Low oil pressure.

Richard Shannon

Here's my story..... just finished a total rebuild of my '71 360 AMX. Fired right up, adjusted timing, set throttle to 1800 and varied the RPM's occasionally with a few raps of the throttle for 15 minutes. Initial pressure was 60 or so(maybe from the Vaseline packing?) and then gradually decreased to 20 or so before shutdown. Changed oil and filter (Castrol GTX 10w40 and Fram). Next startup pressure tops out at 30-35 and raising the RPM's will drop the pressure to 15-18, even at 2500+. I had the bypass blocked off so I restored it and no change. I removed the new relief valve plunger, which seemed to be stuck slightly and spring and replaced with my old spring and plunger which I made sure had no burrs and the port was clean. Replaced the Fram filter with a Napa Gold. No change. It has what I assume to be the original timing cover but I put in new gears. Initially on startup it had a midplate (wearplate), so I took it out. No change. Bought a oil pressure tester and tied into sensor port. Same readings.....Autometer Phantom gauge is good. After startup and RPM increase brings pressure down to 17 or so, I can put it in gear which has no effect on the oil pressure UNTIL I put it back in park and the oil pressure will increase to 30 or so and stay there until you raise the RPM's again. Long story short....Timing cover or WTH???

jeepsr4ever

:idea: Richard lets assume the bearings are in great shape and you dont have any leakage anywhere. Sometimes worn lifter bores can play a role in this but when you mentioned used timing cover this tells me that it could be a worn pump cavity. Are you running a stock oil filter adaptor? Is the oil filter bypass plunger stuck open? Here is a list of things to check 1. Oil filter bypass (little plunger where the oil filter screw on) 2. Oil pump cavity (Cavity to edge of gear no more than .0045) 3. Oil pressure bypass (Bore should not be larger than .565) 4. Oil galley plugs (If you can access them check to see if they are tight) 5. Oil pickup tube (Too close to pan bottom will decrease pressure with RPM increase) Worst case scenario...new timing cover, removal of oil pan and new pickup tube. Best case scenario...worn oil filter adaptor Let us know what you find :-|

Richard Shannon

Everything internal is new and clearanced to specs. Yes, stock oil filter adapter. The oil pan is stock but was reconditioned and looks like new. I did not check the clearance between pickup and pan. :oops: Before the rebuild I did not have this problem. If anything, shouldn't I have more clearance between pickup and pan after smoothing it out? If it's not the pickup, will a worn oil pump cavity or the other three possiblities for sure cause the same decrease in oil pressure with RPM increase? Thanks so much.

jeepsr4ever

Most likely the oil pump cavity Richard. The others are distinct possibilities.

Richard Shannon

Much obliged!

jeepsr4ever

Good luck and please post up your results :sa:

1970amx

Another couple of things I could think of. the pickup tube cracked or not tight in the block...sucking air the pickup tube screen clogged with silicone or other debris from the rebuild the pickup tube screen and the sheet metal screen cover collapsed down onto the tube More than likely it is something to do with your timing cover as mentioned in the above post. If not the timing cover you have some clearance issues...a galley plug problem.....or a pickup tube issue ? Best of luck. Let us know your findings.

Richard Shannon

Thanks..... I'm gonna pull my oil filter adapter and check the gear clearances (0.0005-0.0025?). If they check out, I'll drop my crossmember and pull the pan and look for oil pickup issues. If that checks out I guess I'll be pulling the timing cover and tranny to check the oil gallery plugs. Anyhoo, thanks for all the help. I'll post what I find.

1970amx

Richard Shannon wrote
If that checks out I guess I'll be pulling the timing cover and tranny to check the oil gallery plugs. Anyhoo, thanks for all the help. I'll post what I find.

If the external oil galley plugs were loose or missing oil would be going all over the floor making a mess. The galley plugs to worry about if you don't have an external oil leak is the internal galley plugs under the intake manifold and behind the timing cover.

Richard Shannon

I do have an oil leak that drips off of the tranny bell housing. Maybe 20-30 drops each startup. I thought it might have been rear seal or pan gasket but all bolts are snug. Even dropped the starter to get to those pan bolts. I can't see where it's coming from. If it was inside bell housing that would explain why. It only leaks when running and for very short time after shutoff. Again I've gotta be honest, :oops: :oops: I know the gallery plugs were there, I just neglected to check for tightness. If they were just handy, could it cause such a drastic decrease especially with increased RPM's? Maybe the sum total of loose gallery plug(s), and worn timing cover cavity? I'm fairly confident about the oil pickup. ???????

Richard Shannon

I'm just gonna pull it back out and tear down. Easier to work on out of the car anyway. While I'm at it I've got a new timing cover, Torker and Eddy 800 to put on. That way I can check EVERYTHING. Thanks for all your help.