Oil Pressure upgrade

[Schurkey]

I put a standard Melling replacement in my motor. My factory gauge reads 60psi at idle.

HOT idle, automatic in gear? Either your oil is WAY too thick...or the gauge is wildly inaccurate.

My guess is the latter.

The sending unit I described above is known as a high-failure item; when (not if) it fails, it can read too high...or too low...or wildly variable. Sometimes when you unscrew them from the adapter, they're so full of oil that they slosh.

But maybe your engine takes a different sender.

My K1500 shows a pegged oil pressure gauge at idle in gear, cold. By the time the engine is warmed-up, I'm at 12--15 psi. 5W-30 Amsoil XL. But normal driving is typically 40+ psi. I'm not worried about it, even if I expected better pressure at idle.

But isn't oil pressure a function of bearing clearances?

That, and all the other sources of internal oil leakage (intentional, and unintentional.)

The valvetrain is bleeding oil (and therefore oil pressure) at the rocker arms.

The block bleeds oil at each lifter bore, some of that oil lubes the cam lobes.

Chevies bleed oil where the distributor pushes into the lower part of the block, just above the cam. Some of that oil lubes the cam and distributor gears.

Many engines have vented plugs at the far end of oil galleries, to purge air at startup. Many folks think the air-purging vents are intended to lubricate the timing chain. Once the air is gone...they're spitting oil.

More and more engines are using oil jets to squirt the underside of the piston, to keep the piston head cool.

So, yes, cam, main, and rod bearing clearance can affect oil pressure, but so do the other three- or four-dozen internal oil leaks.

Isn't a high pressure pump for an engine with tighter clearances? But for a given bearing clearance and RPM, increasing the fluid flow will obviously also increase the oil pressure...if I recall correctly from basic fluid mechanics theory.

More a matter of high RPM than tight clearance, although the two are inversely related.

High RPM typically requires looser bearing clearance. Thus high-volume oil pumps to supply a greater amount of oil across the bearing to carry-away heat, while still maintaining enough pressure to force oil into the rod bearings.

'Course, for drag racing, folks have been cutting down oil pump capacity and using thinner oil so less energy is "wasted" pumping oil, and more can be used to push the car down the track. I don't know where the state-of-the-art is with NAPCAR and other long-distance racing; although I'd easily believe they're all going to "thin" oil and minimal oil pumps.

 

[thinger2]

Yep. the factory oil pressure gauge and the oil pressure switches vary wildly even when new.
I think ive mentioned before that I got a smoking deal on a bunch of nos chevy parts awhile back.
Just for ***** and giggles and an excuse to drink beer in the shop, Ive tried 4 or 5 brand new mostly gm switches and gotten very different results.
Anywhere from a check gauges light to 80 pounds at hot idle and one that just flips back and forth.
They cant be trusted at all.
The factory gauge is more of an indication that something is happening, maybe kinda sorta could be.
After checking it with two different mechanical gauges I actually have 60 at cold start and 25 ish at hot idle.
With 240k on it Im just fine with those readings.
When it gets to an actual 10 at hot idle then ill start thinking about yanking it.
I figure that gives me a few more years to figure out how to stick this built fresh Olds 350 into a K2500 and make it work with a 4l60e.
Should be easy right? I dont foresee any problems.
I should also probably fix the garage heater first
Its getting kinda hazy in here.
Thinking about opening a window and rethinking that idea.

 

[L31MaxExpress]

Yep. the factory oil pressure gauge and the oil pressure switches vary wildly even when new.
I think ive mentioned before that I got a smoking deal on a bunch of nos chevy parts awhile back.
Just for ***** and giggles and an excuse to drink beer in the shop, Ive tried 4 or 5 brand new mostly gm switches and gotten very different results.
Anywhere from a check gauges light to 80 pounds at hot idle and one that just flips back and forth.
They cant be trusted at all.
The factory gauge is more of an indication that something is happening, maybe kinda sorta could be.
After checking it with two different mechanical gauges I actually have 60 at cold start and 25 ish at hot idle.
With 240k on it Im just fine with those readings.
When it gets to an actual 10 at hot idle then ill start thinking about yanking it.
I figure that gives me a few more years to figure out how to stick this built fresh Olds 350 into a K2500 and make it work with a 4l60e.
Should be easy right? I dont foresee any problems.
I should also probably fix the garage heater first
Its getting kinda hazy in here.
Thinking about opening a window and rethinking that idea.

My oil pressure gauge in the G20, Express van and the Tahoe are all fairly accurate compared to a mechanical gauge. Its the temperature gauge that is nuts. The cluster reading in the cylinder head can vary as much as 40°F from what the PCM sees in the water crossover in the intake manifold. The fuel gauge on the Express van is also no longer accurate after a new Delphi pump went into it. It reads empty with a solid 8 gallons of fuel left. Atleast it doesn't swing to full in the last 1/4 tank like the OEM sending unit did.

 

[thinger2]

My oil pressure gauge in the G20, Express van and the Tahoe are all fairly accurate compared to a mechanical gauge. Its the temperature gauge that is nuts. The cluster reading in the cylinder head can vary as much as 40°F from what the PCM sees in the water crossover in the intake manifold. The fuel gauge on the Express van is also no longer accurate after a new Delphi pump went into it. It reads empty with a solid 8 gallons of fuel left. Atleast it doesn't swing to full in the last 1/4 tank like the OEM sending unit did.

For sure check out the grounds.
The manifold grounds and the head to firewall to frame grounds.
It can solve a lot of gauge problems and worth the effort

 

[L31MaxExpress]

For sure check out the grounds.
The manifold grounds and the head to firewall to frame grounds.
It can solve a lot of gauge problems and worth the effort

Checked and cleaned them with the engine swaps. Also replaced the ground straps with new ones. Temp sending unit reading is wrong because its more reading the temperature of the cylinder head than the coolant.

 

[thinger2]

Checked and cleaned them with the engine swaps. Also replaced the ground straps with new ones. Temp sending unit reading is wrong because its more reading the temperature of the cylinder head than the coolant.

You have 2 temp sensors.
one in the manifold that provides feed to the ecm and one in the head that feeds the gauge.