a HV pump with 75 psi spring and anti-cavitation slots. I have a oiling system including Canton 15-240t pan, thermostat, B&M Hi Tek oil cooler (stacked plate), accusump (with epc valve), remote oil filter.

The thermostat normally bypasses (up to a %) as long as the oil is not fully warmed up.

Getting around 75 psi when cold. No problem there.

Last weekend, with +30°C outside temps, engine got to 210°F. As soon as it was getting warm, I had around 55-60 psi oil pressure below 5000, around 25-30 hot. But going over 5000, made oil pressure go down...I saw it go untill 45-50 psi.

There is some debate about the accusump having a tendency of overfilling the pan, but I somehow have the impression that the oil cooler is causing the restriction.

Anyone ever run into this same problem with the B&M ?

PS : I know there is debate about the HV pump, but I run a pretty large system and spring oilers. There is no way on earth the pan gets sucked dry as all excess oil normally gets routed back to the intake side of the pump.
 
are you pumping the pan dry? how many quarts are you running in the motor?

It's hard to see how the drains are working, but did you deburr the drains when you did the motor? With high-volume/high-pressure pumps you can literally pull so much oil from the pan that you'll start sucking air because it can't drain back fast enough.

This might be as well:

Depending on the design of the oil cooler and oil filter base - you could simply be bypassing the cooler and filter under high pressure thus still getting too much oil up top.
 
SuperBuickGuy said:
are you pumping the pan dry? how many quarts are you running in the motor?

It's hard to see how the drains are working, but did you deburr the drains when you did the motor? With high-volume/high-pressure pumps you can literally pull so much oil from the pan that you'll start sucking air because it can't drain back fast enough.

This might be as well:

Depending on the design of the oil cooler and oil filter base - you could simply be bypassing the cooler and filter under high pressure thus still getting too much oil up top.
Click to expand...

I have a hard time seeing how it can pull the pan dry. If it starts pumping too much oil, it still has to get through all the passages. That will normally cause the pressure to rise and hit the set point of the spring in the pump, which is what i'm seeing at idle. If I check the volume of oil in the pan after it ran up to 75 psi cold, I'm still above the add mark. (to note is that the accusump draws some oilvolume as well which is variable based on pressure, but that aside).

The oil on top can only get there throught the pushrods, which allow the same amount of oil on top.

It will bleed off somewhat more since I have normally got a 70-75 psi spring in it. IMO it will not be enough to draw the pan dry.

The pan has 7 quarts actual oil content (without taking into account the filled filter, oil cooler and everything). If the total 7 quarts would end up on top, it would simply run out of my breather which is not the case.

It almost looks as if the pump cannot keep up.

BTW : to be sure I just changed the oil filter and cut the old one open. No metal scrapings in there.

The pump is of the type with the anti-cavitation slot in it.
The drains were deburred.
 
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Belgian1979vette said:
SuperBuickGuy said:
are you pumping the pan dry? how many quarts are you running in the motor?

It's hard to see how the drains are working, but did you deburr the drains when you did the motor? With high-volume/high-pressure pumps you can literally pull so much oil from the pan that you'll start sucking air because it can't drain back fast enough.

This might be as well:

Depending on the design of the oil cooler and oil filter base - you could simply be bypassing the cooler and filter under high pressure thus still getting too much oil up top.
Click to expand...

I have a hard time seeing how it can pull the pan dry. If it starts pumping too much oil, it still has to get through all the passages. That will normally cause the pressure to rise and hit the set point of the spring in the pump, which is what i'm seeing at idle. If I check the volume of oil in the pan after it ran up to 75 psi cold, I'm still above the add mark. (to note is that the accusump draws some oilvolume as well which is variable based on pressure, but that aside).

The oil on top can only get there throught the pushrods, which allow the same amount of oil on top.

It will bleed off somewhat more since I have normally got a 70-75 psi spring in it. IMO it will not be enough to draw the pan dry.

The pan has 7 quarts actual oil content (without taking into account the filled filter, oil cooler and everything). If the total 7 quarts would end up on top, it would simply run out of my breather which is not the case.

It almost looks as if the pump cannot keep up.

BTW : to be sure I just changed the oil filter and cut the old one open. No metal scrapings in there.

The pump is of the type with the anti-cavitation slot in it.
The drains were deburred.
Click to expand...

pressurized to the top, gravity to the pan - and it's not theoretical, the filling the top of the motor and starving the bottom; I've seen it happen. The issue is the high volume pump, unless you have a turbo or something that requires extra oil flow; they're just not worth it. (IMO 75 psi is a lot, and a waste of hp - 50 max, 25-30 psi warm would be about perfect).

it also might be that your pump is cavitating - the oil has to go somewhere, and if you push too much into the oil galleys; it could be sucking air or aerating the oil (cavitation) .... here's a wiki on the situation.
https://en.wikipedia.org/wiki/Cavitation
 
read up on Grumpy's reply in this old thread :

http://forums.hybridz.org/topic/3012-oil-pressurehow-low-is-too-low/

I have had my covers off immediatly after stopping the engine to set valve lash on 1 cyl. There was the normal amount of oil in there. This whole : sucking the pan dry is a bogus idea.

When hot it turns usually around 25-30 psi idle and 55-60 untill 5000. After 5000 i'm seeing it drop.

