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Old 03-13-2009, 07:01 PM   #1
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Newly rebuilt engine - LOW oil pressure!

Hi, first off I have a newly rebuilt 350sbc. New cam, new gaskets, new oil pump, new everything really. Had a professional shop build it.

My problem is that when I had the same shop put this engine in the car and fire it up for a test run/break in, the oil pressure is very low, dangerously low. I tried a different gauge, and then a third, but the reading is the same on each. Barely any pressure. My question is what could cause this?

Thanks in advance
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Old 03-13-2009, 07:02 PM   #2
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Re: Newly rebuilt engine - LOW oil pressure!

There's really only one way to find out. That's to tear it down. Was the crank turned and matched to new bearings?
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Old 03-13-2009, 07:14 PM   #3
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Re: Newly rebuilt engine - LOW oil pressure!

Well I suppose I won't be of much help seeing as I wasn't the one doing it, but since this shop has been in business for over 40 years I assume they did the right things , but again I don't know. You're saying there's nothing small they might have forgotten to do that can be fixed with the engine in the car? It will have to come out and gone through?
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Old 03-13-2009, 07:20 PM   #4
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Re: Newly rebuilt engine - LOW oil pressure!

you have to learn to only have machine shops do the machine work.then check everything they did and put your engine together yourself.because they will not take any blame.i've found this out the hard way
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Old 03-13-2009, 07:32 PM   #5
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Re: Newly rebuilt engine - LOW oil pressure!

First, what are you calling low? Until about 2 years ago, GM's 502 crate engines typically shipped with a hot idle oil pressure around 10 psi. Not a problem, just less than most are used to. If you're above this, and your pressure increases with rpm, then try straight 30-weight oil.
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Old 03-13-2009, 07:33 PM   #6
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Re: Newly rebuilt engine - LOW oil pressure!

Well it's under warrenty so it's all free. I was just hoping to not have to wait another week
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Old 03-13-2009, 07:35 PM   #7
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Re: Newly rebuilt engine - LOW oil pressure!

under 5 psi
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Old 03-13-2009, 07:37 PM   #8
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Re: Newly rebuilt engine - LOW oil pressure!

And there's no puddle of oil under the engine?
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Old 03-13-2009, 07:39 PM   #9
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Re: Newly rebuilt engine - LOW oil pressure!

no leaks, clean as new
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Old 03-13-2009, 07:42 PM   #10
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Re: Newly rebuilt engine - LOW oil pressure!

Unbend a coat hanger, mark off 10 inches. Remove the oil pressure sensor at the rear of the intake manifold, and insert the coat changer. If you get all 10 inches into the block with no effort, then a critical plug was left out. You shouldn't be able to slide 9 inches in. Youre sticking it in vertical.
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Old 03-13-2009, 08:03 PM   #11
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Re: Newly rebuilt engine - LOW oil pressure!

thank you for the comments, I'll be trying these things tommorow and try to diagnose the problem myself
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Old 03-13-2009, 08:19 PM   #12
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Re: Newly rebuilt engine - LOW oil pressure!

There are also 3 plugs in the front of the block behind the timing chain gear. Left and right are the lifter oil galley plugs, center is the main oil galley plug. If you're missing the left or right plug it'll read low. If you're missing the center one it'll barely build any pressure.

Many shops convert these plugs over to threaded plugs when they do the other machine work (so they can't fall out). Otherwise they are just cap plugs retained by a tight fit when hammered in place (which can fall out if the stars align just right or weren't installed correctly to begin with).

The plug that Atilla mentioned at the rear about 9" down in the block is important becuase it's what forces the oil to go through the oil filter (as opposed to bypassing it) but it won't affect your observed oil pressure much.
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Old 03-13-2009, 08:30 PM   #13
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Re: Newly rebuilt engine - LOW oil pressure!

Damon is mostly correct. But if the plug I told you about is missing, then that would tell you something about the machine shop. However, it also can turn an acceptable-though-not-ideal 10 psi at idle into 5 psi. Yes, it can be a 5 psi drop. Less restriction, and loss of 4 90-degree turns, each can be 1 psi difference. Also slightly easier to fix, and running the engine with one of those other 3 plugs missing will be more likely to ruin bearings, etcetera.
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Old 03-13-2009, 09:55 PM   #14
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Re: Newly rebuilt engine - LOW oil pressure!

Good information, thank you for all your knowledge.

I'm confused by the fact that plugs could let the pressure drop but not let all the oil flow out onto the floor?? If a plug were missing wouldn't the engine leak oil?

I'm not physically with the car/engine so tomorrow I'll be able to post back and have a better idea of what's wrong.
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Old 03-13-2009, 11:03 PM   #15
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Re: Newly rebuilt engine - LOW oil pressure!

They're called internal leaks. The machine shop can show you when they find where they slipped up.
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Old 03-13-2009, 11:17 PM   #16
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Re: Newly rebuilt engine - LOW oil pressure!

Click the image to open in full size.Diagram from grumpyvette

Last edited by SpitotRs305; 03-13-2009 at 11:39 PM.
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Old 03-17-2009, 11:58 AM   #17
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Re: Newly rebuilt engine - LOW oil pressure!

