Another oil pressure question......

[RECHRGD]

As some of you know, I recently had some oil pump issues that seem to have been resolved with the installation of a new Melling HV pump on my 440.  This last weekend I took a road trip of a couple of hundred miles at highway speeds.  About halfway through the trip I noticed that the pressure had dropped from 60 to 40 pounds.  It seemed to vary between those values for the remainder of the trip.  When on the road, rpm was between 2800 and 3200 with the lower pressure at the higher rpm.  Pressure at idle returns to around 60, so it seems to me that the engine is still fairly tight.  The oil level was at full. The short block has 50k, well maintained, miles and then top end has around 15k.  A six quart Hemi pan (with windage tray) and new 3/8" pickup was install at the time the top end was redone.  I have run Valvoline 20/50 VR1 oil the last several years with no problems.  Overheating is not an issue.  In fact, I changed the radiator a couple of years ago and it stays steady at only 180 degrees.  Now that it runs cooler than it used to, could the 20/50 weight oil be too heavy, preventing proper drain back into the pan at the higher RPM?  I'm thinking of changing to some 10/30 and going for a high RPM cruise.  Any other thoughts?

[TommyGun]

I have a similar issue at high rpm and I wonder if we are having the same problem.  I don't know what my oil pump is but it must be a high pressure of some sort because I have 80 psi pretty much all the time. When Im on the highway at 65 mph I have 80 psi, as I speed up I can watch the pressure drop as if the pump is sucking the pan dry.  Also I lose pressure stopping quick or turning quick like going around a round a bout which I think is due to no windage tray and the low oil level in the pan due to the pump.  When your at your higher rpm if you slow down does pressure increase? Maybe your pump needs a little more oil capacity?

[RECHRGD]

I have a similar issue at high rpm and I wonder if we are having the same problem.  I don't know what my oil pump is but it must be a high pressure of some sort because I have 80 psi pretty much all the time. When Im on the highway at 65 mph I have 80 psi, as I speed up I can watch the pressure drop as if the pump is sucking the pan dry.  Also I loose pressure stopping quick or turning quick like going around a round a bout which I think is due to no windage tray and the low oil level in the pan due to the pump.  When your at your higher rpm if you slow down does pressure increase? Maybe your pump needs a little more oil capacity?

Yes, if I slow down the pressure slowly rises...

[c00nhunterjoe]

 my bet is you are pumling the pan dry with the hv pump turning those consistant long term rpms and the 20w50 is unable to return to the pan fast enough. Imo, a 6 qt pan is not enough for rpm and hv oil pumps.

[RECHRGD]

my bet is you are pumling the pan dry with the hv pump turning those consistant long term rpms and the 20w50 is unable to return to the pan fast enough. Imo, a 6 qt pan is not enough for rpm and hv oil pumps.

Makes perfect sense...  But, it had a HP pump on it before with no problems. In fact, it had an HP pump before changing the stock pan out to the six quart one.  The only change in the mix is the fact that it now runs cooler than before......

[c00nhunterjoe]

High pressure and high volume are 2 different things. Which did you install?

[RECHRGD]

High pressure and high volume are 2 different things. Which did you install?

Sorry, my mistake.  The present and past pumps were both HV........

[Challenger340]

Without knowing the actual bearings clearances(rods & mains) used in your build ? or actual Oil Temperatures the engine is seeing ?, this is a tough problem to diagnose.
My point being..... Oil Temps can vary greatly from Radiator "Temp" seen on a gauge. Just because your Engine is running cooler water temp, does not mean your Oil Temp is not increasing dramatically at higher rpm(tight clearance) and thinning out causing Oil pressure to drop ? 
Just something else to check if drainback/oil pan capacity is not the problem, try thinner Oil.

[RECHRGD]

Without knowing the actual bearings clearances(rods & mains) used in your build ? or actual Oil Temperatures the engine is seeing ?, this is a tough problem to diagnose.
My point being..... Oil Temps can vary greatly from Radiator "Temp" seen on a gauge. Just because your Engine is running cooler water temp, does not mean your Oil Temp is not increasing dramatically at higher rpm(tight clearance) and thinning out causing Oil pressure to drop ? 
Just something else to check if drainback/oil pan capacity is not the problem, try thinner Oil.

Good points!  I'll just go ahead and change the oil out to 10/30 and see what happens.

[BSB67]

So you think that the pan is being sucked dry after the first hour of driving when the oil is good and hot and at its most flowable?  But not sucking it dry in the first hour?

[RECHRGD]

So you think that the pan is being sucked dry after the first hour of driving when the oil is good and hot and at its most flowable?  But not sucking it dry in the first hour?

Well, I was asking for other thoughts.......

[PlainfieldCharger]

 

[flyinlow]

What type of oil pressure gauge do you have?   A known good mechanical one ? 

[RECHRGD]

What type of oil pressure gauge do you have?   A known good mechanical one ? 

The gauge is the stock unit with a new sending unit.  I checked it against a mechanical gauge.  It took three new sending units before I got one that read right......

[flyinlow]

I guess what I am getting at is with an electric gauge (especially a stock 45 year old one)  voltage variance's could be causing the reading changes. The factory gauge dash board voltage regulator or a Chinese sender that is changing value with temperature build up. 

With readings from a known good mechanical I would be more certain of if there was a problem with the engine. 

I use the factory electric gauges with an idiot light as a back up. I have seen a couple times where the oil pressure and temp changed reading from normal ,then went back to normal. It got my attention but a check with a mechanical gauge showed the engine was fine.

[RECHRGD]

I used to have issues with the old gauges due to the original IVR.  I have since replaced it with an electronic unit and even had the whole cluster restored and calibrated a few years back.  Good thought though.  My issue certainly seems to be RPM driven.  I'm going to put a new filter and some 10/30 VR1 in it on Monday and hit the highway.......

[c00nhunterjoe]

If the oil doesnt fix it, reverify with a mechanical gauge anyway, an ir thermetor on the pan when the pressure drops may shed some light too

[RECHRGD]

I switched out to 10/30 today and things seem to be as they should be.  Last week I took a fairly long drive with the 20/50 in it to document what it was doing.  It would stay at 60+ lbs.  during hot idle.  At hwy speeds it would vary from 60 to 45.  Under hard acceleration from zero to 100mph it dropped to 40lbs..  TODAY while taking the same drive it would hot idle at 40/45 lbs..  While climbing to hwy speeds the pressure climbed to 60lbs. And stayed pretty steady.  The 0 to 100 blast netted 60+ lbs. from the 40+ at idle.  I will keep my eye on things, but, for now I'm happy.......

[ws23rt]

Thanks for the update.

  I always like to here "the rest of the story" on a topic that is sorting out a problem.

[flyinlow]