I've finally put about 1500 miles on my rebuilt-bottom-end LT1, which included a high-volume oil pump. (Not my choice--I would have probably stuck with standard volume and pressure.) Break-in oil was 30wt, which got changed out at about 30 miles. Next was 500ish miles of Pennzoil conventional 5W30, followed by 950ish miles also using Pennzoil 5W30, using an AC Delco PF52 filter (NOT the PF52E).
I have an F-body gauge cluster with the sensor harness modified to make the oil pressure gauge display actual oil pressure, not sit at 50psi or whatever. It reads 0psi and 80psi, with unmarked notches at 1/3 (20 psi?), 1/2 (40 psi?), and 3/4 (60 psi?).
With the 5W30, oil pressure would be about 65-70psi on cold start, run ~75psi during gentle cold warm-up driving, run ~40psi at idle while hot, and run ~60-65psi during hard acceleration when hot. Blackstone said that the 500ish mile sample tested out as low 30wt or high 20wt, so presumably the 950ish mile sample, which I just took tonight during the oil change, will also be slightly out of grade.
What I've noticed is that sometimes the oil pressure gauge will drop when I expect it to climb. Let's say, for example, I'm cruising along and oil pressure is at 55ish psi. Sometimes, when I accelerate briskly, as in 1/2 throttle or so and the car downshifts to second gear, I'll expect the oil pressure to climb to 60+psi, but the gauge will drop to 50ish psi during the acceleration. After I let off, gauge behavior returns to normal.
Tonight, I switched out the Pennzoil 5W30 for Mobil1 0W40 and a Mobil1 M201A oil filter. Since the LT1s are generally known for lowish oil pressure, and since in my Mustang Cobra, the Blackstone analyses look better running 0W40 instead of the factory-recommended 5W20, I have been running 0W40 in my Caprice and in my ~160K-mile bone-stock Roadmaster (which I know longer own). (Also, my wife's GL450 and my M5 both take 0W40, so it's convenient only having to stock a single brand and weight of oil.)
During a brief 10-minute test drive after letting the car idle a bit to warm up and circulate the new oil, I noticed that the oil pressure gauge seems to run 5-10psi higher than before. That's expected. I haven't seen cold start PSI as the engine was still warm when I did the oil change. But I did notice the oil pressure drop under acceleration more consistently--pretty much every time I'd get on it, compared only part of the time while running the 5W30.
My guess is that oil pressure is climbing beyond the oil filter's bypass range, and it's opening to let oil bypass the filter. I don't think that going back to 5W30 (Mobil1, not conventional oil, since break-in is done) will necessarily help, since the conventional 5W30 seemed to periodically activate the bypass, and since synthetic 5W30 is much-more likely to hold its viscosity over the duration of the planned 5K-mile oil run.
Is this something I need to be concerned about? Or should I not worry about it, since the filter's bypass opening (assuming that's what's happening) is keeping the oil pressure within an acceptable range?
I have an F-body gauge cluster with the sensor harness modified to make the oil pressure gauge display actual oil pressure, not sit at 50psi or whatever. It reads 0psi and 80psi, with unmarked notches at 1/3 (20 psi?), 1/2 (40 psi?), and 3/4 (60 psi?).
With the 5W30, oil pressure would be about 65-70psi on cold start, run ~75psi during gentle cold warm-up driving, run ~40psi at idle while hot, and run ~60-65psi during hard acceleration when hot. Blackstone said that the 500ish mile sample tested out as low 30wt or high 20wt, so presumably the 950ish mile sample, which I just took tonight during the oil change, will also be slightly out of grade.
What I've noticed is that sometimes the oil pressure gauge will drop when I expect it to climb. Let's say, for example, I'm cruising along and oil pressure is at 55ish psi. Sometimes, when I accelerate briskly, as in 1/2 throttle or so and the car downshifts to second gear, I'll expect the oil pressure to climb to 60+psi, but the gauge will drop to 50ish psi during the acceleration. After I let off, gauge behavior returns to normal.
Tonight, I switched out the Pennzoil 5W30 for Mobil1 0W40 and a Mobil1 M201A oil filter. Since the LT1s are generally known for lowish oil pressure, and since in my Mustang Cobra, the Blackstone analyses look better running 0W40 instead of the factory-recommended 5W20, I have been running 0W40 in my Caprice and in my ~160K-mile bone-stock Roadmaster (which I know longer own). (Also, my wife's GL450 and my M5 both take 0W40, so it's convenient only having to stock a single brand and weight of oil.)
During a brief 10-minute test drive after letting the car idle a bit to warm up and circulate the new oil, I noticed that the oil pressure gauge seems to run 5-10psi higher than before. That's expected. I haven't seen cold start PSI as the engine was still warm when I did the oil change. But I did notice the oil pressure drop under acceleration more consistently--pretty much every time I'd get on it, compared only part of the time while running the 5W30.
My guess is that oil pressure is climbing beyond the oil filter's bypass range, and it's opening to let oil bypass the filter. I don't think that going back to 5W30 (Mobil1, not conventional oil, since break-in is done) will necessarily help, since the conventional 5W30 seemed to periodically activate the bypass, and since synthetic 5W30 is much-more likely to hold its viscosity over the duration of the planned 5K-mile oil run.
Is this something I need to be concerned about? Or should I not worry about it, since the filter's bypass opening (assuming that's what's happening) is keeping the oil pressure within an acceptable range?