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Old 01-30-2012, 07:35 PM
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Low Oil Pressure

I have a new 355ci motor with new bearings cam shaft lifters etc and had built. When cold it has 45-55 psi at idle. Once it warms up the idle pressure is about 5-10 at a stop light. It was not that low initially, now that it has about 150 miles on it it scares meit is so low. Looking for ideas or is it time to pull the motor out and have a new mechanic / engine builder look at it.

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Old 01-30-2012, 10:12 PM
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what weight oil and brand are you running?
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Old 01-31-2012, 06:52 AM
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Low oil pressure

I am using valvoline VR-1 20-50
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Old 01-31-2012, 07:40 AM
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Replace the distributor itself.
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Old 01-31-2012, 09:14 AM
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Quote:
Originally Posted by Joer5000
I have a new 355ci motor with new bearings cam shaft lifters etc and had built. When cold it has 45-55 psi at idle. Once it warms up the idle pressure is about 5-10 at a stop light. It was not that low initially, now that it has about 150 miles on it it scares meit is so low. Looking for ideas or is it time to pull the motor out and have a new mechanic / engine builder look at it.
Well which is 5 or 10? Check it with a known accurate mechanical gauge in the port behind the intake manifold
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Old 01-31-2012, 11:02 AM
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Hi,im running vr1 20/50 in my fresh sbc,I had low oil pressure about 10lbs at hot idle,changed my gauge to a good mechanical one,reads 18lbs at idle,worth a try?

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Old 01-31-2012, 11:33 AM
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I had 10psi of oil pressure hot with 20W-50 oil, after rebuilding my motor, and when I got a new distributor for my 406sbc the oil pressure jump to 30psi hot at idle, 60-65 psi at cruise 85 psi when I first cranked to 406 to a cold idle. This is a standard chevy high pressure oil pump. That is just replacing the distributor.
With the oil primer and hand drill you should read at least 70psi. on the gauge. If not you got other problem. And guess what, I'm using a FRAM oil filter HP-4

Last edited by lg1969; 01-31-2012 at 11:57 AM.
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Old 01-31-2012, 07:52 PM
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low oil pressure

My distributor is brand new and why would that affect oil pressure, also the idle pressure varies. I should get the car back from the tranny shop friday night as i was sold a bad transmission from a guy named Bill Butterfield in Tempe AZ and he sold me the bad motor and transmission so i got screwed double time!! My bad i trusted a end user and should have bought it from a business like summit lesson learned
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Old 02-01-2012, 10:44 AM
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Quote:
Originally Posted by Joer5000
My distributor is brand new and why would that affect oil pressure?
I would be interested in the explanation of this as well.
Is it just the oil pump drive shaft may be worn or something?
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Old 02-01-2012, 12:02 PM
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Look at this post and read cobalt327 statement.
This happen to me twice. One was a rebuilt dist. from Auto parts store. The other was an Accel dual point dist.
Low oil pressure on SBC

Last edited by lg1969; 02-01-2012 at 12:17 PM.
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Old 02-01-2012, 12:13 PM
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Thank's man,
That now makes perfect sense, it's a Chevy thing
Pontiac do it different
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Old 02-01-2012, 01:32 PM
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Quote:
Originally Posted by Joer5000
I have a new 355ci motor with new bearings cam shaft lifters etc and had built. When cold it has 45-55 psi at idle. Once it warms up the idle pressure is about 5-10 at a stop light. It was not that low initially, now that it has about 150 miles on it it scares meit is so low. Looking for ideas or is it time to pull the motor out and have a new mechanic / engine builder look at it.
For 20-50 oil this is low both hot and cold. When cold an idling, the pump should be able to pop the bypass valve with this weight oil, that is usually somewhere in the range of 45-65 psi for a stock SBC pump. Idle hot should be 20-30 and cruise say about 2500 RPM should be just off the bypass at about 50-55 psi. A heavier oil will show more pressure up to the bypass opening. A lighter weight will show less but not abnormally less. I'd be REALLY concerned about 5-10 hot idle that's getting down in the range where the double knock of a failed rod bearing ain't far away.

