wierd readings

1

1hc72

Member
Ok here we go, I am having some strange reading on oil pressure, I have 2 gauges,1 is factory and 1 is aftermarket. The aftermarket at idle drops tp 0 then when I hit the gas it goes to 40 psi. The oem gauge stays about in the middle whilwe driving or at an idle.


What doea this mean?
 
The mechanical gauge is behaving fairly normally. How is the gauge indexed? What I mean is, does it have marks for every 10 psi or every 5 psi, or every 1 psi? At hot idle, 7psi while low by big 3 standards is sufficient for an sv engine. Are you sure your gauge is truly at zero? Maybe it looks close to zero, but due to the indexing it is actually just a smidge above? If it was truly zero psi at idle, I would think your valve train would soon confirm it with plenty of lifter rattle. As to the factory gauge, inaccurate readings are the norm rather than the exception after so many years of service. Does the needle react at all to changes in engine speed? I would trust your mechanical gauge well ahead of the stocker.
 
For definitive oil pressure data, the gauge being used must be a very high resolution version, just as trev advises. Many of the inexpensive aftermarket gauges are actually worse than any oem gauge setup which is only a "tell-tale" and is not a definitive oil pressure gauge.

I've conducted quite a few tests of various pickall and Scout II oem oil pressure indicators using new senders so I know what the various needle positions of the oem gauge set actually indicates. Your description tells me that your oem gauge system is not functioning correctly.

In my own vehicles, I run the oem gauge system in parallel with an aftermarket gauge...and both of those have been validated with a high-end "shop"-type oil pressure gauge.

Specified oil pressure range in all sv engines is:

oil viscosity-30wt., oil temperature 200*f.
10-20psi at curb idle speed
40-50psi at 1800rpm

exact same oil pressure specs are valid for the I-4 engine series.

Do not ever think of the engine lubrication system on these motors (either sv or I-4) as anything similar inna chryfordrolet engine, the only thing they have in common is oil. These engines are high volume/medium pressure lubrication systems.

When the lifter galleries "starve" for oil, lifter rattle becomes immediate.

If you are gonna play with these motors, you need to become intimately familiar with the lubrication schematic.
 
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Here's my two-cents worth......

I agree with michael about the oil gauges you have, and further agree that if your oil pressure was "0" as stated, you would have a heckuva clatter going on in the lifter/valve-train area.

Here's a little "101" on what oil pressure is:

viscosity is the oil's resistance to flow, so the higher viscosity, the higher the oil pressure would be.

At start up with a cold engine, your oil pressure should be the highest it reads on the gauge, then as the engine gradually warms up, it will drop down into what would be the "normal range" which michael referred to. The reason for that is because regular engine oils have the tendency to get thicker when they are cold, and this is why the oil pressure is higher when cold than when hot. The better oils, such as swepco, will not thicken excessively when cold, nor thin excessively when hot, but there should still be a difference in the oil pressure gauge between the cold and hot engine times.

After the engine is warmed up to normal operating temperature, there should be a definite difference between the idle oil pressure and the higher rpm pressure, the oil pressure gauge should'nt just give you one steady reading.

Dick floryanowich
swepco
 
Ill upload a pic of the after market gauge and a more acccurate reading over the next couple of days
 
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