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Well I've noticed over the last year a drop in idling oil pressure from looking at the guage. I'm driving about 40k a year so this might be more apparent to me than others. I'm part of the stampede, and hopefully will get a spring from CDan for next week. I'll let everyone know if I see a difference.
Does one need a aftermarket oil pressure guage to test the 3000+ rpm oil drop?
Is the dash guage good enough?
Does the vehicle need to be in gear or can it be parked and tested?
Do you think one should replace it at a certin milage (200k,300k,400K) or just keep an eye on it?
Is the dash guage good enough?
Does the vehicle need to be in gear or can it be parked and tested?
Do you think one should replace it at a certin milage (200k,300k,400K) or just keep an eye on it?
What nobody's answered to my satisfaction is, how does increasing RPM's cause the LOWERED pressure? If the spring is weak, it would succumb to a lower pressure than the estimated design of 75psi and open early (say at 55 for example). Then max engine pressure would be artificially limited to 55. But if oil pressure climbs to this limit, then the engine is revved higher and system pressure drops, would it not be an oil pump issue? The spring should still be allowing the system to remain at 55 at higher rpms, no?
'Splain this to me.
DougM
'Splain this to me.
DougM
Cruiserdrew
On the way there
I can't explain it, but my 190k FJ40 does the same. On a mechanical guage the oil pressure peaks at 45psi at 2000 rpm and drops to 40 psi at 3000 rpm. I replaced the oil pump and it still does exactly the same thing. I assume it means the mains are worn but it doesn't knock and runs just fine.
[quote author=e9999 link=board=2;threadid=12750;start=msg118372#msg118372 date=1078902302]
cavitation?
[/quote]
a possibility, but I do not think MR T would design the oil pick up so restrictive to allow that to happen unless a way out of spec oil was used, in Aus very thick oils are specified in the same motor, maybe if the screen and pickup tube were restricted with sludge
but if it was cavitation why did replacing the relief spring would fit it?
LandToy, from reading Robbie's post I get the impression that it is shown on the dash gage as well, I am sure he will clarify
for what it is worth did some “spirited” driving today and all the way to 4k oil pressure stays at or just above the 2/3 mark idle is near the 1/3 mark, this is with 15-40 Chevron Delo (dino) Mobil Delvac 1 going in tomorrow
cavitation?
[/quote]
a possibility, but I do not think MR T would design the oil pick up so restrictive to allow that to happen unless a way out of spec oil was used, in Aus very thick oils are specified in the same motor, maybe if the screen and pickup tube were restricted with sludge
but if it was cavitation why did replacing the relief spring would fit it?
LandToy, from reading Robbie's post I get the impression that it is shown on the dash gage as well, I am sure he will clarify
for what it is worth did some “spirited” driving today and all the way to 4k oil pressure stays at or just above the 2/3 mark idle is near the 1/3 mark, this is with 15-40 Chevron Delo (dino) Mobil Delvac 1 going in tomorrow
R
robbie
Guest
- Thread starter
- #28
Yes you can test this with the dash guage. From some past experences I never really trusted the dash guage. I also did not spend the money when I rebuilt the engine to have the right information (big mistake). THis should be done when the engine has fully warmed up and then it can be done park. Just rev the engine slowly up to redline and hold it and watch the pressure guage. Usually after 3500 or so rpm the oil pressure will fall off. simple test.
THe design of the pump allows the relieved oil to go back to the pump(self circulate). The pick up tube is huge and the screen area is huge. I beleive the only area air could be pick up is at the oil pan to timing cover o ring or the oil pump drive shaft that goes through the timing cover.(which I do not think is the problem).
Do not really know why the pressure falls off the way it does, when the engine is cold (cold oil) pressure build higher (psi), and falls off at about the same point (rpm's). The pressure relief may not handle the flow it is pushing at the rpms and the pressure it has at those rpm's. As pressure build flow is increased also. It may be more of a flow related problem and the relief can not handle the flow. All I really do know for sure the spring swap cured my problem. It may take talking to an technical engeneer to find out this answer.
THe design of the pump allows the relieved oil to go back to the pump(self circulate). The pick up tube is huge and the screen area is huge. I beleive the only area air could be pick up is at the oil pan to timing cover o ring or the oil pump drive shaft that goes through the timing cover.(which I do not think is the problem).
Do not really know why the pressure falls off the way it does, when the engine is cold (cold oil) pressure build higher (psi), and falls off at about the same point (rpm's). The pressure relief may not handle the flow it is pushing at the rpms and the pressure it has at those rpm's. As pressure build flow is increased also. It may be more of a flow related problem and the relief can not handle the flow. All I really do know for sure the spring swap cured my problem. It may take talking to an technical engeneer to find out this answer.
