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Old 07-12-2013, 05:08 PM   #1
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Default Normal Oil Pressure?

My idle oil pressure at 190 degrees is 18-20 psi then under normal throttle is 35-42 psi. Is that normal? I was always taught as long as you see the rise on throttle then you are fine because the sending unit may never be exact...

Thoughts?
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Old 07-12-2013, 06:14 PM   #2
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Its on the low side, but yes you need a real gauge on it instead of the sending unit.

It should start at 55-60 in the morning and come down some as the engine heats up. Under any throttle mine has always been over 50, but 45-60 is the spec, and 20-40 psi at idle depending on engine temp.

Rule of thumb is that you have to have 10psi for ever 1k RPM the engine is turning, or you have a problem coming.
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Old 07-12-2013, 07:02 PM   #3
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So I am good if the car is idle at 700-800 RPM and 18-20 PSI warmed up. When it's cold the pressure is much higher of course.
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Old 07-13-2013, 01:13 AM   #4
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Originally Posted by S S0DEN View Post
So I am good if the car is idle at 700-800 RPM and 18-20 PSI warmed up. When it's cold the pressure is much higher of course.
If you are concerned, the thinner the oil the lower the pressure maybe change from 20/50 to say 40/70 grade oil that will up the pressure a bit.

You can install a high volume oil pump with engine in the car, remove starter, drop the sump, remove the oil splash shield and oil pump.
Fit a mellings high volume oil pump (also the distributor to oil pump shaft needs a metal ring) That worked well with my old 350 some years ago with similar pressures and raised the oil pressure at idle and higher rpm.
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Old 07-13-2013, 01:19 AM   #5
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19 lbs at idle is plenty. 10 lbs/1k RPM as has been stated.
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Old 07-13-2013, 11:38 AM   #6
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Originally Posted by gerardvg View Post
If you are concerned, the thinner the oil the lower the pressure maybe change from 20/50 to say 40/70 grade oil that will up the pressure a bit.

You can install a high volume oil pump with engine in the car, remove starter, drop the sump, remove the oil splash shield and oil pump.
Fit a mellings high volume oil pump (also the distributor to oil pump shaft needs a metal ring) That worked well with my old 350 some years ago with similar pressures and raised the oil pressure at idle and higher rpm.
I am waiting on replacing the oil pump unless it was on it's way out. The engine is being replaced at the end of the year. I am just trying to understand what the normal operating range is for tpi 350.
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Old 07-13-2013, 11:39 AM   #7
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19 lbs at idle is plenty. 10 lbs/1k RPM as has been stated.
I got that, but I was receiving tips for increasing it
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Old 07-13-2013, 11:52 AM   #8
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Change the pump spring or pump altogether

Really, its a waste what you got is just fine.
Slippery slope though. Check the pump may as well check bearings too.
Timing chain probably loose too so...$$$$

Now your fix for a feel better oil pressure number was cured by a 10k stroker motor
just drive it
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Old 07-13-2013, 12:41 PM   #9
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Stroker is not a fix for me, when I traded for the car, it was already in the planning... $10,000? I built my last one for $3,500.
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Old 07-13-2013, 01:46 PM   #10
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I got that, but I was receiving tips for increasing it
I'm sorry. I thought you were asking what normal oil pressure was, and if yours was "normal". Yours is normal and fine. That was my point, and to back up what Vader86 concluded with.

The tips for increasing your pressure are potentially creating extra, unnecessary work for you. You don't need to change your oil pressure.
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Old 07-13-2013, 02:04 PM   #11
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Quote:
Originally Posted by gerardvg View Post
If you are concerned, the thinner the oil the lower the pressure maybe change from 20/50 to say 40/70 grade oil that will up the pressure a bit.

You can install a high volume oil pump with engine in the car, remove starter, drop the sump, remove the oil splash shield and oil pump.
Fit a mellings high volume oil pump (also the distributor to oil pump shaft needs a metal ring) That worked well with my old 350 some years ago with similar pressures and raised the oil pressure at idle and higher rpm.
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Old 07-13-2013, 02:06 PM   #12
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Originally Posted by Tom400CFI View Post
I'm sorry. I thought you were asking what normal oil pressure was, and if yours was "normal". Yours is normal and fine. That was my point, and to back up what Vader86 concluded with.

The tips for increasing your pressure are potentially creating extra, unnecessary work for you. You don't need to change your oil pressure.
Your oil pressures are fine. Drive on and enjoy your '88.
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Old 07-13-2013, 02:43 PM   #13
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Your pressure readings are totally normal. Move on
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Old 07-13-2013, 02:44 PM   #14
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Your oil pressures are fine. Drive on and enjoy your '88.
Thank you guys.
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Old 07-13-2013, 08:13 PM   #15
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So I am good if the car is idle at 700-800 RPM and 18-20 PSI warmed up. When it's cold the pressure is much higher of course.
count yourself amongst the lucky ones
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Old 07-14-2013, 01:14 AM   #16
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If you do a search on oil pressure you might find a very long, detailed write up done last yr on this subject...

