Losing oil pressure
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Losing oil pressure
To begin with, I had a 460 engine that would start out with good oil pressure when oil was cold and then the pressure would drop down to zero when warmed up. Not thinking much about it other than it was a tired engine... I bought another engine and have since rebuilt it from ground up. Now I have a brand new engine with the same problems... still a 460 block with all the new goodies.... it starts out with good pressure around 55 to 60 psi... then it warms up and drops down to zero. I am in search of some ideas as to why this is happening. I have an aftermarket oil gage and am taking the pressure reading on the back of the block behind the manifold where the stock electronic pressure sending unit used to be for my dummy light.
I am in dire need of some help... I have over 3 grand into this new engine and don't want to drive it without knowing if I am getting correct oil pressure.
I am in dire need of some help... I have over 3 grand into this new engine and don't want to drive it without knowing if I am getting correct oil pressure.
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Losing oil pressure
You may have already done this, have you put a different gauge on it? I'm understanding your hooking it up to the factory location. Right? There is deeper problems if you have established your gauge is correct. To much bearing clearence.
Senior User
Joined: Jun 1999
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Losing oil pressure
What type of oil are you using, I had a similar problem with my 390, using 10w-30, it would be fine when cool but when it got warm it would realy drop, but not to zero. I put in 30w and it has much better pressure. Also, hows your oil pump?
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Losing oil pressure
Yes, I have checked out the gage. In fact I have hooked up a pressure tester into the same port and came up with the same results. I was using the port behind the manifold on the top of the block in the rear... but last night I switched my connection to the oil plug port just behind the oil filter next to the fuel pump as I thought that would be a better place since all my books refer to that position. Same problem.
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Losing oil pressure
I used 30W oil which is supposed to be used during a break in. Also I had a brand new oil pump. After changing the oil gage connections and had the same problem I drained the oil and dropped the pan and replaced the standard oil pump with a new high volume oil pump. Still the same problem. I did notice something strange though... the 30W oil had completely broke down and was like water from the moly lube and all the other assembly lubes.... ???
Posting Guru
Joined: Sep 1999
Posts: 2,297
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From: Indiana
Losing oil pressure
Did you have the crank checked to see if it needed turned, and replace the cam bearings? Since you have covered the pump and gauge, it sounds like you may have to much clearance at the bearings, which can happen at the crank or cam. Your bearing clearences are tighter when the engine is cold then when it warms up the metal expands and there goes your oil pressure.
New User
Joined: Nov 1999
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Losing oil pressure
Yes, I did have the crank ground .010 and got the bearings to accomodate this... I also had new cam bearings pressed in... in fact the second cam bearing was so tight... or had a ridge... that I had to hone it to even get the cam to go in. I think I am to the point where I am gonna pull the engine this weekend and recheck all the bearings to make sure they have not slipped or that the oil ports are all ok... and also plastigage the journals again...
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Senior User
Joined: Jul 1999
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Losing oil pressure
While you have the engine apart... check the oil pump pickup carefully. Buy a new one if suspect as an air leak will cause low oil pressure. If there is an oil pressure relief valve in the block, check that for sure. I don't know much about the 429/460 blocks... the FE is my forte.
Best of luck TLC
Best of luck TLC
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Posting Guru
Joined: Sep 1999
Posts: 2,297
Likes: 1
From: Indiana
Losing oil pressure
BigRedTruck, that cam bearing you had to hone is probably where your oil pressure is going when it warms up. That bearing was a little bit cocked or something, you should never have to hone a bearing to get the cam in. My brother in law had an old Chevy 350 had the motor rebuilt, the cam wouldn't go in either ( new cam bearings ) well they honed a bearing or two to get the cam in , it was the same way , it never carried any oil pressure, he finally blew it up. We argued about it, I told him you never hone bearings, he said well the mechanic said it was OK. If you have a tight cam bearing replace it. I know that sucks , but it sucks worse when its in the vechicle.
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Losing oil pressure
Well to wrap up this dilemma.... After taking the engine back out and plastigaging the main journal bearings... it was found that the machine shop must have ground the crank .020 instead of the .010 as indicated by the return markings and request by me to have done. There wasn't any compression at all on the plastigage... so now that I have it out and tore all the way down again... I am going to have the cam bearings replaced and mic the crank and get the right size journal bearings..... Thanks for all the info and help to all those who replied.
Posting Guru
Joined: Sep 1999
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From: Indiana
Losing oil pressure
BigRedFord, glad to hear you got to the bottom of your problem, Like jowilker said its good you didn't hurt anything and did something about the problem instead of just driving it and ruining the motor. Good luck!!!
Guest
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Losing oil pressure
>BigRedFord, glad to hear you got to
>the bottom of your problem, Like
>jowilker said its good you didn't
>hurt anything and did something about
>the problem instead of just driving
>it and ruining the motor. Good
>luck!!!
sue
>the bottom of your problem, Like
>jowilker said its good you didn't
>hurt anything and did something about
>the problem instead of just driving
>it and ruining the motor. Good
>luck!!!
sue
Guest
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Losing oil pressure
New question arises... Do I go to .020 oversize main bearings (if they even make them), or do I take the old crank out of my old engine and have it redone? Problem I am thinking about is... if I go too much oversize on the main bearings... will they be too soft and wear out quicker? Thanks again!
Freshman User
Joined: Nov 1999
Posts: 33
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Losing oil pressure
Over the last few years I see more .020 under in the crank kits. I have used several and havent had a problem yet. I wouldnt want one in my own but I am pretty picky about my own stuff. If you use the motor normally you shouldnt have any problems. How did you buy the crank? Most cranks come in a kit, crank and bearings. If yours came in a kit and you got the wrong bearings take it back and ask for a labor claim. It happens.