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Discussion Starter #1 (Edited)
My '94 Caprice has about 12K miles on a bottom-end rebuild, in which the builder used a high-volume oil pump. Wear metals are high for iron and chromium, which leads me to think he screwed up with the rings (incorrectly gapped? broken?)

I figured maybe there was a slight chance that the issue was oil-pressure related. I have been running Mobil1 0W40--my BMW M5 and my wife's GL450 call for it specifically, and my '04 Mustang Cobra turns the best wear numbers on 0W40 compared to 5W30 or the factory-recommended 5W20. On a cold start when it's 50F, oil pressure is at ~60 PSI at idle. If I get up to 3000 RPM while accelerating on a cold motor (it has a 3K-stall converter, so even when babying it, it usually runs 2500-3000 RPM), oil pressure climbs to right at 80 PSI.

When warmed up, oil pressure at idle is around 50 PSI. If I put the car in second gear and accelerate from idle to 5500 RPM or so, the oil pressure climbs progressively with RPM. If I mash the throttle, the oil pressure first starts to climb, then drops to around 50-55 PSI as the revs climb in first gear. Then in second, oil pressure climbs up to about 80 PSI by redline.

Is the oil pressure drop normal? IE, is it the pressure relief spring in the oil pump just bleeding excess pressure? Or is the oil pump cavitating briefly?

I just switched to Mobil1 Advanced Fuel Economy 0W30 (I figured it gets better fuel economy by being easier to pump, and that ought to mean more power, too) and took a couple of videos doing pulls. Have a look and see if the oil pressure behavior looks appropriate.

Should I think about switching to 0W20?!


 

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First thing most will tell you is you cannot trust the factory gauge for an accurate PSI reading.

I'm no expert but from my experience your oil pressure does not look uncommon for a high volume oil pump.
 

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I would never rely on those glorified "idiot lights" in the first place. Who knows what the actual oil pressure is. Invest in some quality gauges if you're interested in accurate info.
 

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Is the oil pressure drop normal? IE, is it the pressure relief spring in the oil pump just bleeding excess pressure? Or is the oil pump cavitating briefly?


Should I think about switching to 0W20?!
yes on pressure release... possibly on cavitation if you were in a hard turn when it occurs

typically with HV pump builds the bearing clearances are "slightly" wider than stock and a thicker grade oil is used (20-50) which allows for a thicker oil wedge between bearings and metal...good thing on motors that will spin above 6k rpm

IMHO you should run the oil grade the motor is spec for (ex. use the 0-20 in the Cobra as it has tighter bearing clearances)

Your dash gauges are...well "for general reference" are OK and nothing they are doing is abnormal. Aftermarket gauges would be more specific on readings

FWIW my HV 383 has a cold idle of 50-55 and hot idle at 45-47 (Aerometer gauge). I use 20-50....and no there is no oil pump drive gear wear. Again, oil grade is directly correlated to bearing clearances. On old tired motors where bearings have worn opening them up people would go a wgt heavier on oil as more a band aid fix if oil pressure got to low. Doesn't fix the core problem but does extend the operation of the motor
 

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Yeah, verify OP with a decent mechanical gauge. Factory gauges are useless IMHO.
Also cold oil pressure is not very useful info, a clapped out engine could have spectacular cold oil pressure. What matters is normal temp OP readings.
 
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