Lower oil pressure

[Mike Bartlett]

I just started my 427 S/O after installing new heads/intake, rings, rod bearings. Prior to this rebuild I was running about 25-psi at idle and about 60-psi at 2500 rpms. Now at idle I am about 10-15 psi and 40-45 at 2500 rpms. I am using the same oil pump, pan, etc. I did change the thermostat from 180 to a 195 which obviously increased my operating water and oil temp to about 195F-oil/205F-water. I am using Delo 15/40 oil but ran out at 8-qts so I added 2-qts of 5/30.

Any thoughts? Are these new pressures acceptable? I will try maybe 20/50?

Thanks,

Mike

[Scufty]

I dont know that I would have mixed the 2 oils but thats not the issue ...how bout your oil lines? All hooked up correct? Maybe dumb question but wrong hookup of remote lines has led to alot of wrecked engines

[lineslinger]

Too low, what kind of oil pump are you using and is your pressure relief valve working? Maybe stuck open?
Mixing oils for a pressure check is kind of counter productive, although yours truly has done the same thing in a pinch, now you have a bastardized mixture which won't want to replicate, I assume.

[olddog]

What is the rod bearing clearance and how did you measure it? What was the clearance with the old bearings?

[Mike Bartlett]

Not sure what type of oil pump but it only has 2800 miles on it and is the same one I was using before when I had the higher oil pressure. I did not remove any plugs, oil springs, etc. I can't remember but where is the oil relief spring located? Possibly in the rear behind the bellhousing in a nice convenient place?

I measured the crank journals with two different calipers and they measured out to be stock size, can't remember the size right off hand. I also read the old rod bearing numbers and since it appeared my crank journals were stock I ordered the same size rod bearings as the old ones. CLE-CB760P standard size Clevite from Summit. I did not measure the actual clearance as I probably should have but I figured if the journal size is stock, or so it appeared, then all I need is stock rod bearings?

I plan on hooking up another gauge to a different location to double check my pressure. Isn't their another spot somewhere near the oil filter area on the block? If another gauge reads the same I'll try thicker oil.

-What would be acceptable pressure at idle?

Any other suggestions?

Thanks,
Mike

[c6ae]

It sure sounds like you have a clearance issue. At this point I would at least drop the pan and use some plastigage to rule this out.
Calipers are not accurate enough to measure a crankshaft for clearances.
In the standard sizes, bearings were/are available in.001 and .002 undersize to take up for normal wear or initial clearance deviations and the marking of these may be not be immediately apparent. Is it possible that your engine had these bearings?
There is also a 427 specific rod bearing that has more clearance built in (.0005 thinner shell) but I don’t think these are still available.
You shouldn’t rule out the relief valve located in the pump, it might have some debris lodged causing the relief valve to stay open. This would give similar readings on the gauge to what you describe.

[MaSnaka]

My understanding is the plasti-gauge is only accurate if the engine is inverted so the weight of the crank does not factor into your reading. John

[c6ae]

When gauging the mains in the car the weight of the crank could give a false reading. A folded piece of paper (about .006) used as a shim on an adjacent journal to lift the crank up will eliminate this error. I usually only undo only one or two main bearings at a time being extra cautious at the ends; otherwise damage to the seals could result.
I have found plastigage to be a very useful tool, and pretty darn accurate. It seems to take a fair amount of pressure to get a true reading, i.e. I retorque the caps. It certainly won’t ever replace micrometers and bore gauges, but it will give you a clue whether or not you need to tear it apart...

[48 IDA]

Mike,
Change the oil using the same as you used before your ring, and bearing job.
Check the oil pressure and compair to your reading at that time. Then if
there is a pressure change, I would start looking for problems. Keep it
simple.

Good luck

Don

[RedCSX1]

Mike,

My motor has less than 1500 miles on it and its been out twice. Inspected and replaced with new pump from Precision Oil Pumps both times. Just good insurance before you bolt everything back together. I would drop the pan and replace the pump. Also I run Shell Rotella oil and have been real happy with it. My oil pressure looks like this:
Cold oil pressure is over 100 lbs, warm 35-40 at ilde (1100 rpms) running 65-70mph 75-80 lbs.

[olddog]

Another point. I have read where some builders will hand polish rod journals and end up with slightly different journal diameters. They then measure each journal and each bearing and put the tightest bearings to the smallest journal. I have heard of people mixing bearings, where one journal my be standard and another 0.003 under.

It is best to measure each and every bearing and journal, as you never know what may have been done in the past.

[Philip Messer]

Mike,

Similar problem in my Ford Racing stroked 351 Windsor with 2000+ miles on it. I live in sunny Phoenix and my BDR Cobra has an oil cooler. With 30 wt oil at normal operating temp, I ran 25 psi at idle and about 55 psi at 2000 rpm. The engine sat idle for six months while I was making reapirs to the body. Upon restart, I installed a new filter and added 5/30 wt oil. I primed the engine by cranking the oil pump, not the engine with the starter. At normal operating temp, the oil pressure dropped to 15 psi at idle and 40 at 2000 rpm. I also noted a valve or two clanking at idle when the radiator fans kicked in (at 93 C). So, I drained and flushed out the 5/30 wt oil and replaced with 30 wt oil. Now when the fans kick on, I have 25 psi at idle and about the same 55 psi at 2000 rpm (back to the original pressures).

So, I would take Don's advice and drain out that 5/30 wt oil and replace with with new oil of like kind that was in the engine prior to your internal work. If you are 20 psi or above, you should OK. I would not feel comfortable with oil pressure at idle much less than 20 psi. (There are past threads dealing with oil pressure. You should review them.)

Good Luck. I will keep my fingers crossed for you!

Phil