TerryR

Hope this is an easy question.

I have a engine that gets fed with a 1/4" oil line (this line is after the oil pump). With this 1/4" oil line it has an overall oil pressure of 10lbs at idle and 50lbs at 4000rpm. If I switched out the oil line with a 5/32 line and it still developed the same 10lbs of oil pressure at idle and 50lbs at 4000rpm would this mean the 5/32" line is equivalent to the 1/4" line for this application. I know the smaller 5/32" line can't flow the same as the larger 1/4" line but since they are developing the same pressure at the same RPM could this mean the oil line is NOT a restriction in the system, is it something internal in the engine after the oil line? Any help or thoughts are appreciated. Thanks Terry


Updated with to more specific information:

I'm thoroughly confused as I've increased the line size and oil pressure still remains the same! Please let me know if the following data makes or changes anyones thougths.

Stock oil line that is being substituted is 1/4" inner diameter. What's before or after this external line I can't cant see/know.

I've swapped the 1/4" line with a 5/32 line and a 3/8" line.

Testing has showed the oil pressure to remain constant between the lines even when I switch out to a smaller or larger line. Roughly 10lb at idle(950rpm) and 50lbs at 4000rpm. Those reading are with the engine at working temp. Pressure was up to 32lbs at idle when cold but this remains true of all lines again. They all registered the same.

Although I know it's not recommended (do to the engine not getting oil) I did disconnect the line and measured the amount of fluid the pump puts out in 30 seconds with both the larger 3/8" line and the smaller 5/32" line. It was roughly 48 ounces at idle for both lines. I didn't write down PSI during the test but I think I remember the 3/8" line measuring roughly 2lbs of pressure while the 5/32" line was roughly 6lbs.

I'm not sure if this info is needed but if it makes any difference the pressure release valve is roughly 65-75psi. This valve keeps pressure from building too high by returning the high pressure fluid back into the oil pan and it's located before the oil lines in question.

What would you hypothesize from the above tests? Do you think a 5/32" line is adequate for the system?

Any thoughts or comments are welcome and needed. If some important piece of data is missing please let me know and I'm happy to get it. Thanks Terry


[Modified by TerryR, 10:28 PM 7/27/2003]


[Modified by TerryR, 10:29 PM 7/27/2003]

rgregory

If you put on a smaller line and have the same pressure then you are flowing less volume. So say if your pump only has the ability to make 10psi and you drop to a smaller line you are cutting your flow. The smaller the line the more frictional losses and thus higher pressure and higher flow rate is needed to flow the same volume.

So in regards to what you are asking if the pressure stays the same something upstream is requlating the pressure.

Chris@SD

If you are not having glitches where the oil pressure drops and spikes, you are not starving your oil pump. Too small of a feed line is going to starve the oil pump. Oil pressure is set by your bearing clearances.

Good Luck,

TerryR

Thnaks guys, this is after the pressure after the oil pump. I was thinking that the oil pressure would somewhat be dictated by the bearing clearances.

I understand that to get the same amount of volume in a line pressure must increase. But if the pressure is being dictated by the bearing clearances how does this reflect to my question, do you think I'm not flowing the same amount using the smaller line if pressure remains the same? Thanks Terry

Bill Dearborn

Think of it in electrical terms. If you had a voltage supply (oil pressure) that you could vary from 10 to 40 volts and applied it across a resistor (1/4 inch line) you would get a certain current flow (oil flow) for each voltage setting. Increasing the value of the resistor (decreasing the size of the line) will give you less current (less oil flow) unless you increase the voltage (pressure). Its known as Ohm's law (Volts = Current times Resistance) and is an exact analog to fluid flow. Another thing to remember, the flow is limited by the smallest diameter in the system no matter how big the rest of the system is.

Bill

TerryR

I'm thoroughly confused as I've just increased the line size and oil pressure still remains the same! Please let me know if the following data makes or changes anyones thougths.

Stock oil line that is being substituted is 1/4" inner diameter. What's before or after this external line I can't cant see/know.

I've swapped the 1/4" line with a 5/32 line and a 3/8" line.

Testing has showed the oil pressure to remain constant between the lines even when I switch out to a smaller or larger line. Roughly 10lb at idle(950rpm) and 50lbs at 4000rpm. Those reading are with the engine at working temp. Pressure was up to 32lbs at idle when cold but this remains true of all lines again. They all registered the same.

Although I know it's not recommended (do to the engine not getting oil) I did disconnect the line and measured the amount of fluid the pump puts out in 30 seconds with both the larger 3/8" line and the smaller 5/32" line. It was roughly 48 ounces at idle for both lines. I didn't write down PSI during the test but I think I remember the 3/8" line measuring roughly 2lbs of pressure while the 5/32" line was roughly 6lbs.

I'm not sure if this info is needed but if it makes any difference the pressure release valve is roughly 65-75psi. This valve keeps pressure from building too high by returning the high pressure fluid back into the oil pan and it's located before the oil lines in question.

What would you hypothesize from the above tests? Do you think a 5/32" line is adequate for the system?

Any thoughts or comments are welcome and needed. If some important piece of data is missing please let me know and I'm happy to get it. Thanks Terry





[Modified by TerryR, 10:28 PM 7/27/2003]

Chris@SD

What you are trying to find out is whether the line can give you enough volume. I would not worry so much about idle or 4000 RPM but more along the lines of 7000 RPM or whatever the redline will be. In this case, too much is better than too little. There has got to be a reason you want to go with a smaller line, but why, I do not know....

TerryR

Chris, the engine is capable of 6500RPM which actually puts the pressure into the pressure release valve territory of about 65-80lbs where it starts to recirculate the oil from back to the oil pan to release the extra pressure. The reason for my concern is I've purchased a kit that uses the smaller lines. I don't think the homework was done and want to prevent long term engine wear.

I know a larger line has the capability to flow more but what confuses me is all three lines read the same on the pressure gauge. Does this mean the oil flow is being met by all three lines? Maybe the bearing clearances are limiting the overall flow to a certain amount? Thanks Terry

Iggy Pop

GM says anything 9 lbs. or above at idle is normal.I find this true but nerve racking all the same.My cars a 427 TT and the hotter the oil gets 220+ the lower the O.pres. drops never went below 11-12.
To set my mind at ease I use Red Line 10-40 and at idle aat 235 degree temp with all the cooling goodies thats as hotas she gets and thats when running 12+ lbs for extended periods,I also found Xtremes 4 core radiator with integral oil cooler helps keep avge conditions 45 seconds in 3rd/4th and 5th will elevate oil temp from around 210-235-240tops.
With the 10-40 I idle between 18-22 degrees so I feel (just a feeling) my bearings and bottom end are being well lubed.
If I am going to do super DUTY where my oil may hit 245 and with my cooler setup I dont recall seeing more than240 tops,so sometimes if I'm going on a 1200 mile trip in The TTb I will prematurely dump the oil in favor of 15-50 now my temps dont exceed 215-220 and my oil pressure at 210 degrees is hi 20's to low 30's.
I guess what Im trying to say is I dont trust a 60K motor thats been bitch slapped for 5 minutes oil temp within spec and oil pressure at 9 when I can afford to loose 20 ponnies in that car and cruise at 2200 rpm with 38 lbs. VS 24.
I hope this all makes sence and I'm not telling you'll to go with hi Viscosity oil,just being a Porsche and M Benz shop owner(long ago) Im not scared of castrol 20w-50,Dave S.