Losing Oil Pressure 505

[Schober Motorsports]

Hey guys... I got a weird one for you.

Got my engine back together after the last block cracked. All new rotating assembly, mains are .002 Full Groove and rods are .0022-.0024. All the plugs on the inside of the block are plugged to include the 3/8 stock pickup as I am running an Milodon external line. Here's my issue. Broke in the cam yesterday, got about 12 mins in and started loosing oil pressure and I shut it off. Was at a solid 80 psi and it started dropping and dropped to 20psi at 2500 rpm so I shut it off. Checked oil pump driveshaft, that had not been broken. I put my drill into it and it came up to 80 psi... Next day I put it all back together, fired it up and its back to 80 psi. After a little bit and the motor got warm, it started dropping again. This time to 40 psi. When you hit the throttle it goes down in oil press psi and has a real hard time recovering... Its a brand new Mellings HV pump w/ Milodon cover & -12 AN fitting to the pan. The pan is from Milodon as well and is one of those 7 qt pans with the pickup tube built in. I also changed the oil filter w/o change.

Any ideas? ...Thanks

 

[451Mopar]

I'm thinking either the pickup is too close to the pan bottom, or maybe the oil is getting aerated?

 

[Hemirunner]

Is the bypass sticking when it gets to temperature?

 

[Schober Motorsports]

Pan is a Milodon 31581 with the pickup built into the pan. Wondering if it is too close from Milodon OR that the baffles in it is not allowing the oil to get to the sump? Either way its 7 qts.. I changed out the relief valve twice with new units without change. Aerating in the oil is a possibility, need to check and see what the oil looks like. For it to loose oil pressure w/ RPM sounds like it.

 

[Fran Blacker]

Is it possible the shaft spins inside oil pump rotor or is it pinned? Not much chance of this but possible. You would think when cold it would happen.

 

[Hemirunner]

I'm thinking either the pickup is too close to the pan bottom, or maybe the oil is getting aerated?

Or drainback issues, or pickup hose sucking shut (not likely if new) or too little oil, I’ve seen all kinds of issues with those aluminum covers, even warping. The aluminum pump bodies are really horrible. One was so warped, it would lock the pump up when you tightened the bolts.

 

[NSS Guy]

any chance it pumped all the oil to the top end and is not draining back fast enough? do the heads have external oil lines with restricters?

 

[Schober Motorsports]

Heads are 270 Trick Flow's. I was told that they were already restricted and that no further would be needed. I took off the pump cover, saw no signs of the rotors from the pump beating it. Saw just light skid marks that were very very fine. Here's a picture of the pickup hose, I don't think its that major of a turn, but would it be enough for it to collapse and start slowly loosing pressure?

 

[RT K_line]

Is that hose new? Maybe collapsing internally. Just a thought!

 

[Schober Motorsports]

Yes it is new, I put the hose together last night

 

[IQ52]

Yep, it really sounds like the rubber inside the hose is blistered and sucking closed. Those symptoms are exactly what I had when losing oil pressure like that on that damn 528 hemi.

 

[Schober Motorsports]

What do you guys suggest as far as replacement? Build another hose? Go with an aluminum hard line?

 

[dvw]

As a test add a qt of oil. If it's not returning that will help. What is the oil temp? It's either temp related (to much internal clearance causing internal leakage when oil warms), lack of oil in the pan, Lack of liquid oil feeding the pump. How are you feeding the rockers? Bushed lifters?
Doug

 

[IQ52]

What do you guys suggest as far as replacement? Build another hose? Go with an aluminum hard line?

If it is an internal blister, you should be able to see deformation on the internal wall. If so, I'd replace it with a teflon lined hose.

 

[bearman]

What do you guys suggest as far as replacement? Build another hose? Go with an aluminum hard line?

hard line everything you can. have seen hose fall apart from inside to many times.

 

[dsd1967]

Also come out of the bottom port with a 45 degree hose fitting or adapter to reduce the hose bend radius. The hose blistering may not show up unless at temperature. If that is a pickup line you may have vacuum exacerbating the problem. In any vacuum situation make sure the hose is rated for it. Even Teflon will collapse under vacuum unless it has an internal support coil.

 

[Schober Motorsports]

Here it is... External line blistered up on the inside. Thank you all for the help, so heres the question... Is it the oil temp that caused this, too much of a turn in the hose, OR was it a defect in the hose itself? I was unable to find any hard line tubing in -12 out there, maybe I'm typing in the wrong info, but I sure have seen it before. I'd much rather go hard line and never think about this again. Either way in running an inner support the second best option?

 

[dsd1967]

Tubing should be readily available. Check McMaster Carr. Get seamless tube so you don’t have to double lap flare.

 

[bearman]

make your own hard line. as for the blister in the hose could be many different sins that caused it. what is oil temp running and do you have a oil cooler on it.

 

[bearman]

where did you get the hose from and what was the hose rated at temp and pressure. for the most part blisters or flaps are from twisting the hose and heat.