Oil pressure drops when RPM's increase - Team Camaro Tech
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post #1 of 65 (permalink) Old May 18th, 07, 10:22 AM Thread Starter
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Brad
 
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Oil pressure drops when RPM's increase

On my Camaro, I thought I had a big problem when the oil pressure all of the sudden dropped to 10-20 psi at cruise speeds, and below 15 psi when hot and cruising.... Changed to mech gauge, and replaced filter (FRAM) and oil pressure came back to reasonable ranges 25-30 psi hot idle and cruising. Drove it around a little more and all seemed ok. Well drove it around a little today and noticed the oil pressure dropping when at WOT from about 3000 to 6000 and let off when I saw the oil pressure at around 15..... Let car come back to idle and stayed around 15-20. Would rev and it would come up to around 25 but not much higher..... If I recall I have the HV55 pump and stock milodon pan, where should I start?

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post #2 of 65 (permalink) Old May 18th, 07, 11:47 AM
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Re: Oil pressure drops when RPM's increase

Wow...I would have guessed you had a high volume oil pump.
That's a classic symptom.

Is the Milodon oil pan a 5 qt ?
And is it shaped similar to stock ? (no kick outs etc.)
Is it a baffled pan ?
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post #3 of 65 (permalink) Old May 18th, 07, 01:31 PM
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Re: Oil pressure drops when RPM's increase

Yep, HV pump and stock pan..
You need to increase your pan volume.

Try over-filling by 1 quart and see if it makes a difference. If so, that's your problem..

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post #4 of 65 (permalink) Old May 18th, 07, 02:09 PM Thread Starter
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Re: Oil pressure drops when RPM's increase

The pan is the stock replacement from Milodon, no kickouts, etc. It is the exact same shape as stock.

Overfilling it by a quart, ok will try that out this weekend hopefully......

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post #5 of 65 (permalink) Old May 18th, 07, 04:04 PM
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Re: Oil pressure drops when RPM's increase

Overfilling the pan will just increase the windage and the oil will be frothy. This will definitely decrease your oil pressure.
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post #6 of 65 (permalink) Old May 18th, 07, 05:56 PM Thread Starter
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Re: Oil pressure drops when RPM's increase

update - I drove it around for about 15 miles and once it was about 10 miles oil pressure was around 15 psi. would drop to 10ish while on the throttle, but let off gas and was back to 15 psi again... would not increase much more than that... could the oil be a little thin from the heat? mobil 1 10w-30 synthetic...... ideas?

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post #7 of 65 (permalink) Old May 18th, 07, 06:34 PM
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Re: Oil pressure drops when RPM's increase

Brad: I don't know about other performance enthusiasts but I always considered 10w30 oils, Synthetic or Not, as Pony Piss. In my opinion, 10w30 will not handle the surface to surface pressures of Hi-Perf Engines. I prefer to use 15w40 and will use 20w50 if I can not find 15w40. Stay away from 10W40 as there are too many polymers in it. I highly Recommend Rotella Diesel Oil 15w40 as it is ZINC Based and will save your Flat Tapped Cam. Valvoline also makes a Race Blend Oil, advertised as "Off Road Use" which is also ZINC based. I also recommend ZINC Based Oils for Blocks that were originally designed for Flat Tappet then Retro Fitted to Roller Cams because of the poor lifter bore alignments found in Flat Tapped Engines.

It is not unusual particularly with 10w30 Oil for the Oil Pressure to drop considerably after the engine has warmed up and driven for awhile; however, the Oil Pressure should increase some what proportionately as the revs increase NOT Decrease, even with 10w30.

It is possible that you have larger bearing clearances then what is considered standard and as the engine heats up and is revved, the 10w30 simply can not fill the gap; hence the expression, "Pony Piss". Other then this, it is what Mark and Steve suggests that the Hi-Volume Pump has simply pumped the oil pan dry and you need more reserve by adding another quart or possibly the oil pump pressure relief valve may be stuck. Here's another thing, it is possible that the clearance between the Oil Pump Pickup and bottom of the oil pan is too small.

If you are not experiencing engine knocks, indicating a bad bearing, I would try using higher viscosity oil such as 15w40 and see what happens.

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post #8 of 65 (permalink) Old May 18th, 07, 06:37 PM
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Re: Oil pressure drops when RPM's increase

Brad..your clearances may require a 20-50 weight.I would try that first.The 4 qt oil pan will not be depleted at idle speed,increasing the capacity will result in aerated oil and further drops in pressure.If the 20-50 does not help..the oil pump pressure relief valve may be stuck in its bore.

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post #9 of 65 (permalink) Old May 18th, 07, 08:31 PM
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Re: Oil pressure drops when RPM's increase

My friend had a problem at WOT with his oil pump pumping faster than the oil could drain back which caused a drop in psi at WOT.