Remember, in ANY hydraulic measurement, especially in oil pressures, that the gauge reading that you SEE is the end of the road for the oil...if you see 30 psi then there was 3 times that
(??? who knows???) at the main bearings where a large % is lost, whats left then goes to cam, lifters then on and up to valve train. AT the top of the engine the OP sender tell you whats left...
Another interesting point is that most filtration systems and filters have a bypass installed that is nothing more than a spring flap that is so soft that you can sneeze and make it open the dump port.

The filter bypass keeps the pressure from building to the point that the filter explodes, so you loose a lot of pressure right there at the very beginning of the system. I cannot say how much but a LOT of oil never makes it past the filter before it gets dumped back to the sump. Many folks suddenly see MORE OP after they install a new oil filter base or a stack-on cooler when they get a fresh bypass spring in there that is a little stiffer and lets more of the oil to go thru the system because its not getting dumped off so soon. Some folks suddenly see LESS pressure because they installed a softer bypass...nothing wrong with the engine but you'd think there was seeing the residual OP on the gauge.

Now, thicker oil is NOT necessarily better for a loose engine BECAUSE it MAY stay in the loose mains and hold more oil between the bearing and the crank surface, BUT it is also much harder to push thru the many more small orifices that it must go thru. Again, you will see whats left and with a heavy oil that may/may not be accurate since that's residual oil pressure after its done its job and it takes so much more to move the thicker oil.
My current engine with somewhere between 150 and 200,000 miles, and it idles
HOT (225* @ 600 rpm) @ 20-25psi. If I get stuck in 100+ ambients in traffic and my engine temps go to 230+ it MAY drop below 20 at 600 rpm. The instant the rpm goes up so does the pressure until freeway cruising speed at 17-1900 rpm gives me 40+ psi and more as rpm rises. IIRC 70-80 mph can get me 45-50 psi @ 200 degrees eng temp. That ain;t bad for an eng with this kind of milege.Usually it runs 20ish hot idle and 35+ anywhere above idle and this is a HI-MILES engine...it has been very well taken care of and I am run 20/50 syn summer and 5-30 syn winter and its always been dosed with
Pro-Long. An interesting note, the 5/30 will generate as much pressure or more in some situations than the heavier wt oil does...because it flows easier thru the system. Thick oil is harder to move.
I credit the "snake oil" ProLong,
(that's what science is called when folks do not understand it) with the high milege and the fact that it only uses maybe a 1/2 qt in 5000 miles.... Most of the small amount of oil that is used goes out thru the valve seals @ cold start or the wet spot on the drain plug....

Point is, if the engine is brand new and tight you will see LESS difference between hot/cold temp cycles. Once the eng is broken in and loosened up it WILL loose more oil thru the bearings thru slippage and the remainder of the oil that's still under pressure then makes it to the gauge, AFTER its gone all thru the engine.

Nothing will fix pressure loss thru worn bearings or loose valve guides/seals. Forcing more oil thru those worn areas does nothing more than provide more oil in vol that gets to the top end. It does not solve the problem or worn internal parts. That may provide a false sense of security for a while but as wear continues...the pressure will begin to fall again. If your oil TEMP rises sharply during brief hi-rpm runs, that's a sign that there is a LOT of slippage thru the bearings. Oil temp should be similar to water temp with some variation due to rpm.

As others have stated, 10 psi to 1000 rpm is what you NEED. If you have more than that then you have more than enough and if it is a great deal more, then you have plenty.

Bottom line, clean oil at lower pressure is better for an engine than high pressure oil that's lost its viscosity and carries a ton of dirt. Pressure isn't everything. Many engines are designed to run on low pressure/hi vol. I had a Bike hi-performance engine that was designed for 4 psi OP with a redline of 10500 rpm...That sounds plain scary, but it worked.

Last edited by leesvet; 07-14-2013 at 01:26 AM.
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Old 07-14-2013, 04:12 AM   #17
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Another interesting point is that most filtration systems and filters have a bypass installed that is nothing more than a spring flap that is so soft that you can sneeze and make it open the dump port.

The filter bypass keeps the pressure from building to the point that the filter explodes, so you loose a lot of pressure right there at the very beginning of the system. I cannot say how much but a LOT of oil never makes it past the filter before it gets dumped back to the sump.

Point is, if the engine is brand new and tight you will see LESS difference between hot/cold temp cycles. Once the eng is broken in and loosened up it WILL loose more oil thru the bearings thru slippage and the remainder of the oil that's still under pressure then makes it to the gauge, AFTER its gone all thru the engine.
This is an excellent write up; however may I elaborated further on a couple of points.

when the oil discharge from the oil pump enters the block, it immediately splits into two branches. The first branch leads directly to the rear main crankshaft / thrust bearing which receives unfiltered oil 100% of the time.