Not familiar with the term cavitation, so maybe this is along the same line of thing, but increased flow rate to the point of going from laminar to turbulent flow would result in a decrease in pressure,.. no??
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- Dec 11, 2003
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A relief valve opens when the pressure is too high, and whenever it opens, pressure falls because the flow is increased.
The problem is when the relief valve opens before it's supposed to do it, like in a weak spring, thus reducing the pressure before it is supposed to.
By changing the spring, you are restoring the design parameters as far as the pressure build up it is supposed to support before opening, however when it does open, pressure will fall.
Disclaimer: this is how a presssure relief valve works in general terms, I have not actually seen the relief valve for this particular application, but i bet this is how it works.
The problem is when the relief valve opens before it's supposed to do it, like in a weak spring, thus reducing the pressure before it is supposed to.
By changing the spring, you are restoring the design parameters as far as the pressure build up it is supposed to support before opening, however when it does open, pressure will fall.
Disclaimer: this is how a presssure relief valve works in general terms, I have not actually seen the relief valve for this particular application, but i bet this is how it works.
- Joined
- Mar 28, 2003
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- 1,189
Cavitation from my experience is caused by sucking air into a pump. For example on heavy equipment a rather common thing was for the machine to go low on hydraulic oil. To happen on the cruiser it would have to be really low on oil or maybe on a heck of a slant so the oil pump could not pick up. Anyway, it is very bad for a pump.
Just another thought on the spring deal - temperature also affects the tension of a spring.
Bill
Just another thought on the spring deal - temperature also affects the tension of a spring.
Bill
[quote author=Photoman link=board=2;threadid=12750;start=msg118849#msg118849 date=1078961058]
temperature also affects the tension of a spring.
[/quote]
Just ask a GM owner with hard hot starting issues
.
I was thinking that when the relief finally lets go the oil's temp influences the springs properties which then allows for more oil to flow and a drop in pressure
temperature also affects the tension of a spring.
[/quote]
Just ask a GM owner with hard hot starting issues
. I was thinking that when the relief finally lets go the oil's temp influences the springs properties which then allows for more oil to flow and a drop in pressure
hmmm...
not really.
If a pressure relief valve opens, it basically keeps the pressure constant at the point where it opened, unless it has some active control and a computer with it...
E
edit: oops, several posts already since the one I answered (Mty...'s). Sorry about confusion.
not really.
If a pressure relief valve opens, it basically keeps the pressure constant at the point where it opened, unless it has some active control and a computer with it...
E
edit: oops, several posts already since the one I answered (Mty...'s). Sorry about confusion.
[quote author=Photoman link=board=2;threadid=12750;start=msg118849#msg118849 date=1078961058]
Cavitation from my experience is caused by sucking air into a pump. For example on heavy equipment a rather common thing was for the machine to go low on hydraulic oil. To happen on the cruiser it would have to be really low on oil or maybe on a heck of a slant so the oil pump could not pick up. Anyway, it is very bad for a pump.
Just another thought on the spring deal - temperature also affects the tension of a spring.
Bill
[/quote]
cavitation can also occur if the liquid is not supplied to the pump as fast enough, this causes low pressure, if the pressure gets below the vapor pressure of the liquid at that temperature a gas pocket can form in the middle of the liquid as soon as the pressure comes back the pocket collapses making a lot of noise and possibly damaging the pump
the hydraulic systems I work with have a pressurized resivior, usually around 30psi, helps keep the pump from cavitating
there are other forms of cavitation more info here, don't think cavitation is the culprit in this case
http://www.mcnallyinstitute.com/01-html/1-3.html
Cavitation from my experience is caused by sucking air into a pump. For example on heavy equipment a rather common thing was for the machine to go low on hydraulic oil. To happen on the cruiser it would have to be really low on oil or maybe on a heck of a slant so the oil pump could not pick up. Anyway, it is very bad for a pump.
Just another thought on the spring deal - temperature also affects the tension of a spring.
Bill
[/quote]
cavitation can also occur if the liquid is not supplied to the pump as fast enough, this causes low pressure, if the pressure gets below the vapor pressure of the liquid at that temperature a gas pocket can form in the middle of the liquid as soon as the pressure comes back the pocket collapses making a lot of noise and possibly damaging the pump
the hydraulic systems I work with have a pressurized resivior, usually around 30psi, helps keep the pump from cavitating
there are other forms of cavitation more info here, don't think cavitation is the culprit in this case
http://www.mcnallyinstitute.com/01-html/1-3.html
Found the parts CDan mentions in his post above in my parts bin. Curious, searched, found this important post.
An overlooked (under appreciated?) fix to a very common and potentially serious issue.
Reviving this thread for our common good.
An overlooked (under appreciated?) fix to a very common and potentially serious issue.
Reviving this thread for our common good.