We picked up a 400 sbc for my wifes 50 chevy 3600 after buying it with a cracked block 350. One thing after another with it. Today was supposed to be a day of glory. The sun is shining, its not too hot, lower than usual humidity. I fired it up cruised around for about 10 miles. Figured that was good and decided to turn around. I pulled into a parking lot to turn around and looked down at the gauges again. 0 psi on the oil gauge. I shut her down right there. Checked the oil and its clean and full. I fired it back up with the hood open and I could see oil being pushed through the plastic oil line going to the oil gauge. I reved it up, oil pressure came up. I headed home. At 50 mph I was making 25 psi of oil pressure the whole way home - I don't know what the rpm was - no tach yet. Fresh oil, 10w30 or 10w40 i dont remember, Wix oil filter, 60 psi of oil pressure at cold idle. I plan to put some 40w oil in it and hope for the best. This is not a fresh engine and I have no idea how many miles are on it but I assume its going to need some bearings shortly. I had to do the rear main seal and while I was there i checked the torque on the mains and rods just because. Is there anything else I should be looking for or at?
When you pulled the rear cap did you see copper? What RPM were you at at 50mph - The "0" reading could have had something to do with inconsistent pressure or a "kink" in the nylon line - I generally use copper - run 20/50 and keep an eye on it
Sounds like what the above member stated. I've never used the plastic oil pressure tube after seeing the mess in a friends car over 50 years ago. Copper or have a flexible hose made. Is the oil pressure gage an aftermarket piece?
According to a gear calculator online I should be at 2000 rpm at 50 mph. I also checked for kinks, I wrapped it nicely and verified it was still nicely wrapped. I have a copper line to replace the plastic soon. Pressure readings are hooked to a known good mechanical garge. I'm glad you said that because I ended up getting 20/50 instead. I'll do the oil change and see what happens when I get home. Edit: no copper or foreign metal when I pulled the pan. The pickup tube was also nice and clear
Make sure to use Oil with Zinc! Oil pressure created by Clarence's on bearing, Rule of thumb Is 10 Psi per 1,000 rpm's So @ 1,000 @ least 10psi , @ 4,000 rpm's = 40 psi, As temps from Cold to Hot oil pressure will drop after warm up & should hold steady @ Idle . Weights of oil to use there are more factors to understand , Do not see where you are @ 20/50 year round , some times in Hot / Summer Straight , 30,40,50 . A Oil that sorta commonly available but getting hard to get on shelf Is Silver colored container is Valvoline VR1 None Synthetic
The bearing itself would be copper when there is excessive wear - the outer babbitt wears off creating excessive clearance
I put the 20/50 ZR1 in it and drove it around. No difference. Cruising around around 40-50 mph my oil psi was holding strong at 40-ish psi (50mph is 2k rpm, I have no tach). Once she was good and warm i came to a stop sign... right back to 0 psi. Idle rpm is set by ear and I'm guessing its around 700 rpm, its smooth and happy. The whole time its at 0 psi I heard no clatter, no strange noises, no nothing. If it wasn't for the gauge I honestly wouldn't have a clue I was having oil issues. I'm just about to the point of this truck I'm done for awhile. I've pushed and pushed to get her dialed in and its cruising, running, stopping pretty good. Its been a nightmare of a build. Just when I get one thing its another. I may just park it for awhile, my wife as pretty much lost all interest in her truck at this point.
Screw a mechanical gauge into the port and check pressure. You could have a bad sending unit, bad gauge or bad ground.
Having forty psi at cruse speed, then drop to zero at idle, sounds like an oil pump with too much clearance or pickup that's loose and sucking air. Forty psi at cruse speed seems too good for having bad bearings...?
Just saying , rule of thumb 10 per 1,000 Check with another gauge , I dove one for 10 yrs a wore out 350 @ 5 psi @ idle ,Hot Down road @ 45psi ... No noise good sign, Cut open oil filer & see what in side , There are 40k plus engine 10 psi @ Idle. Try straight 50 or 60 , even 70 if your Not comfortable Not winter weights thoe below 50 deg
I would like to see at least 10 psi at idle and 40 - 50 at highway speeds. A hail Mary would be to replace the oil pump. Don't do a high volume/high pressure pump, just a stock Chevy oil pump. That's all I ran in the sprint car and never had any trouble. The pickup tube on a SBC is a bear to get into the pump. If I changed the pump I would use the top and pickup off the old pump as long as the top wasn't scored.
If end plat Scored , Block sand / file To reset Clarence's, same with gears , Some times best to spend $ 30 plus On new pump , cheap pumps should be checked now a days .
I pulled the filler cap and pcv valve while the motor was semi warm - making 20 psi at idle still. There is hardly any oil making its way up to the heads. How the roller rockers are not making noise i dont understand. I figured 20/50 should be thick enough that if I was onto something it should show on the gauge. After pulling the filler and seeing the lack of oil I believe the gauge. If I had 10 psi at idle I would have never started this thread. I want to think I have a bad pump but making good psi cold tells me I may be wrong. I think at this point is the general consensus is to change the oil pump that's what I'll do. I did look everything over while I changed the rear main and it seemed in reasonable repair. I dont want to believe this motor is crap! It runs so damn good! Warm but good!
OK but it can still be defective. Try another one. They are cheap. The reason oil pressure drops can be threefold. It can be a worn out pump (excessive clearances), it can be a faulty relief valve in the pump (not seatingg or sticking or bad spring) or it can be excessive clearances. If the clearances are not tight, the oil flow doesn't have enough resistance to create pressure. If that's your problem, a new pump won't help.
As said, try another gauge to confirm. You can pull the dist. and use a drill to drive the oil pump and check pressure and flow that way without diving into the engine or continuing to run it. If it doesn't develop pressure and/or doesn't oil the top end, you are going to have to swap again or dive in. BTW, this is standard SBC stuff. Having 400 in the title might get this bumped into the OT section.
Ill grab a new oil pressure gauge tomorrow. I pulled one of the valve cover off and started it cold. Oil pressure on the gauge showed 60 psi. Oil flow to the valve train was minimal at best. Just enough that the roller rockers are sort of lubed. I'm guessing the oil pump is bought is wasted money and my bearings are gone.
If "WE" want to learn how a SBC's oiling system works, the issues that are posted, and possibilities.... First pressure spike will be at the port in the back of the block= OPSU/Gauge! It will read high right out of the gate. Now- there's cold oil=thicker to show more pressure.......... Warming up, it get's thinner........ HHmmm. RPM will spin it faster, but the oil is getting hot, and thinner...... Possibles, and not discounting, because iv'e seen some goofy shit. Gauge= Doubt it, because it showed higher pressure when cold, then fell off. Plugs missing? naw....... Oil pump? Possibly ....Colder oil being thicker=fill's the gaps if worn........ Last 400 was in like 74/75? Worn/used engine with no history? No mention of death smoke/oil consumption, death rattle, etc...........=Engine is worn, and bearing clearances are shot......
Sounds like clearances on bearings at outer end of limit. Had that discovery on 2 small blocks I've been in to.
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