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post #10 of 65 (permalink) Old May 18th, 07, 09:08 PM
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Re: Oil pressure drops when RPM's increase

Quote:
Originally Posted by ace's68 View Post
My friend had a problem at WOT with his oil pump pumping faster than the oil could drain back which caused a drop in psi at WOT.
What does it do at half throttle?
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post #11 of 65 (permalink) Old May 18th, 07, 09:18 PM
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Re: Oil pressure drops when RPM's increase

Quote:
Originally Posted by onovakind67 View Post
Overfilling the pan will just increase the windage and the oil will be frothy. This will definitely decrease your oil pressure.
Overfilling by just one quart will not actually overfill the pan if the engine has poor oil return. This is an easy way to quickly find out if pan volume is less than enough.

As for oil weights, I don't think a 30 weight is a cause for concern. Most times a 50 weight will appear to provide better oil pressure simply because of the gauge's location between the oil pump and main gallery (BBC), or on the same oil feed gallery from pump to main (SBC). The gauge sees the pressure created by the pump trying to force a thicker oil through the engine, yet less pressure arrives at the far end.
A lighter oil shows as less pressure on the gauge because it is of less restriction and flows easier to the far end with less effort.
But at the same time it's true for the lighter oil to bleed off faster requiring more oil to be moved through the engine, or a slight drop in pressure.
So I am not for or against 30 vs 50 weight oil, just something to keep in mind that the factory oil pressure port's location is not optimum.
A better place for your gauge's sender is the front of the main gallery. This will provide a more relevant reading of mains pressure in a worst-case-scenario. In other words, I don't care how high my oil pressure is, I care about how low it is.

Maybe you're overheating your oil. You say your pressure drops after WOT. Got a pan gauge or IR gun?

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post #12 of 65 (permalink) Old May 18th, 07, 10:28 PM Thread Starter
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Re: Oil pressure drops when RPM's increase

THanks for the input guys! I will take a look at putting something better than 10W30 in there then. I am running a Hyd Roller Retro fit cam, if that helps with running a ZINC based oil or not.....

At part throttle, it stays constant @ 15 psi, when I am building boost and at WOT it seems to drop.... When the motor is cold it increases with RPM's until about 65 psi then holds steady.... But once its warmed up can't get it to go above 25 psi. I have 2 oil pressure tests, one is a 10 psi warning light connected to the line right where the oil filter is, and the other running to the gauge is on the drivers side front portion of the motor...

I don't have a IR temp gauge, that might be one of my next tool purchases... But I do know the pan is pretty hot to the touch after driving it today...

Forgive my ignorance, but can I access the oil pump pressure relief valve without pulling the pan? I have been told it is a big pain to try to pull the pan without pulling the motor...

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post #13 of 65 (permalink) Old May 19th, 07, 12:47 AM
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Re: Oil pressure drops when RPM's increase

Quote:
Originally Posted by BlackoutSteve View Post
Overfilling by just one quart will not actually overfill the pan if the engine has poor oil return. This is an easy way to quickly find out if pan volume is less than enough.
When is overfilling not overfilling? Could less than enough actually be more than plenty?

It's normal for your oilpan to be warm to the touch, normal oil temperatures are somewhat higher than the engine coolant temperature. You certainly won't be able to hold your hand on it.
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post #14 of 65 (permalink) Old May 19th, 07, 12:56 AM
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Re: Oil pressure drops when RPM's increase

Maybe, but if a heap of oil is up the top of the engine and taking it's sweet time to return to the pan, the pan is not actually over-filled during that time right?

Anyway, I've seen this test work several times to indicate pans that are too small or otherwise. It does work.

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post #15 of 65 (permalink) Old May 19th, 07, 05:56 AM
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Re: Oil pressure drops when RPM's increase

the fact that you`re trying to run a boosted sbc with 15 lbs of oil pressure scares me!!!but its not my motor...lmao...(sorry)anyway, did you put a fram filter back on the motor???if so, pull it back off, and get a good filter...fram is notorius for doing this exact same thing in our 70 nova ...(blown 383) but before we notice a pressure drop, the filter usually splits...happened twice before we vowed to badmouth fram filters every chance we got...lol...synthetic oil takes the heat better than conventional oils, but i`d want to go with a zinc based oil like the earlier posts said...(keep in mind that rotella is phasing out zinc also!!!)the bypass valve is also a great place to look, but i`d start with the filter first...fact is if you put a blower on an older motor, you can make alot of carbon in the oil, due to ring seapage...you cant see the blowby because it wont show at the breather until under boost...not that this is your problem, but just something to think about... SCRAP THE FRAM...

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