The second branch goes to the oil filter, and unless the oil pressure bypass has been eliminated (plugged) the remaining oil, may or may not be routed through the filter. Simply stated (except for the rear main which never receives filtered oil) the rest of the engine receives some filtered oil some of the time depending, as noted, on the condition of the bypass spring and how clogged, or clean, the oil filter is.

This filtered oil then goes up, this is where the oil pressure is measured, just before it enters into the rear of the camshaft oil gallery.

once it enters the camshaft oil gallery, the camshaft journals are lubricated. A portion of it is bled off to lubricate (pump up) the hydraulic lifters and thence to the valve train.

simultaneously SOME of the oil goes to the number 1, 2, 3, and 4 main bearings; what doesn't squirt out of the main bearings makes it way to the rod bearings.

a final note, as to the oil filter bypass, the oil that goes through the filter bypass does not dump back into the sump, it merely bypasses the filter on its way to the camshaft gallery. The only oil that does dump into the sump is from the oil pump itself when the pump oil pressure exceeds the spring pressure of the pump relief valve.
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Old 07-14-2013, 06:52 PM   #18
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Originally Posted by mtwoolford View Post
This is an excellent write up; however may I elaborated further on a couple of points.

when the oil discharge from the oil pump enters the block, it immediately splits into two branches. The first branch leads directly to the rear main crankshaft / thrust bearing which receives unfiltered oil 100% of the time.

The second branch goes to the oil filter, and unless the oil pressure bypass has been eliminated (plugged) the remaining oil, may or may not be routed through the filter. Simply stated (except for the rear main which never receives filtered oil) the rest of the engine receives some filtered oil some of the time depending, as noted, on the condition of the bypass spring and how clogged, or clean, the oil filter is.

This filtered oil then goes up, this is where the oil pressure is measured, just before it enters into the rear of the camshaft oil gallery.

once it enters the camshaft oil gallery, the camshaft journals are lubricated. A portion of it is bled off to lubricate (pump up) the hydraulic lifters and thence to the valve train.

simultaneously SOME of the oil goes to the number 1, 2, 3, and 4 main bearings; what doesn't squirt out of the main bearings makes it way to the rod bearings.

a final note, as to the oil filter bypass, the oil that goes through the filter bypass does not dump back into the sump,Correct, I mis-spoke and was thinking of the pump relief valve. it merely bypasses the filter on its way to the camshaft gallery. The only oil that does dump into the sump is from the oil pump itself when the pump oil pressure exceeds the spring pressure of the pump relief valve.
Which brings me to another question....I wonder how much of the oil that's critical at cold start, is lost to bypass and/or reliefs when the wt of the oil is too high?

Its well established that the majority of all engine wear takes place during cold starts when the oil is not circulating and it not warmed up. Something like 82%....that's why many of these "snake oil" products actually DO work because they fill in that gap when oil is not lubricating because it is not flowing yet...these chemicals provide some surface penetration of the metals with smaller molecules that can fit in places the larger oil molecule cannot, so they remain in place and do the job of lubricating when there is no oil present.

I am a believer after seeing the inside of an engine that had always used ProLong. After 150,000 miles the mains were tight, the pistons were barely scuffed, rings tight, everything else in good shape. The machine shop "gues-timated" the milage to be closer to 30,000.....not 150,000. That's what sold me on Prolong. The cold start wear is well known and the reason why the REAL big money engines all have oil warmers and pre-lube systems that send oil thru the engine from an accumulator to build oil pressure BEFORE the starter ever turns the crankshaft. If I ever get to build a nice engine from the ground up, it WILL have a pre-lube system...They're not that expensive either, just kinda difficult to find a place to mount an accumulator the size of a paper towel roll and a few more hoses.
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Old 07-14-2013, 07:10 PM   #19
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that's why many of these "snake oil" products actually DO work because they fill in that gap when oil is not lubricating because it is not flowing yet...these chemicals provide some surface penetration of the metals with smaller molecules that can fit in places the larger oil molecule cannot, so they remain in place and do the job of lubricating when there is no oil present.
yeah. but they DON'T actually do that...which is why they are snake oil.


Quote:
Originally Posted by leesvet View Post
I am a believer after seeing the inside of an engine that had always used ProLong. After 150,000 miles the mains were tight, the pistons were barely scuffed, rings tight, everything else in good shape. The machine shop "gues-timated" the milage to be closer to 30,000.....not 150,000. That's what sold me on Prolong.
O.K. but the problem with THAT, is you can get the same exact results w/any decent, modern oil....especially on a highway driven, 150k motor. 150,000 miles is nothing on a well maintained motor, anymore. Pre-lubers do work, but now days, most cars will fall apart around a well maintained stock motor.
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Old 07-14-2013, 07:50 PM   #20
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I am a believer after seeing the inside of an engine that had always used ProLong. After 150,000 miles the mains were tight, the pistons were barely scuffed, rings tight, everything else in good shape. The machine shop "gues-timated" the milage to be closer to 30,000.....not 150,000. That's what sold me on Prolong.
for what it's worth, I use ProLong myself.
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