It seems the oil screen in the pan is the culprit. Because of my suspension setup the engine must be pulled in order to correct this. I'll be doing it myself, should be a ten minute fix once the engine is up in the air. Stupid little problem, but time consuming solution. Thank you for your comments, they helped shorten the diagnosis period

Last edited by Tpx; 03-17-2009 at 01:49 PM.
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Old 03-17-2009, 12:23 PM   #18
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Re: Newly rebuilt engine - LOW oil pressure!

if its your oil pump pick up you should have the builder take care of it. it should be under warranty for the labor because he must have installed it to low or he left somthing in the engine that clogged it
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Old 03-17-2009, 01:52 PM   #19
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Re: Newly rebuilt engine - LOW oil pressure!

Quote:
Originally Posted by 50bmgshooter View Post
if its your oil pump pick up you should have the builder take care of it. it should be under warranty for the labor because he must have installed it to low or he left somthing in the engine that clogged it
Yes that's the name of the part, oil pickup. It is under warranty as you said, so he'll be paying me shop wages for getting the labor done, or give him the engine to fix himself (would take days because he is very busy). So I decided to tell him I'll take it to a shop but I'm really going to do it myself. It's rated at a 4 hour job, so at 80/hour that's $320 in my pocket for fixing it myself.
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Old 03-17-2009, 02:39 PM   #20
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Re: Newly rebuilt engine - LOW oil pressure!

unless it's either a chinese or aftermarket screen, I can't see it being THAT much of a problem. When a screen falls loose entirely, the engine won't keep running. When an aftermarket screen is too close to the pan, it will hurt flow and pressure, but I've never seen it below 10 psi even when that was the case. Chinese screens have been found full of welding slag, or bent to an opening the size of a McDonalds straw, but even that is rare. Please post again once you get the pan off.
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Old 03-17-2009, 04:56 PM   #21
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Re: Newly rebuilt engine - LOW oil pressure!

sounds like a bad oil pressure sending unit, or the thing was not correctly re-installed, alot of people overlook this small item because many dont know that it exists.

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Old 03-17-2009, 06:33 PM   #22
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Re: Newly rebuilt engine - LOW oil pressure!

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sounds like a bad oil pressure sending unit, or the thing was not correctly re-installed, alot of people overlook this small item because many dont know that it exists.

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You mean a bad unit or incorrectly installed unit right
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Old 03-17-2009, 07:03 PM   #23
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Re: Newly rebuilt engine - LOW oil pressure!

If the machine shop built your engine, and now you have no oil pressure, I would deffinitely let him deal with it, I know you said he is busy, but seeing how this is his mistake, it should be at the very top of his priority list.
It probably is an internal oil leak, and the motor should be mostly disasmebled to verify everyone is there, if you were to pull the pan, replace the oil pump pickup, then reinstall it only to have the same problem, I imagine you would be pretty upset! I think that all you will have to remove is the oil pan and timing cover to check for the plugs, but maybe someone else will chime in if there is more disasembly required.

As I said, I really think the original mechanic should fix it, if you were to remove the motor and fix it, but the oil pan leaked, would he cover the time and expense to fix it, I would just take it back and tell him to make it right. That is what you paid him for in the first place right?
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Old 03-17-2009, 08:02 PM   #24
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Re: Newly rebuilt engine - LOW oil pressure!

Quote:
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You mean a bad unit or incorrectly installed unit right
yea, that would be my best guess
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Old 03-17-2009, 08:17 PM   #25
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Re: Newly rebuilt engine - LOW oil pressure!

if the OP did the coathanger test, then any misinstallation of the sender would've been found and remedied.
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Old 03-18-2009, 11:22 PM   #26
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Re: Newly rebuilt engine - LOW oil pressure!

it turns out it wasn't the pickup, plugs, or those sort of things. When I looked through it I couldn't find what was wrong. Everything was done correctly to my limited knowledge. So I took it to his shop and made him look through it. Few hours later he comes to the conclusion that there's something wrong with the oil pump? I think he said pump, and that the distributor wasn't activating the pump correctly or some such. Some line about it not reaching far enough down to make the pump work correctly. I'm no expert machanic so I don't know how these things work, but that sounds kind of fishy to me. He said he put a big block 454 pump in it and when he test ran it oil pressure was up to 30-40 and engine was running very strong. Go figure.

Does this sound right to you guys or do you think he's bull****ing me to cover his tracks?

Anyway everything's ok now and I'll be getting the engine put in tommorow and take it home hopefully the same day. He didn't charge me anything extra and even fired the guy he assigned to work on the engine. I think it's safe to say I won't be taking future engine work to him. So much for a good reputation.

Last edited by Tpx; 03-19-2009 at 12:28 AM.
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Old 03-18-2009, 11:29 PM   #27
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Re: Newly rebuilt engine - LOW oil pressure!

Sounds like he didn't put something together right and isn't fessing up to it. The question is how much invisible damage was done. You might want to cut open the oil filter or have the oil tested (they can tell if the bearings were damaged by the trace metals in the oil).

Who put the distributor in? I put one in once and the clamp slid off the base as I was tightening it, but I didn't notice. All was fine for a while until the distributor popped up and disengaged the oil pump. Luckily I had idiot lights as well as gauges and knew immediately that something was wrong.
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Old 03-19-2009, 05:45 AM   #28
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Re: Newly rebuilt engine - LOW oil pressure!

The connection between the the distributor and the oil pump is a yes/no kinda thing. It's either engaged and turning or it isn't.
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Old 03-19-2009, 06:02 AM   #29
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Re: Newly rebuilt engine - LOW oil pressure!

damon's right. You had some pressure, so it was turning.
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Old 03-19-2009, 06:02 AM
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