Oil pressure on new rebuild

[rogers]

I have just got my new rebuild running. It is a '93 599 block, so no squirters. I did use the high volume pump meant for the oil squirt blocks. I know there is some controversy over using the squirt pump in a non-squirt block, but I had it bolted in before I was aware of all that.

So, when I got it all put together and started up the oil pressure gauge "pegged out". I put a mechanical gauge on the pressure switch extension hose and the gauge read about 80-85 at idle. After about 10-12 min of running the pressure dropped to around 25 pounds. I am running delo 15-40.

I am not terribly worried about the pressure, maybe I should be. I am a little curious about the large variance between the high and low pressures. I know there are others running this combination, what has your experience been? Can anyone shed some light on this? Why so much difference? Does it have to do with the ops extension? Thanks in advance.

[phantom309]

did you use a fairly gooey assembly lube? i,ve found that that will collect places when its cold fired the first time,. give a high pressure reading,
I change the oil after 1/2 hr of gentle running with light load,. and then i see how things are,.
85-25 is a big swing,..but see how it is with fresh oil,..

jmho
Nick

[Robyn]

I used the HO pump on my DaHoooley rebuild. The pump came from a 506 Block that was in the rig and had fairly low miles.

I used a 929 Non squirt block. Bearing clearances at .0025"
Cold the pressure runs about 75-80 pounds and once the engine is good and warm and the oil is hot it will idle at about 30 and run down the road at 55 pounds at RPM's above 1500

This is fine and quite acceptable.
If your pressure falls to 25 and does not come back above that at speed I am ????? the reason.


Missy

[rogers]

If your pressure falls to 25 and does not come back above that at speed I am ????? the reason.


Missy

No, sorry, I wasn't clear. The oil pressure drops to 25 at idle but it does respond to engine rpms. I am not sure what it is down the road as she isn't rolling just yet. My main concern is just the big swing. Before I pulled the old engine I would see about 40 pounds cold and 20 hot both at idle, a difference of only 20 pounds. But with the rebuild there is a difference of ~60 pounds. It seems that is about the same as you see on yours right, Robyn? It just makes me glad I stuck on one of Kennedy's oil pan heaters, I guess.

[jerry598]

My experience after 400 miles on my current rebuild is the same as Robyn's. Oil pressure with the high volume pump pegs at 75-80 cold, then gradually goes down as the oil heats up, finally settling in the same ranges that she describes in her post. My only concern is with the OEM oil cooler lines. Hope they can handle the pressure because I did not do the upgrade to braided steel lines like I should have.

[rogers]

Cold the pressure runs about 75-80 pounds and once the engine is good and warm and the oil is hot it will idle at about 30 and run down the road at 55 pounds at RPM's above 1500


Missy

Robyn, Jerry, are these the numbers that you are seeing on the factory dash gauge or on a gauge tapped into the ops port? My numbers are from the mechanical gauge in the ops port, but my factory gauge is showing about the same as your saying.

Nick, I did use STP (as per the local race shop) to pre-lube the lifters and gears and whatnot. I will see what it does after the oil change. Thinking of running a 5-40w or even 0-40w oil after break-in, temps here never get above about 85*F(29*C) and very rarely below about 10*F(-12*C).

[Robyn]

I checked mine with a mechanical gauge and the numbers are similar to what the dash gauge reads.

The wild swings are due to the fact that the oump used on the squirt block is a HIGH Volume pump and not a high pressure.

Once the internal loss in the engine is exceeded by the pump then the pressure can climb.

The HO pumps are designed to be able to take care of the Huge amount of bleeding from the squirt nozzles.

On a cold engine the pressure relief valve comes into play and the excess pressure dumps off until the oil warms up.

At Idle cold mine will show about 75 PSI.

The cooler lines should be able to handle these pressures fine.

80 PSI is certainly not a lot of pressure.

Robyn

[DaveBr]

Scenario # 1 - I am not familiar with the 6.5 oil pump so I don't know if it has a spring loaded relief valve built into it like other GM pumps do. If it does it sounds like it was stuck close on start up and now it is stuck open which would explain the little to no variation in oil pressure.

Scenario # 2 - I rebuilt a 2.2L for my son's Sonoma. Local machine shop did the block prep & rebuilt the head. I did the build and put it in the truck. Started it up and it ran fine. Maiden voyage and lost all oil pressure. Towed it home and stuck mechanical guage on. 0 presure at idle and would rise to 3 psi when reved. Upon investigation I found a plug in the end of the oil gallery that had a small squirt hole for supplying oil to the timing chain had blown out. The machine shop didn't press it in properly. I don't know if the 6.5 has this type of system or not. Never been inside of one. If this helps...great. If it doesn't...just right it off as an old mans rant.

[Robyn]

The pump on the 6.5 is about the same as a BBC and a SBC oil pump.
They have a spring loaded plunger that pops out at around 80 PSI and dumps the excess pressure back to the sump.

These things will peg at around 80 PSI cold with the squirt block pump on a non squirt block.
Once the oil heats up and thins out the pressure will drop off to about 30 give or take at idle and run at about 50-55 at RPM

The wild swing even at operating temp is due mostly to the pumps ability to supply far more volume than the thing bleeds out internally.

A squirt block is an absolute fog of oil being sprayed around.

8 nozzles all squirting a stream of oil up into the piston crown.

These nozzles represent a very large internal leak and this is the reason for the much larger pump.

The pumps can be swapped from a squirt block to a non squirt block but not the other way.

A standard non squirt pump on a late squirt block will see oil pressure fall to near zero once the oil warm and barely keep any pressure when RPM is up above an idle.


All in a days work.

Missy