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Discussion Starter #1
My mid-80’s 305 in my 1980 is showing oil pressure around middle 20’s when warm idling, increasing To 40-50 when revving in neutral. As it’s not roadworthy (just purchased to restore) I don’t know about while driving. Fresh oil change today with no change. Oil level is good, no apparent leaks.

A neighbor with a ‘79 also with a 305 said that was way low and I should be around 40. Called my father in law who knows his way around a mother better than I do and he also said it should be 38-40.

Searched it and see some contradictory info. Is this something I need to address?

I also have a very faint choke light lit up on the dash. Just noticed that tonight after dark, too dim to see in daylight. Search said there could be a connection.

What should my plan of action be? I’d like to avoid dropping the pan if at all possible but not at the expense of doing damage. Anything I can rule out before replacing the oil pump!
 

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seen many post saying people have oil pressure in the tens & it's fine for a Chevy as long it goes up with the throttle
They say 10 psi per thousand RPM's, something like that
I would get worried when the pressure doesn't go up with the throttle
The engine guys should chime in soon
 

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how much pressure you have, depends on the oil weight too..

the manual has allways said 30-40 psi at hot idle for a SBC..
that's for a bone-stock grocery getter..

if your measuring 10-20 psi pressure at the discharge of the pump,,
what would the pressure be at the front of the motor,
where the #1 main and rod bearings get oiled last??

I was allways told 10psi for each 1000rpm too,
but that's a over- simplification with out the rest of the saying..
that applies to a Hi-RPM situation,
50psi at 5000rpm
60psi at 6000rpm
70psi at 7000rpm
 

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Discussion Starter #4
I’m starting to think it may be a gauge issue. I moved some wires around to get to the casting number and now the gauge reads 0. Think I bumped something. That got me to follow the wires from the gauge and the clear tube that goes to the oil pressure sender looks pretty rough and has a couple small kinks. I’ll replace that and see if it resolves it before digging any deeper into this issue
 

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I’m starting to think it may be a gauge issue. I moved some wires around to get to the casting number and now the gauge reads 0. Think I bumped something. That got me to follow the wires from the gauge and the clear tube that goes to the oil pressure sender looks pretty rough and has a couple small kinks. I’ll replace that and see if it resolves it before digging any deeper into this issue
Do your self a favor and buy the cooper line kit. I learned the hard way
 

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Don't forget to bleed the line, seen far too many oil tubes that had a few spurts of oil in them and a ton of air bubbles. Air compresses, oil doesn't, so an unbled line can give you false readings at the guage.
 

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Discussion Starter #8
Don't forget to bleed the line, seen far too many oil tubes that had a few spurts of oil in them and a ton of air bubbles. Air compresses, oil doesn't, so an unbled line can give you false readings at the guage.
Hmm, this may be the problem. I noticed when I took the old line out it was mostly air with some oil here and there. How do you bleed the line?
 

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My mid-80’s 305 in my 1980 is showing oil pressure around middle 20’s when warm idling, increasing To 40-50 when revving in neutral. As it’s not roadworthy (just purchased to restore) I don’t know about while driving. Fresh oil change today with no change. Oil level is good, no apparent leaks.

A neighbor with a ‘79 also with a 305 said that was way low and I should be around 40. Called my father in law who knows his way around a mother better than I do and he also said it should be 38-40.

Searched it and see some contradictory info. Is this something I need to address?

I also have a very faint choke light lit up on the dash. Just noticed that tonight after dark, too dim to see in daylight. Search said there could be a connection.

What should my plan of action be? I’d like to avoid dropping the pan if at all possible but not at the expense of doing damage. Anything I can rule out before replacing the oil pump!
Man, that thing will run forever like that, so long as it doesn't decrease over time, it'll be fine. As long as it increases with rpm, and stays above 10 psi at idle, it'll be fine. Of corse take it easy on the old thing. Those old engines could probably survive with 6psi at idle, but you'd have to really baby it then. Gotta love those old chevy engines.
 

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To bleed the line you will need the oil pressure to push the air out.
Disable the ignition
Loosen the line at the gauge
put the line into something to catch the oil.
Crank the engine until a steady flow of oil. It won't take but a few seconds.
 

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Lil bit of air doesn't hurt lol, it's when you have a line full of air you get bad readings at lower pressures as the air compresses. Not hard to really have 20psi but guage reads 10 ish. Especially true if there's a kink or tight coils as that just adds resistance. Anyway, there isn't air on the guage, theres a spring loaded plunger on the end of the tube, force moves the plunger which pushes the needle, spring pulls the plunger back.
 

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Discussion Starter #15
Well, I believe this issue is resolved. Don’t want to speak too soon since all testing is with the car in park (it’s not roadworthy yet) but I got the new gauge installed and am now seeing pressure on the middle 30’s at hot idle, with appropriate increases when revving it. I bled the line with the method as described by 464elky. Looks like my oil pump is ok. Now on to the water pump!
 

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As far as the choke light goes, first clean the connector where the plug in the dash mates to your instrument cluster. Then check the instrument ground. Might be some ground resistance/feedback.
Oil pressure sound OK to me.
 

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Discussion Starter #18
I’ve followed the choke wire to a connector that goes into a harness and disappears near the heater core. I don’t believe the oil pressure switch exists anymore. This car has been rewired, and a real half a$$ job of it. I haven’t had time to mess with it the past couple days and probably won’t till mid next week, but sorting out wiring is high on my list.
 

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Sounds like you need to get everything straight, then worry about what works and what doesn't, or you'll be chasing ghosts for days. Good luck.
 
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