Oil Pressure Woes !!

Rjaaaaaa

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Jul 11, 2016
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When the engine gets up to temp. the oil pressure decreases ? When I go to idle the oil pressure needle drops off completely, it comes back up when I pick up the rpms. This is the factory gauge with new sending unit. When I first start and run it the pressure reads about mid scale on factory gauge and only drops a little at idle.
I temporally connected a line pressure gauge and it reads 15-18 at idle when hot but at 4k it only goes up to 28-30#. Engine sounds ok, no unusual sounds from valve train at idle
What do you think? Are these ok ? What should it read Need new oil pump?
With line pressure gauge it never drops to zero.
 
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MFE92

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The factory gauge drops to nothing below about 12 lbs. 15-18 at idle is technically enough, but a healthy windsor 5.0 should be showing way more than that IMO. What happens when you apply load?
 

Rjaaaaaa

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The factory gauge drops to nothing below about 12 lbs. 15-18 at idle is technically enough, but a healthy windsor 5.0 should be showing way more than that IMO. What happens when you apply load?
Yea I figured the sending unit had a threshold but it sure makes me edgey when I see the oil pressure gauge go to zero.
The pressure picks up as soon as the rpms pick up.
 

stykthyn

I want to measure mine. It doesn't look that tall.
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I would invest in a cheap mechanical gauge just to make sure you actually have decent pressure. I've had a 20 dollar sunpro in my jeep for several years now since the stock unit failed. I run autometer in the fox, but just for diagnostics a simple unit will do for now.
 

Rjaaaaaa

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How many miles and are the engine temps normal?
Not sure on the miles, I was told by PO that it was pretty fresh rebuild. From what I can see with new looking gaskets it seems believable. The engine temps. are normal with a fresh 180 thermostat. but the problems is only when the engine is up to operating temp.
Took car out today (near 70 outside here) pressure held good for 30 min. ride the went south. ???
oil pressure comes up to center position on factory gauge which looks like 45 - 50# but is really only 30#
 

Rjaaaaaa

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I would invest in a cheap mechanical gauge just to make sure you actually have decent pressure. I've had a 20 dollar sunpro in my jeep for several years now since the stock unit failed. I run autometer in the fox, but just for diagnostics a simple unit will do for now.
I borrowed a sunpro mech. gauge and hooked it in temp. That's what was reading 18-20# at idle and 30# at 4k.
 

stykthyn

I want to measure mine. It doesn't look that tall.
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The 18-20 at hot idle is "OK" the 30 at 4k seems low to me. If you aren't racing and this is just a pleasuremobile that engine could last for years. I'd bet my paycheck that bottom end is untouched. Top end was gone through for a bad gasket or to get the heads rebuilt and then put back together.
 

Rjaaaaaa

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The factory gauge drops to nothing below about 12 lbs. 15-18 at idle is technically enough, but a healthy windsor 5.0 should be showing way more than that IMO. What happens when you apply load?
This engine is a 306 with x cam, head work, edelbrock intake, bbk tb, maf & fuel rails. The engine runs strong and I never hear anything unusual from the engine. It also has the reduced diameter pulley setup which seems to have a bad effect on the alt. at low rpm / idle, I was thinking this may figure into gauge output problem ???
 

stykthyn

I want to measure mine. It doesn't look that tall.
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If you are testing with a mechanical gauge you can eliminate any voltage issues. If the x Cam has a large amount of lope your idle numbers could be a tad off but even at its lowest point your numbers sound low.
 

General karthief

wonder how much it would cost to ship you a pair
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What oil are you running?
Not that that is the problem but you can buy yourself some time with a different viscosity oil, and never, never, ever use a fram oil filter, speaking of, yank that filter off and cut it open and see what you find in there, you could also have your oil tested for metal contaminants,
 
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stykthyn

I want to measure mine. It doesn't look that tall.
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What oil are you running?
Not that that is the problem but you can buy yourself some time with a different viscosity oil, and never, never, ever use a fram oil filter, speaking of, yank that filter off and cut it open and see what you find in there, you could also have your oil tested for metal contaminants,
I didn't want to go there as its a band aid, but you are correct. Heavier oil could bump his numbers. The only other thing I can think of assuming this is a fresh build is that the gasket wasn't applied to the pump and the pick up allowing pressure to escape or that the oil pick up itself isn't in a good position.
 
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Rjaaaaaa

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Agreed. At the very least dump the oil and run it through a paper strainer and look for the shiny.
Ugh, didn't want to go there !! But I did give it some thought. Oil pan had been off, I see fresh rtv. I just had this engine out and sitting on the floor for 2 months, could have taken care of any problem then:bang: but everything seemed ok before I pulled it.
yanking it out is not a problem but only if necessary.
I'll do the oil filter and see.
 

stykthyn

I want to measure mine. It doesn't look that tall.
10 Year Member
Jul 6, 2006
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Ugh, didn't want to go there !! But I did give it some thought. Oil pan had been off, I see fresh rtv. I just had this engine out and sitting on the floor for 2 months, could have taken care of any problem then:bang: but everything seemed ok before I pulled it.
yanking it out is not a problem but only if necessary.
I'll do the oil filter and see.
Will this isn't really an issue that could have been diagnosed easily with the engine out of the car. If you don't have a significant amount of metal( break in will produce some) then it's time to examine your pump/pick up. While you have the engine out doing that it's a no brainer to pop the main caps and check your bearings.
 

MFE92

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Yea I figured the sending unit had a threshold but it sure makes me edgey when I see the oil pressure gauge go to zero.
The pressure picks up as soon as the rpms pick up.
Say you're cruising along at 2500 RPM in 3rd and floor it, does the pressure rise/hold steady, or drop?
 

MFE92

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Then it's likely not a split block, but it sounds like the bearings were either set up REALLY loose, or have worn that way. I would run a http://www.blackstone-labs.com/ or other lab analysis on it, if you're near a big city there's probably somebody local. Look for high lead and copper levels.
 
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Rjaaaaaa

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Ok, so I did an engine flush today and changed the oil and filter.
I didn't see any of the tell tale signs of metal or copper material mixer in the oil. Nothing shiny or metallic swirling in the oil when held out in sun light.
I even dipped a magnet into the oil with very little of anything on it.
I opened up the filter with a knife so I didn't make any metal flakes and found a few sparkles down in the pleats but I think you will probably see this in any engine ?:thinking:
I put in some 10w40 oil and added a quart of STP like stuff just to see what will happen, warmed it up and took it out for a drive :burnout:, pressure on dash gauge was normal but took a nose dive while sitting at a light at idle. Just a little throttle and it picked right up ??
I ordered a new sending unit to see if that might be some of the problem or just to rule it out.
I'm not going to pull it apart yet, I'll run it a while and do the oil again and see.
Nice weather here for awhile so I'm going to work on the hood and cowling.
 
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