can high oil pressure affect how a lifter works?

JeffP1167

JeffP1167

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On my 97 3.8 Firebird I'm hearing what sounds like lifter tapping an wonder if the high oil pressure is the cause.

My other 97 3.8 builds around 50psi but this one can almost peg the gauge at 120psi (sender changed) made no difference.

So curious if this high pressure could affect the lifters and this is what's causing my mysterious random misses.
 
the pump puts out whatever it puts out at a given Rpm..... that said, your pressure can only get that high if you use extremely thick oil (unlikely) or if there's a restriction like a clogged oil passage (likely).
a restricted passage would increase pressure as the pump is working to force a given volume of oil thru the restriction, it also limits the volume of oil that gets to the lifter or rocker arm..... so you're seeing high pressure at the oil pressure sensor but low pressure at the lifter.
 
JeffP1167 said:
On my 97 3.8 Firebird I'm hearing what sounds like lifter tapping an wonder if the high oil pressure is the cause.

My other 97 3.8 builds around 50psi but this one can almost peg the gauge at 120psi (sender changed) made no difference.

So curious if this high pressure could affect the lifters and this is what's causing my mysterious random misses.
Click to expand...

Doing the math, the internal plunger in a hyd lifter has a diameter of ~5/8", and an area of .3 square inches. With an oil pressure of 120 psi, to the lifter, the upward push on the pushrod is ~36 lb. Since the valve spring force is roughly 90 lbs when the valve is closed, an upwards force of 135 lb is needed at the pushrod to even move the valve off its seat (with 1.5 ratio rockers). Therefore, with 120 psi oil pressure, the oil induced force is 99 lb short of what is needed to move the valve off the seat.

Short answer - No.

On the other hand, if the valve spring has failed, the lifter can pump up and hold the valve off its seat, but this would be obvious if you examined all the valve springs with a flashlight and inspection mirror.
 
I think first you need to find out why the pressure is so high... A buddy just blew two oil filters off his VW block .... He found there was dirt in the line restricting it .... I newer thought the pump could burst the filter but apparently it can .....
 
did you investigate a little more? just wondering.... 120psi is quiet a bit of pressure considering 40-60 is about "normal" .... probably even less with a stock pump and warm oil ....
I asked my buddy who blew the filter off the block, he says he has seen pressure up to 160psi with a mech gauge connected.... he blew 2 filters in a week while he was trying to figure out wtf is wrong with his oil system.....

what we've learned is: if you restrict the pump discharge the pressure will go up..... and something is going to give..... lol
 
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