Low oil pressure and rough idle

[Isaac nickerson]

Hey guys, got a k10 with 350 and 1406. I noticed today it was idling a little rough and the idle was lower at about 600 rpm. Usually it hangs out at 750. Also my oil psi was at about 8 or 9. Never seen it that low. Any ideas or initial thoughts?

 

[Isaac nickerson]

And yes I checked the oil level

 

[ali_c20]

I would check for vacuum leak first. What was your normal oil pressure at idle? Does the oil pressure go up when you rev the engine?

 

[Isaac nickerson]

Since I've had the truck it has been at 15 psi at idle and yes it does go up when I rev the engine. Once I hit 700 to 900 rpm it's back at 15psi.

 

[cstew47]

Wow, I would be extremely reluctant to drive the vehicle with those oil pressure readings. You should be at least 20 at idle and 30-40 minimum at cruising. I suspect you've got some major issues.

 

[Isaac nickerson]

What issues accompany low oil pressure? Bad oil pump?

 

[Snoots]

Mileage?

 

[Isaac nickerson]

I've driven 65 miles in the last 2 days and am still at about 3/4 of a tank.

 

[Goldie Driver]

Wow, I would be extremely reluctant to drive the vehicle with those oil pressure readings. You should be at least 20 at idle and 30-40 minimum at cruising. I suspect you've got some major issues.

While I agree, the old saw is that a SBC only needs 10 PSI per 1000 RPM or so.

I don't believe it as when the 400 in my '77 was dying, and the 350 in the '91, BOTH displayed low oil pressure at idle and down the road.

Fun fact - the '91 I decided was a science experiment and I ran Royal Purple full syn. It finally broke the crank ( !!!) when I started it one morning , but ...

I drove it to the shop under it's own power.

And, yes, it sounded like absolute ass ...

 

[Isaac nickerson]

I'm going to try changing the oil, make sure there is no gas in it, and maybe turn up the speed screw and see what happens. Any way to test a oil pressure guage?

 

[Ellie Niner]

I'm going to try changing the oil, make sure there is no gas in it, and maybe turn up the speed screw and see what happens. Any way to test a oil pressure guage?

I usually test them against a known good mechanical gauge. Depending on operating conditions, oil temperature and viscosity, oil pressure can vary quite a bit... and your pressure doesn't sound terribly low to me... though it'd be good to know more details of when you're seeing these numbers.

My butt only starts to pucker if I see much below 30 pounds hot while driving... I've seen 10 at idle on a hot day after a long drive, and it always comes right back up as soon as I come off idle.

 

[Isaac nickerson]

Thanks for the response. Out of curiosity can you rent these at auto stores? And where do you hood them up?

 

[Ellie Niner]

I imaging you can rent one... I've always just *had* an old Stewart Warner gauge with a short length of hose on it, so I've never shopped for one. The oil pressure port for the factory gauge is just to the left (driver's side) of the distributor. It you've got the stock gauge, it'll be mechanical, so there should just be a metal tube screwed into the oil pressure port, heading toward the instrument cluster through the firewall.

 

[cstew47]

While I agree, the old saw is that a SBC only needs 10 PSI per 1000 RPM or so.

I don't believe it as when the 400 in my '77 was dying, and the 350 in the '91, BOTH displayed low oil pressure at idle and down the road.

Fun fact - the '91 I decided was a science experiment and I ran Royal Purple full syn. It finally broke the crank ( !!!) when I started it one morning , but ...

I drove it to the shop under it's own power.

And, yes, it sounded like absolute ass ...

I've heard suggestions like 10bs/100 cu in. At any rate, I wouldn't drive it with the numbers he is reporting. I'm surprised it isn't make noise.

 

[cstew47]

What issues accompany low oil pressure? Bad oil pump?

Could be that or engine wear. Another possibility is a clogged oil filter.