I'm going to assume pumped volume is high enough, so this leaves restrictions in the circuit and these can be :
- oil filter (non bypass filter AC Delco PF2)
- oil cooler
- the 90° bends I had to use
 
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dont know how it come up but my dad told me about jaguar 6cyl development, reckons they had main bearing starvation problem. Turns out the oil passages to bigend were to big and at revs centifigal force would force oil out of bigend faster than main gallery could supply it. so fix was to reduce drilling in crank,problem solved apparently. just something to ponder.:D
 
New testing I did with the filter I replace yesterday and disconnecting power to the accusump suggest both a combination of the oil filter and oil level in the crankcase to be part of the problem.

Going to look further into this and try another brand filter among a reduction in oil level. The latter is especially problematic since the amount of oil the accusump stores and dumps into the pan is dependant on oil pressure which changes with temperature of the oil.

With regards to the last statement on oil channel diameter. I know about the discussion relating to crossdrilled cranks (which mine is btw and unfortunatly I knew about this only after I bought it). What I find strange is that if centrifugal force prevents oil to flow out of the oil channels in the crank I would suspect the pressure to rise rather than drop. I'm no engineer so I could be wrong though.
Anyway I only saw the subject come up with engine running at or above 8000 rpm. I'm below that level.
 
In my previous engine configuration I was experiencing the same problem and after any kind of test, 3 different oil pan and 3 different oil pump...... the problem was in the high part of the engine!!!!!

My Worldcasting block was partially incompatible with my TrickFlow heads !
The oil drain hole in the heads was too little and partially blocked by the block shape..... basically, after few seconds at high rpm, all my oil was under the valve covers !!! :twitch:

Then, after some grinding in the heads and the block, the problem was solved.

Now, same block but Dart Pro1 227cc full CNC heads.... no problems!
 
Stroker-427 said:
In my previous engine configuration I was experiencing the same problem and after any kind of test, 3 different oil pan and 3 different oil pump...... the problem was in the high part of the engine!!!!!

My Worldcasting block was partially incompatible with my TrickFlow heads !
The oil drain hole in the heads was too little and partially blocked by the block shape..... basically, after few seconds at high rpm, all my oil was under the valve covers !!! :twitch:

Then, after some grinding in the heads and the block, the problem was solved.

Now, same block but Dart Pro1 227cc full CNC heads.... no problems!
Click to expand...

Correct, but I found this out when doing trial assembly. The block was already grinded before it was put together, so this is not the issue.

Meantime, I pinned it down to 2 possible causes : oil filter and pan overfill (possible promoted because of the accusump dumping partially its content in the pan during operation when pressure drops)
 
An update to this. A lot of tests later I ruled out some possible causes.
The filter was not one of them nor was a high oil level (so it seems).

I got better results running a 5W30 and currently due to what I'm seeing I'm inclined to believe it was oil pump cavitation. (BTW I checked oil levels while in running condition and hot at elevated oil pressure but oil level in the pan was correct)
 
This continued and for those who have the same issues : I still experienced a drop in pressure with the 5W30 and 6qrts, although less. I thought it was an oil drainage problem in the block and at first added about 700 ml. That made it worse, so it was pretty clear it was windage related. I drained some oil out of it with the oil level ending slightly below 6qrts and after that I had a solid pressure again at rpm.
 
This is very strange situation because these engines have the tendency to keep oil in the upper area of the block (lifter walley and valve covers).

Really looks windage related, but with tray and scraper....... mha!

There is allways something new to see.....
 
Well the story continues. Although I saw less of a drop with the 5W30 it wouldn't go up to the bypass relief valve setting which is strange since the volume produce by the pump goes up. It either has something to do with the bypass or cavitation.

I got a pump graph from Melling and what i'm seeing on my engine irl seems to be confirmed by the graph. There is a lot of debate on what could have caused this.

The thing is that people running below 5500 will probably never see this problem.

I'm still searching for a solution. It might end up with a dry sump, although on our cars that's a lot of hassle.

IMG_0233_zps605fa6b8.jpg
 
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the pressure section of a dry sump is a gerotor pump unlike the simple gear pump you have now. Cavitation, surge ..whatever it is, it's inherent to the simple 2 gear design

Titan makes a gerotor pump for SBC


There once was a setup that had a hybrid pump. A barnes in pan dry sump pump. They are very very ahrd to find but easy to use as it only requires the pan (not available anymore) or mods to your existing pan and 2 lines from the side of the pan.
 
Twin_Turbo said:
the pressure section of a dry sump is a gerotor pump unlike the simple gear pump you have now. Cavitation, surge ..whatever it is, it's inherent to the simple 2 gear design

Titan makes a gerotor pump for SBC


There once was a setup that had a hybrid pump. A barnes in pan dry sump pump. They are very very ahrd to find but easy to use as it only requires the pan (not available anymore) or mods to your existing pan and 2 lines from the side of the pan.
Click to expand...

yes, but the Titan pumps are wider in the back, necessitating a change in the pan apparently. Even then, cavitation originates from the inlet side and the drop in pressure, so it all depend on the inlet.

I know there has been talk about the barnes in sump dry sump, but quite frankly I've never even seen a picture of one. But even then it would still need an external tank.
 
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