Oil Pressure Question
07-06-2005, 06:58 AM
#21
Racer
Thread Starter
Member Since: Jul 2004
Location: Fredericksburg VA
Posts: 450
Likes: 0
Received 0 Likes
on
0 Posts
I guess it seems I need to try a little heavier oil first and if that doesn't work try the high volume oil pump. Thanks for all your responses, didn't realize this many people were having this problem. 
07-06-2005, 08:11 AM
#22
Le Mans Master
The mechanical oil pressure gauges on these cars (to 1973) are notorious for developing problems over time. The problem is that there is no oil flow through these gauges. The oil in the line going to the gauge (as well as the gauge itself) can remain there almost indefinitely. As you can imagine over time, in some cases many years, this oil will thicken and not allow the gauge to perform as designed. This can lead to suspicious indications and unnecessary alarm regarding the condition of the engine.
If you have a direct pressure reading gauge and are getting suspicious indications the first thing you should do is hook up a known good gauge and check the pressure indications as mentioned above. (When I say suspicious indications, I'm referring to indications that seem unusual with no secondary support. I.E.- anytime oil pressure drops to near zero, there should be an accompanying rise in valve noise, etc.) This is not that difficult to do and any skilled repair facility should have the equipment and capability for performing this test. The readings can then be compared to the in-car gauge.
If there is a significant disparity in the readings, it's time to replace the gauge or attempt to clean it. You can sometimes clean the gauge by removing it and spraying brake-clean into the opening to try and flush any congealed oil or debris out. I have tried this method a number of times with mixed results. It will appear to work properly only to have it malfunction again a few weeks later. Considering the time necessary to remove and install the gauge, it's often more cost effective to just replace the gauge. Most of the Corvette vendors can provide a new gauge or even service and repair your original.
It's also a good idea to flush the oil line from the back of the block to the gauge while you're doing this. If the line is in good condition and not leaking or kinked anywhere I usually flush it with brake-clean as well and dry it with pressurized air.
If your test gauge confirms the in-car indications, it's time to look at the condition of the engine or its oiling system, and you've been provided lots of areas to look above…
Good luck… GUSTO
If you have a direct pressure reading gauge and are getting suspicious indications the first thing you should do is hook up a known good gauge and check the pressure indications as mentioned above. (When I say suspicious indications, I'm referring to indications that seem unusual with no secondary support. I.E.- anytime oil pressure drops to near zero, there should be an accompanying rise in valve noise, etc.) This is not that difficult to do and any skilled repair facility should have the equipment and capability for performing this test. The readings can then be compared to the in-car gauge.
If there is a significant disparity in the readings, it's time to replace the gauge or attempt to clean it. You can sometimes clean the gauge by removing it and spraying brake-clean into the opening to try and flush any congealed oil or debris out. I have tried this method a number of times with mixed results. It will appear to work properly only to have it malfunction again a few weeks later. Considering the time necessary to remove and install the gauge, it's often more cost effective to just replace the gauge. Most of the Corvette vendors can provide a new gauge or even service and repair your original.
It's also a good idea to flush the oil line from the back of the block to the gauge while you're doing this. If the line is in good condition and not leaking or kinked anywhere I usually flush it with brake-clean as well and dry it with pressurized air.
If your test gauge confirms the in-car indications, it's time to look at the condition of the engine or its oiling system, and you've been provided lots of areas to look above…
Good luck… GUSTO
07-06-2005, 04:36 PM
#23
Drifting
Member Since: Nov 2001
Location: 68 427 4.11s Roadster
Posts: 1,469
Likes: 0
Received 5 Likes
on
5 Posts
To the above good post I should add my brother had an oil line blow on his car and this was way back when it was only a few years old, not like 30! He had on white pants and shirt before the oil line blew.
Hes been after my *** to change to a non interior gauge (isolator or electric) for years. Oil in the rug, general clean up and the big deal of he didn't go where he wanted when he needed to. And of course fixing the line.
Hes been after my *** to change to a non interior gauge (isolator or electric) for years. Oil in the rug, general clean up and the big deal of he didn't go where he wanted when he needed to. And of course fixing the line.
07-06-2005, 07:11 PM
#24
Drifting
Melling makes arguably the most reliable oil pumps around - they are I believe also the ones most aftermarket companies use as a core for thier modified pumps....
Here are a few things they say on their website....
Common Misconceptions on Oil Systems
OIL PUMPS PRODUCE PRESSURE. Oil pumps produce flow and the resistance to that flow produces pressure. The pressure relief valve limits the maximum pressure but does not do anything until the pressure has reached that point.
THE INLET SCREEN WILL KEEP DEBRIS OUT OF THE PUMP. Some of the new ones will but the majority have a 1/2" ID valve in the center or they have eight 3/16" X 1/2"slots around the edge of the screen. The valve or slots are there to allow cold thick oil into the pump. If you use thick oil with the new screens, you have a good chance of starving the engine of oil and ruining it.