Reasons:

- Since there has been talk about the distributor fit lets start there, a distributor that is not positioned correctly can shut off oil flow to the right side lifter galley, or open a leak which would reduce pressure uniformly but probably not more than 10 PSI because this galley's feed passage is not too big. Always a good idea when assembling an SBC to leave out the right side rear galley plug till a test fit with intake in place is made of the distributor as you can see whether the pass groove aligns with the galley. Just remember to put the plug back in when done with this inspection, otherwise there will be a pressure leak out of the engine behind the flywheel, not much fun to fix at that point. Changing back to distributor position; if the distributor doesn't sit properly to close off the top and bottom of the passage the leak is internal to the engine, so this will leave no visible mark as to where the oil is going cause it's going back to the pan. Leakage because of this isn't a common problem because the bosses on either side of the passage are quite thick so it takes a lot of miss-alignment to put them where a leak develops, the common thing is the passage gets blocked which will show up as lifter noise.

- Another common leak is air into the inlet, this happens because the pickup is too high from the bottom of the sump. This is often a problem when using a deep sump pan as many makers supply a stock length pickup that has to be bent to fit the deeper pan. The pickup should be 1/4 to 3/8s off the pan. It is increasingly common, when going with a 7 quart pan for example, to find the pick up 3/4's of an inch from the pan bottom. If this happens a vortex forms which adds air to the ingoing oil. As a builder these days you've got to check and recheck everything as most parts a foreign made and just don't fit correctly.

- Another common problem with the pickup is air leakage where it's pressed into the pump housing. Often this happens when trying to adjust it for pan depth, the other thing is cracking the pickup tube when doing this.

- The other end of the pickup issues is getting it too close to the bottom to where oil can't flow in as fast as it's being pumped.

- The other cause is excess bearing clearance, this can be cam and/or crank bearings to where the loss rate through the bearings is higher than pump output.

- There can be drain-back issues from the top end, this is rare but it happens.

- Excess windage, this happens mostly with high volume pumps and no windage tray. This gets into oil being trapped around the crank to where the pump isn't getting fed well enough. This often happens along with excessive pickup to pan clearance. This is usually a high RPM problem as well not an idle problem.

- Sometimes it's the pump from loose shafting or gears, damage from ingestion of foreign material to the gears and/or housing. Another common problem is a burr in the bypass drilling that catches the valve holding it partially open all the time. This can be the cross drilling plug as well. Or if the pick up was welded to the pump housing with the bypass spring installed, the spring is heat damaged and open the valve too early.

- Last I guess is the gauge or sender isn't working correctly. While last it's something to look at first as it's usually easier to get at than these other things.

Lots of possibilities to check on. Good Luck!

Bogie
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Old 02-01-2012, 07:31 PM
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Low Oil Pressure

Oldbogle that is a lot to absorb! first the 350 block is 30 over. everything is brand new including the high volume oil pump. I was there when it was assembled until 5am (long story??) rather not get into why other than i wasn't leaving without my motor! Their was no windage tray, he did torque the oil pump down. we measured the oil pump pickup to the pan bottom which was about 1/4 inch. The pickup was put in with vice grips and a hammer?? The rods and mains were torqued, The low pressure occurs at idle when the motor was warmed up,, cold it was about 40 psi. When i dropped it off at the tranny shop 3 weeks ago i had to drive it in 2nd gear at 40 mph and at light it was showing 5-10 psi and that had me concerned. When i get it friday night i will take it on the freeway to get home and see what it looks like. I am mot a hard core motor-head although i know the basics, at 20 years old i used to assemble my 427 with dual 660 holleys in my 67 GTO but that was about 35 years ago! I am dyeing for a 5 speed but with having to buy a new motor and trans the 5 speed will have to wait a while. Anyway i will have to have a professional look the motor over before i attempt any kind of high RPM burn out or hard run on the motor!
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Old 02-01-2012, 07:42 PM
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Just for laugh and giggle try to find another distributor and see what happen to the oil pressure if everything else failed.
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