1979 chevy 305 low oil pressure at idle!?!?!

[Boxchevrolet]

hello i swapped a used 1979 305 into my 83 k10 due to a wiped cam lobe on my 350, i have no idea how many miles are on the 305 as was given it from my brother, he bought it for 150 bucks, cold psi at idle with 15-40 is 50 psi, as the engine warms it lowers to maybe 6 psi at 1000 rpms, I'm using a mechanical oil pressure gauge, it docent knock or anything but 6 psi seems really low, I'm thinking its due to high mileage and loose bearing clearances. would it be beneficial to put in a high volume/ standard pressure oil pump to "band-aide" the loose clearances until i rebuild the 350? thanks!

[Dr_Snooz]

Sounds like a worn out engine, though possibly a defective oil relief valve as well. You could always put in some Lucas or Motor Honey or something. I'm nursing an old Honda along that way.

[Boxchevrolet]

I'm pretty sure its worn out, I've heard you can put a high volume/ standard pressure oil pump in to bring up idle pressure on a worn out motor, the oil looked like sludge when i first drained it, probably because it sat for a year or so. I'm just gonna nurse it till i build my 350

[LTZ C20]

I'm going to point out here, not to say it's fine, it might be a tired engine anyway. According to GM, a small block should be able to idle with NO mechanical problems at exactly 6 psi oil pressure. Then add 10 psi for every 1000 rpm of rotation. If the engine runs desent, doesn't knock or rattle or tick and doesn't burn oil excessivly, don't worry about. Just use a good quality detergent oil, usually a good quality regular/synthetic blend oil is good for this. Maybe a slightly thicker viscosity if you prefer to have a little more "meat" to your oil, use a quality oil filter and change your oil responsibly.

Do those things and you probably be fine.

[bd]

I'm pretty sure its worn out...the oil looked like sludge when i first drained it, probably because it sat for a year or so....

Unless you know the full history of that motor, it's more likely the oil was rarely if ever changed.  Using a high detergent multi-vis oil now may loosen all the gunk and circulate it where it doesn't belong.  It could also cause the engine to start leaking oil.  Stick with straight 30 or 40 weight oil and change it along with a new filter at 1,000 mile intervals two or three times; extend to 3,000 mi service intervals, thereafter.  And, don't drive it hard.  Once you start changing the oil and filter, the pressure may drop even further as the gunk is purged and drained.

[Boxchevrolet]

thankyall, im gonna nurse it till i build my 350, but also the 305 won't idle under 1200 rpms for some reason, the only vacuum hoses are the advance to the distrib, brake booster, and pcv, and timing is set at 8 degrees before top dead center, any ideas on why it may not idle?

[bd]

Engine RPM won't drop below 1,200 or the engine dies below 1,200 RPM? 

The stepped fast idle cam on the passenger side of the carburetor may be sticky and not allowing the throttle to close completely - wash it down thoroughly with carb spray while flicking the cam with your finger.  Also, check for vacuum leaks using the carb spray.  If those fail, disconnect the throttle cable from the carburetor to see if that makes any difference.

[philo_beddoe]

Normal idle is about 7 or 8 hundred rpm's.  According to the repair manual.


1 John 2:15-17
Jeremiah 17:7

[Boxchevrolet]

the engine dies under 1200 rpms, I've backed out the high idle screw pretty far but if i step down the idle screw to around 800 or so it'll idle really rough and eventually die, the truck is a 83 k10 with a sm46

[bd]

Does the choke plate open completely as the engine warms?  Is it puffing any smoke out the exhaust?  Any backfires through the intake or popping out the exhaust?  Have you removed and inspected the spark plugs?

Verify the firing order.  Check for vacuum leaks using Berryman's B12 or similar carburetor spray.  Check the idle mixture adjustment.

[roundhouse]

I wouldn't worry about the psi as long as it doesn't rattle or knock


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[Boxchevrolet]

chokes all the way open, I've checked timing, no backfire of any sort

[Stewart G Griffin]

1) The timing might be very retarded if it won't idle below 1200.  What does everyone think about that?


2) What weight oil are you using now?

[Irish_Alley]

sounds like a vacuum leak? but 6 psi @1000 rps?

[Boxchevrolet]

timings at 8 degrees btdc, 15-40 oil, and just dropped the pan and the pickup is stopped up near where you can't even see the screen, yet i can't get the pickup tube out it will rotate tho, should i go ahead and replace the pump as well?