Oil pressure down to zero when idling.

[OzCharger69]

I'm seeking some help to troubleshoot my oil pressure problem. It's a reasonably fresh 383, Comp Cam (not sure which), stock oil pan, with maybe 2000 miles on it. I'm running a K&N filter and VR-1 10-40W oil. I have a Dakota Digital dash so any quick changes in oil pressure immediately shows on the dash.

Oil pressure is fine while driving around, it stays at 30-70 PSI depending on rpm. When engine is up to temp, the pressure will occasionally drop to zero when idling at the lights and picks up as soon as the car gets moving. This sudden drop to zero doesn't always happen at idle, but it definitely happens if I hard brake.

I'm start the troubleshoot with the following (in that order) -

1) Change the oil and put a Wix filter
2) Check the oil pressure relief valve
3) Check distributor shaft
4) Check oil pickup tube
5) Valve covers off to check for a dropped lifter

Any ideas on what else I should be checking?

 

[Don Frelier]

I would set up a mechanical gauge you can read and see if it's real.
A sudden drop seems unlikely unless your pickup is coming uncovered which should not happen at idle.

 

[Dave6T4]

I would guess that your oil pump pickup is not at the bottom of the pan.

 

[66 Sat]

While not related to your problem, I'd try a different (heavier) oil too. Most of the guys here in Queensland run Penrite HPR 30 (20w-60) or HPR 40 (25w-70).
I've run both in my poly, with no issues. It has the extra zinc protection and is suited to the older cars/hot climate.

 

[PlymCrazy]

This sudden drop to zero doesn't always happen at idle, but it definitely happens if I hard brake.

I'd suspect the pickup tube not being fully submersed when that occurs. Oil shifting to front of pan, leaving the pickup during a hard stop...

Deep oil pan? Shallow pickup? Any noticeable engine noise when it drops?

 

[Don Frelier]

Throw another quart of oil in it and see if anything changes.

 

[diesel_lv]

While not related to your problem, I'd try a different (heavier) oil too. Most of the guys here in Queensland run Penrite HPR 30 (20w-60) or HPR 40 (25w-70).
I've run both in my poly, with no issues. It has the extra zinc protection and is suited to the older cars/hot climate.

OP states pretty fresh 383 w about 2k miles on it. Depending on bearing clearances, 10w30, possibly 20w50. I'm in AZ w summer temps over 120°F. 383 stroked to 496. Run 10w30 without issue and no drop in pressure. High oil viscosity is for larger bearing clearances or band-aid for worn engine.

 

[BSB67]

Is this a new development, or has it always been this way?

 

[66 Sat]

OP states pretty fresh 383 w about 2k miles on it. Depending on bearing clearances, 10w30, possibly 20w50. I'm in AZ w summer temps over 120°F. 383 stroked to 496. Run 10w30 without issue and no drop in pressure. High oil viscosity is for larger bearing clearances or band-aid for worn engine.

I'm hearing you (and read what he wrote too).
I was surprised too when I received this advice from 3 different engine builders here, all very experienced with great reputations. I should have asked them why...
I was told to run these oils on both my fresh re-builds - the original 318 poly and then the poly stroker rebuild. Both were high performance (relative to a poly) builds, fresh machine work etc. Maybe they run looser clearances here as a matter of course? I'll ask next time I'm talking to them as I'd like to know myself.

 

[davek]

1st try mechanical gauge

 

[OzCharger69]

While not related to your problem, I'd try a different (heavier) oil too. Most of the guys here in Queensland run Penrite HPR 30 (20w-60) or HPR 40 (25w-70).
I've run both in my poly, with no issues. It has the extra zinc protection and is suited to the older cars/hot climate.

I haven't gone down that road because it's pushing really good pressures while running around town.

Is this a new development, or has it always been this way?

It's hard to say. When I had the stock gauges the needles move so slowly that I never noticed the change. With the digital gauges, I get alerted everytime it happens.



I will check it with a mechanical gauge though to confirm.. Thanks for the replies, I'll update everyone with the outcome of my investigations!

 

[diesel_lv]

One of the issues w digital gauges, you see every fluctuation n think something is wrong. Digital tach will read all over the place above n below desired rpm. But on an analog gauge, even a digital dial gauge, the rpm will show steady. Things such as AFR, RPM fluctuate a lot when looked at digitally, it'll drive you crazy. Stick w a dial gauge.

 

[drivintim]

This may sound crazy, but after you check with a mechanical guage, check your grounds. I had a bad ground on a fresh build, everytime i would brake the guages would change. The brake lights were back feeding through the dash effecting the guages.

 

[furyus]

If the gauge tells you to look further, you'll be dropping the pan. So I would check the bearings. I had the problem with zero oil pressure on hard braking. I fixed it with a Milodon oil pan. So, consider a baffled oil pan.

 

[66 Sat]

Bee1971 and the Red X and run.
Which part do you disagree with?

 

[Geoff 2]

[1] Add a litre of oil. If this fixes the problem then you know the p/up is too high off the floor of the oil pan....which will require oil pan removal to fix.
[2] To Aussie readers. Penrite, the go to oil. If you live in a hot part of Oz, I would use 10-10ths full synthetic, 10w/60. Colder areas 5W/50. It costs more but you are not replacing oil everyday!

 

[OzCharger69]

I spoke to the previous owner and apparently it has a Hemi oil pan and a Hemi pickup as pictured. Could this be the issue?

 

[AR67GTX]

It may be a Hemi pan but not necessarily a Hemi pickup. A Hemi pickup is 1/2” dia and the block would have to be drilled out to fit one. If it was a high pickup you would probably lose oil pressure at high speed rather than at idle.

 

[dvw]

The oil level will never be higher than it is at idle. Therefore I dismiss the pick-up height being to high or level to low. Pressure is low at idle because the pump moves less volume at lower engine speed. Is the pressure really at zero? We don't know that without trying another gauge. I just helped a guy with a 390 Ford. Same issue. He swapped the gauge, problem solved. Thicker oil would only be the answer if oil temp is extremely high. I oubt that as well. So suppose it's not the gauge. You've swapped filter to a Wix. I would discount the filter as the issue. There is a possibility of the relief valve never closing all the way, though unlikely. Since it has pressure at speed I would also discount any galley plugs not seated or missing. There may be a lot of internal leakage, loose lifter bores, bearings. Or a rocker shaft loose? causing an internal leak inside the valve cover. If it passes all these tests I would put a high volume pump in it. But to be honest I'd bet it's the gauge.
Doug

 

[Don Frelier]

The oil level will never be higher than it is at idle. Therefore I dismiss the pick-up height being to high or level to low. Pressure is low at idle because the pump moves less volume at lower engine speed. Is the pressure really at zero? We don't know that without trying another gauge. I just helped a guy with a 390 Ford. Same issue. He swapped the gauge, problem solved. Thicker oil would only be the answer if oil temp is extremely high. I oubt that as well. So suppose it's not the gauge. You've swapped filter to a Wix. I would discount the filter as the issue. There is a possibility of the relief valve never closing all the way, though unlikely. Since it has pressure at speed I would also discount any galley plugs not seated or missing. There may be a lot of internal leakage, loose lifter bores, bearings. Or a rocker shaft loose? causing an internal leak inside the valve cover. If it passes all these tests I would put a high volume pump in it. But to be honest I'd bet it's the gauge.
Doug

Agree that's why I made the suggestion in post#2