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Chrysler 313 motor oil pressure issue.

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2 months 4 weeks ago #251547 by Blackduck59
Sounds like excess clearance, either mains, big ends or little ends.  Hit the throttle and the load go's on the piston and opens up the clearance on one side.
I see it with my Cummins but only a couple of PSI.
That is a very large drop.
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2 months 4 weeks ago - 2 months 4 weeks ago #251551 by jon_d
I keep coming back to my first reply on the first page.

"One as mentioned by others.  The inlet of the pump is partially blocked and the pump is cavitating at higher engine speeds.  (or an after market pump with a to high flow rate that doesn't match the gallery/inlet flow rates, again causing cavitation.)"


Pump is cavitating.  What oil is being used?
Is the pump original or after market high flow? 
What sump is fitted? Shallow dish? Deep dish?

And, has the oil pressure issue just started or always been there since the rebuild?
Last edit: 2 months 4 weeks ago by jon_d.

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2 months 4 weeks ago - 2 months 4 weeks ago #251553 by Blackduck59
Not sure with this, he only mentioned light on and off of the throttle, not a lot of revs. Indeed a strange one.
Last edit: 2 months 4 weeks ago by Blackduck59.

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2 months 3 weeks ago #251555 by JOHN.K.
Sounds to me to be something to do with the gauge.

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2 months 3 weeks ago #251556 by cliffo
Thanks for all your input but i was hoping for someone to have had this problem and found the cause. In summary A the issue comes at all revs B a blocked screen or hole in pickup would lower oil pressure permanently and the pressure would not vary C Used a master gauge in place of truck gauge with exactly same readings D only logical thought is that when powering there is different forces on pistons etc which somehow lets oil escape thus lowering pressure. First thoughts are main or big end bearings but if the clearance is big enough to leak 50 grade oil I would expect some unusual noise such as knocking etc but the motor runs smoothly and no unusual noises can be heard using a stethescope against the block. Dunno

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2 months 3 weeks ago #251557 by grumpy gumpy
In regards to point B, a partially blocked screen would not affect oil pressure all the time, mostly only under load when the demand for oil was greater ie; increasing revs
Gumpy
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2 months 3 weeks ago - 2 months 3 weeks ago #251558 by jon_d
B a blocked screen or hole in pickup would lower oil pressure permanently and the pressure would not vary

Incorrect.  I suggest you read up on cavitation and fluid dynamics

The pump will instantly attempt todraw more,  the mass of the oil in the suction tube  will be slow and will not flow instantaneously. Cavitation in the pump occurs. The oil technically boils in low pressure.  Gas is given off becuase the oil doesn't flow and the pressure drops.

As the oil/fluid velocity catches up in the suction line, the pump stops cavitating and the pressure returns.

I'll ask this question the 3rd time.   Has the oil pump been replaced with a high flow or high pressure pump?
And this the 2nd time, what oil is being used?

The other comments about blocked pick-ups, restricted flow access, shallow pans still stand.
I don't think it there can be any other cause.

Post-script:  Where is the oil pressure being sensed from?   Before the oil filter or after?   If before, then you might be observing the filter's by-pass valve opening. (unlikely, as the pressure should be picked off after the filter.)

 
Last edit: 2 months 3 weeks ago by jon_d.
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2 months 3 weeks ago #251559 by cliffo
oil pressure taken out of top of block between v where originaly fitted.Presume Oil pump is standard as motor never touched before I got it Gone to 20w 60 oil and made no difference. The oil pump is always running at camshaft speed regardless of whether the engine is pulling or throttle off so i cannot see any connection between oil pump and throttle on or off at set revs whether it be 1000rpm or 2000rpm. I acknowledge that the faster the motor is revving the faster the oil pump is turning and so putting out more capacity which the releif valve dumps when the pressure exceeds 50psi. Again I say that the oil pressure is varying by 20psi at the same revs of the motor within 100 or so just by touching the accelerator when overrunning either going downhill or slowing down to stop

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2 months 3 weeks ago #251560 by JOHN.K.
Is the oil overfull? ....if the crank hits the oil,it foams and pressure drops quickly.
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2 months 3 weeks ago #251562 by cliffo
oil right on full mark and I dont think power on or off would make any difference as crankshaft is spinning at same speed both ways

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