Can anyone explain this oil pump problem?????

[Longhorn Man]

OK, yesterday I lost all oil pressure in the caddy motor. ( http://67-72chevytrucks.com/vboard/s....php3?t=144642 ) I know it happened, I have a witness. (I was actually starting to wonder if I saw and heard what I had thought I saw and heard)
Well, I go out there today to grab some parts out of the box that I had bead blasted for a buddy of mine. I don't really know why I did it..but I hopped in and fired it up.
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40 psi of oil pressure.
I got a PM about a plunger that can get stuck, and I'll be looking for this tomorow (or thursday..when ever the parts get in) when i rebuild the pump.
Even so, it's still enough to make you crazy...or at least wonder if you are crazy.
40 PSI with thick sub freezing oil (10w30) isn't really much to brag about, but it is better than the 5 psi I was getting at 4000 RPM yesterday.

[Longhorn Man]

oh yeah...there was a question involved here....WTF, anyone ever seen this?
Like I said, there was a PM about a plunger...and he was speaking from experiance...any other things to look for?

[Sonny]

Was the motor OK? Knocking gone we hope?

[69 longhorn]

the pump has a releif valve, if it sticks, you can blow the can off the filter......or have no , or very low pressure. I have seen irratic pressure @ idle with a sticky releif also. you should be able to get at that bypass pretty easily on that Cad(1 pluss on external pumps) best of luck ......69L

[stllookn]

Andy, What year Caddy is the motor. I will look in my old Chiltons on GM engines to see what it says. 1967-1974 Chiltons with the Cadillac motor info if it will help.

[Longhorn Man]

the engine is a 77 425 out of an eldarodo
Al...This is now 2 ppl saying they've seen something like this and it be that valve/plunger. Sweet. I like the sounds of that.
Oh, yes, Sonny asked the most important question, and yes, the knocking was gone. I drove the truck across the lot, I didn't want to get into it [i]too hard[/ii] but I did get 2500 RPM and held it there for a moment as I shot across the lot.

[stllookn]

Andy, I guess only the '67 oil pump mounted under the front engine cover. Later models mounted in the pan just like the rest of the world. External pump relief spring is to measure 2.77 to 2.84 inches. 2.77 to 2.89 in '68 and 2.57 - 2.69 for '69-'73.

[stllookn]

Andy, The oil pump relief valve is a good guess.

[Tx Firefighter]

I've seen sludge get sucked up onto the oil pickup screen under hard running, then fall back out of the way when the engine shuts off.

[Harold Shepard]

I had something similar happen with a non cad motor. 72 chevy 350 running the snot out of it oil pressure went away knocking the whole nine yards, shut it down and left it where it stopped. Went back the next day, it had oil pressure and knock was gone- until it got warm then reappeared and even tried to seize the crank- long story short- spun main bearings and a couple of rod bearings. I would pull it apart to be sure before I bet on a stuck plunger in the pump, gaskets are cheap vs. machine work. Just my .02 Harold

[CHEVIBUBBA]

gm recommends a minimum of 5 psi at idle.but at 4k rpm?
bet you wiped a bearing.

[72402]

I saw this happen on a Caterpillar engine one time after it had been rebuilt. It had a shop towel in the oil pan.

[Longhorn Man]

many good points here...
the sludge factor was minimum, and I cleaned out pretty much all of it. While i am sure there is a bugar somewhere...I doubt it. I was really annal when i was cleaning up the engine.

[69 longhorn]

Originally Posted by Tx Firefighter

I've seen sludge get sucked up onto the oil pickup screen under hard running, then fall back out of the way when the engine shuts off.

I have also seen chunks of nylon, from the stock cam gear in the screen do the same trick......go for the easy chit 1st, & hope for the best(a very sharp old man taught me that....my Dad ) best of luck Andy.... L

[Brainchild]

Well I guess I'll add that I have seen silicon get up in the pump and shut off oil flow,of course it was Ford,so it may not apply

I also heard that an engine needed 5psi for every 1000 RPM.Don't know if that's true or not.

[VetteVet]

Hey Longhorn I put this on the other thread and meant to on this one so You got both of them. It's a pic of an AMC oil pump but shows the basics.
Vettevet-- hope she ain't hurt

[Longhorn Man]

Brain child...that actually supposed to be 10 psi per 100 RPM.
Vet...thanks. The Caddy pump is something like that.

[Tx Firefighter]

Originally Posted by Longhorn Man

Brain child...that actually supposed to be 10 psi per 100 RPM.

No way Andy, that would be 100 psi at 1000 RPM (virtually idle speed).

[COBALT]

Besides nylon from the cam gear could debris from the oil filter or your timing chain cause this too? I was just wondering what oil filter and timing gear you had - anything that might float around in your oil journaling system and hang up that relief valve, but would be soft enough not to sieze up the gears in the pump.

Just brainstorming...

Could the spring in the relief valve get brittle and break? I doubt it.

[busterwivell]

He meant 10 per 1000. I hate to bring it up Andy, but I had one that had decent pressure till it warmed up, then went to 10 lbs. The bearings were shot. Hope that's not the case with you.

[GMC AMI]

Oil tube pick up seal? Thin seal that goes between block and pick up tube. Did you get the right distance for the pick up screen clearance? Too close to the bottom of the sump will slow down the oil flow at 4000 rpms easy enough for the pump to out pump the restricted supply of oil and lose oil pressure.

[71cadc10]

Andy,

Did you pull the front cover and replace the timing chain and gears before you stuffed this in?
The nylon tipped cam gear I'm pretty sure was gone by early 70's so your 425 shouldn't have had one of those. If you pulled the pan and cleaned it you would have seen the floating pieces of nylon at that point. They will clog up the pickup screen and could give erratic oil pressure.

I too lean towards bearing issues, cold oil will cover that problem up. Start it back up and run it till warm and see if it holds pressure after warmed up.
A stuck bypass in the pump is a good option though. just being a pessimist here.
Or this could be an omen to put a 500 in it !!!! Quit playing with the little 425...LOL.

[dtlilly]

2 opinions and experiences:

1. I had a 94 Mustang GT with 163,000 miles on it. About every 1000 miles I would have to drop the pan and replace the oil pick-up tube that was clogged from gunk. The motor would clank, clatter and knock with no oil pressure until I changed the tube and pick-up filter. I changed the tube one last time, sold the car and bought the 71 GMC 4X4 that started me on this old truck kick.

2. You were running the truck harder than a virgin on prom night. The oil got hot and lost viscosity (turned to water), then when cold and thick again, it worked fine.