Appropriate 327 Idle Oil Pressure

[Carl R.]

Just a quick question fof the Corvette Gurus:

On driving my 1967 327/300 car last weekend, I noticed at idle (600rpm, H2O temp approx 190 degrees) the oil pressure reading about 10psi. I usually mix 10-30 (2)+ 10-40 (3) quarts when changing the oil. Level/color is perfect. Is this an appropriate pressure? In the summer the car runs a bit hotter in traffic. Would anyone reccomend switching to 20-50w?

(I know switching to the higher-volume oil pump would increase the #, but I don't want to peg the 45psi guage)

Thanks!

Carl

[Jerry Clark]

Re: Appropriate 327 Idle Oil Pressure

Hi Carl:

I would be very nervous with a 10psi oil pressure, do you know the condition of your engine ? Is it a rebuild candidate and is there a suspicious oil guage here ? One way or another you need to check into it, Your choice of oils and your water temperature should net more pressure if everything were correct.

jerry

[Joe L.]

Re: Appropriate 327 Idle Oil Pressure

Carl----

If your engine is running at 10 PSI oil pressure under the conditions that you describe, something is wrong. Switching to a heavier weight oil is not going to significantly improve your situation, either.

As a first step I'd check the gauge for accuracy. To do this, obtain a high quality test gauge and use it as a temporary replacement for your dash gauge. I would recommend installing a temporary oil line right from the block fitting to the test gauge. That way, you'll be able to isolate a problem to the engine or the gauge/oil pressure line system. Then, check the actual engine oil pressure under different operating conditions.

If your oil pressure proves to be accurately reflected by your gauge, you will need to go into the engine. Low oil pressure can usually be traced to worn/defective engine bearings or a defective oil pump. In the latter regard, a high volume oil pump will not improve your oil pressure, at all. A high pressure pump will. However, I don't recommend using either one. A "standard" pump, operating as designed and as part of an engine in good repair, will generate all of the oil pressure you need. Under the conditions which you described, that should be 30-40 PSI.

[Jim T.]

Re: Appropriate 327 Idle Oil Pressure

Carl are you sure the oil pressure guage in your 67 has a oil pressure guage that pegs at 45 PSI?

[Duke W.]

What's it read at 2500

Yeah, a 45 psi gage doesn't sound right. Also, what does the oil pressure read at about 2500 revs with the coolant and oil at operating temperature?

Duke

[Carl R.]

Thanks & update

Wow! Thanks for the great response!

The engine was rebuilt in 1992 about roughly 5k miles ago by a highly-reputed race engine shop in Houston. Cylinders had already been bored 0.60 over but the gentleman told me that their condition was very good & did not need rebore/sleeving. This may be due to my changing the oil far more often than necessary.

Perhaps I am mistaken that the 1967 oil gage (low-performance) pegs at 45psi - is it 60? At 2500 rpm as I remember guage reads between 30 and next (45?) hash marking. Is this OK?

I seem to remember hearing back in the 1980's that whenever folks would install the high-pressure oil pumps in the low-performance 327s that the oil guage would peg upon revving the motor.

Thanks!

Carl

[58 jeff]

Re: Appropriate 327 Idle Oil Pressure

Smoky Yunick the small block god was a beliver in 10psi per thousand rpm for race motors when cold is it higher sounds pretty loose to me but if the pressure goes up as rpm climbs you might be ok JJ

[Duke W.]

Oil pressure specs

The AMA specifications provided by Chevrolet for my '63 state that the regulator valve opens at 40-45 psi. Later in the model year the mechanical lifter engines were changed to about 60 psi and the 60 psi cluster gage was replaced with an 80 psi gage. To the best of my knowledge the base hydraulic lifter engines continued with the 40-45 psi relief spring and a 60 psi gage. My "early" '63 has a 60 psi gage with a large hash mark labeled "30" and smaller marks mid way between 0 and 30 and 30 and 60. You should be able to accurately read the gage within at least 5 psi. Ten psi sounds a little low at your idle speed, but if it is in the range of 40-45 at 2000-2500 with the oil at normal operating temperture, you are probably okay.

In the seventies GM generally reduced engine oil pressure as a way to reduce internal friction to increase fuel economy, and I recall them saying that idle oil pressure of 5 psi was okay. I was never very comfortable with this, but the fact remains that there is very little load on the bearings at idle speed. Bearing loading increases with the square of speed,so oil pressure must increase radidly above idle speed to the nominal specified value. Smokey's recommendation is for racing engines that see continuously high revs, so 40-45 psi is adequate for a moderate performance street engine.

Duke

[Joe L.]

Correction

Carl-----

My apologies. Somehow or another I missed the statement in your original post that the 10 PSI you were referring to was at IDLE. When I provided my first response it was on the basis of the 10 PSI at cruise speeds. I don't know how I got that impression; your original post was very clear. In any event, a gauge reading of 10 PSI at idle is fine. Corvette oil gauges are not that accurate, particularly at the lower end of the scale. But, even if it were accurate, 10 PSI or so at idle would be ok. Your "cruise" oil pressure reading (at about 2,500 rpm) should be in the 35-40 PSI range.

[Greg Madden]

Re: Appropriate 327 Idle Oil Pressure

I had a similar problem with my '69. I was ready to rebuild the engine, but I checked the gauge first. Good thing too, since that's what it was. Replaced the gauge & it's been fine ever since. Unfortunately, gauges are (were?) hard to find. Can any of the gauge restoration shops fix this kind of problem if the gauge is otherwise ok? And what causes this kind of problem?

Regards,

- Greg

[Stephen B.]

Re: What's it read at 2500

an industry standard is approx 10 psi per 1000rpm but certain cars have differnt pump gears and relief springs so an exact application is needed for a specific answer

[Duke W.]

Mid-year oil pressure gages

Mid-years have a direct reading oil pressure gage known as a "bourdon tube" gage. Inside the gage is a curved tube that flexes when internal pressure is applied, and the end of the tube is connected to the needle. This is a very old, simple, and generally reliable design. I suppose if it is off calibration an experienced technician could "rebend" the tube, but I don't know of anyone to recommend Perhaps there is an experienced gage repair or instrument calibration establishment could do the job. Before attempting this I would check the gage calibration with a known good test gage. If it is too far off it is probably worth checking into repairing it or procuring a good unit. The other alternative is to meerly "calibrate" the gage by recording both the dash gage and test gage reading at idle and 2500 RPM. Bourdon tube gages can be very accurate (and expensive) and are common in test setups, but the Corvette gage is likely not a precision instrument, and I would guess that design accuracy is on the order of plus or minus up to 10 percent. At some point Chevrolet switched to and electrical gage, but I don't know the year.

Duke

[Terry M.]

Re: Still real gauge in '73.....ntx

[Bill Baird]

Re: Mid-year oil pressure gages

My '75 has the electrical oil pressure gauge.

Bill Baird