Thread: Idle oil pressure

Tweet

I have a fresh 350 engine with a few performance goodies in it, Flattop's, cam, intake, and a Melling high volume oil pump. With less than 300 miles on it, I only have 10-12 pounds oil pressure at idle. Rolling down the highway the oil pressure is 45 psi. This seems kind of low for a new engine to me. Am I just paranoid or is this normal. This is my very first engine build. I've talked to the machinist that did the work and he tells me it's fine. What do you people think?

Check it with a second oil pressure gauge and sender just to be sure. Maybe someone more versed in Chevies will post to the contrary, but to me that seems a little low. I know the thinking on oil pressure has changed over the years, and we no longer want those 80 lb readings, but I like to see it never go lower than 20 lbs or I start getting nervous. Like I said, I could be wrong though.

What oil and weight are you running, and how hot does the car get?


Don

I'm running 10W50 Valvoline racing oil and my temp. gage shows 200 degrees.

I'm running 10W50 Valvoline racing oil and my temp. gage reads 200 degrees.

I'm running 10W50 Valvoline racing oil and my temp. reads 200 degrees.

Temp might be just a tad on the high side, not real bad, but just a tad. My Jeep will do the same thing, when the temp is down the pressure is good, but when the gauge starts to climb it will affect it and the pressure starts getting lower at idle.

It will be interesting to see what some of the other guys feel.


Don

OOPS! Sorry, screwed up.

////////////////////

Pat: Brings up an interesting point. How do you guys feel about multi-grade oils versus a straight weight, like 30?


Don

//////////////////////////////

The most critical time for oil flow and quick lubrication is at startup. Multi-grade is best for that. It gets more complicated to deal with the variables after that, so without a load of qualifiers tossing out preferences means only a little, so I'll leave it at that.

I know Denny is well informed enough to know how oil works, but I would like to clarify what he's saying for the sake of accuracy.............especially for those who might be prompted to do more research and might be confused by what they read elsewhere that might sound contradictory. ALL motor oils thin as they heat up, straight or multi-grade, doesn't matter. You prove this when you see your pressure reading at startup being a higher number than when the engine gets to operating temp (assuming you're reading at the same rpm). Pressure values are a measure of resistance to flow. The more viscous the the oil, the higher the resistance to flow, the higher the pressure reading. That's why most oil pressure questions that don't include noting the oil's viscosity aren't able to be addressed accurately.

To save me a lot of typing (keyboarding I guess would be more accurate) here's a decent article that explains what's at work for those that like more research; http://www.texacoxpresslube.com/carc...viscosity.html

But just to put a short, inconcise summary on it, oil vis is graded basically at two temperatures for a straight grade. 100f, and 210f (the article above is at 40c and 100c, essentially the same). If the oil flows through the test device at a certain, measured time standard it is graded accordingly. For example the same quantity of an SAE 20 will take longer, at the same temp, than an SAE10 to flow through the test device. Each successive higher grade does likewise.

Multigrades, designated by having two grading numbers, the first followed by a w (for winter, not weight as some mistakenly believe) measured at essentially 0 degrees f (actually done in a cold cranking simulator as referenced in the article), and the second being the rate of flow at 210f. So, for instance, a 10w40 oil has the characteristics of a straight grade 10 at 0 degrees, and the flow characteristics of a 40 at 210f. The idea being to give the quicker flow of the 10w at startup, and the "thicker" (in quotes because it's still thinner at the high temp than at low temp, but not as thin as a straight 10 would be) protection of the 40 at operating temp.

Yeah, its been a common fallacy that multigrade gets thicker as the temp goes up. It just maintains the same viscosity through the temp range.
If it's 20 - 50, it'll be the same as 20W would be cold and the same as 50W would be when hot.

If that low pressure at idle really bugs you, an old trick to kick up your oil pressure is to put a small shim or washer (about 1/16") behind the bypass checkball spring in the oil pump.

Be carful not to make it too thick...the first time I tried it I tried one about 1/4" and broke my oil pressure gage at 80 lbs when I fired it up.

////////////////////

//////////////////////////