I HAVE LOW OIL PRESSURE SO I'LL PUT IN A HIGH PRESSURE PUMP.The low pressure is usually caused by a leak or excessive wear in the engine. If the original pump has a 50 psi bypass and the engine will not get over 30 psi, then putting in a pump with a 75 psi bypass will not change a thing. You will still have 30 psi. You have to fix the leak or rebuild the engine.
SAME AS #3 EXCEPT I'LL PUT IN A HIGH VOLUME PUMP. The high volume pump does increase the flow so you will have some increase in pressure. However, you still have the original problem of a leak or worn out. The high volume pump just delays fixing the real problem. High volume pumps are for increased demands on the oil system such as higher RPM usage, racing, remote filters and or coolers, etc.
High Volumn pumps
The size of the gears or rotors determines the amount of oil a pump can move at any given RPM. Resistance to this movement creates the pressure. If a pump is not large enough to meet the demands of the engine, there will not be any pressure. Or if the demands of the engine are increased beyond the pumps capabilities there will be a loss of oil pressure. This is where high volume pumps come in; they take care of any increased demands of the engine.
Increases in the engine's oil requirements come from higher RPM, being able to rev faster, increased bearing clearances, remote oil cooler and/or filter and any combination of these. Most high volume pumps also have a increase in pressure to help get the oil out to the bearings faster.
That is what a high volume pump will do. Now let Is consider what it will not do.
It will not replace a rebuild in a worn-out engine. It may increase pressure but the engine is still worn-out.
It will not pump the oil pan dry. Both solid and hydraulic lifters have metering valves to limit flow of the oil to the top of the engine. If a pan is pumped dry, it is because the holes that drain oil back to the pan are plugged. If the high volume pump is also higher pressure, there will be a slight increase in flow to the top.
It will not wear out distributor gears. The load on the gear is directly related to the resistance to flow. Oil pressure is the measure of resistance to flow. The Ford 427 FE "side oiler" used a pump with relief valve set at 125 psi and it used a standard distributor gear. Distributor gear failures are usually caused by a worn gear on a new cam gear and/or worn bearings allowing misalignment.
It will not cause foaming of the oil. With any oil pump, the excess oil not needed by the engine is recirculated within the pump. Any additional foaming is usually created by revving the engine higher. The oil thrown from the rod bearings is going faster and causes the foaming. This is why high performance engines use a windage tray.
It will not cause spark scatter. Because of the pump pressure there is a load on the distributor gear. The number of teeth on the oil pump gears determine the number of impulses per revolution of the pump. In a SB Chevy there are seven teeth on each gear giving 14 impulses per revolution. At 6000 RPM the oil pump is turning 3000 RPM or 50 revolutions per second. To have an effect on the distributor, these impulses would have to vibrate the distributor gear through an intermediate shaft that has loose connections at both ends. Spark scatter is usually caused by weak springs in the points or dust inside the distributor cap.
High volume pumps can be a big advantage if used where needed. If installed in an engine that does not need the additional volume, they will not create a problem. The additional flow will be recirculated within the pump.
Here are a few things they say on their website....
Common Misconceptions on Oil Systems
OIL PUMPS PRODUCE PRESSURE. Oil pumps produce flow and the resistance to that flow produces pressure. The pressure relief valve limits the maximum pressure but does not do anything until the pressure has reached that point.
THE INLET SCREEN WILL KEEP DEBRIS OUT OF THE PUMP. Some of the new ones will but the majority have a 1/2" ID valve in the center or they have eight 3/16" X 1/2"slots around the edge of the screen. The valve or slots are there to allow cold thick oil into the pump. If you use thick oil with the new screens, you have a good chance of starving the engine of oil and ruining it.
I HAVE LOW OIL PRESSURE SO I'LL PUT IN A HIGH PRESSURE PUMP.The low pressure is usually caused by a leak or excessive wear in the engine. If the original pump has a 50 psi bypass and the engine will not get over 30 psi, then putting in a pump with a 75 psi bypass will not change a thing. You will still have 30 psi. You have to fix the leak or rebuild the engine.
SAME AS #3 EXCEPT I'LL PUT IN A HIGH VOLUME PUMP. The high volume pump does increase the flow so you will have some increase in pressure. However, you still have the original problem of a leak or worn out. The high volume pump just delays fixing the real problem. High volume pumps are for increased demands on the oil system such as higher RPM usage, racing, remote filters and or coolers, etc.
High Volumn pumps
The size of the gears or rotors determines the amount of oil a pump can move at any given RPM. Resistance to this movement creates the pressure. If a pump is not large enough to meet the demands of the engine, there will not be any pressure. Or if the demands of the engine are increased beyond the pumps capabilities there will be a loss of oil pressure. This is where high volume pumps come in; they take care of any increased demands of the engine.
Increases in the engine's oil requirements come from higher RPM, being able to rev faster, increased bearing clearances, remote oil cooler and/or filter and any combination of these. Most high volume pumps also have a increase in pressure to help get the oil out to the bearings faster.
That is what a high volume pump will do. Now let Is consider what it will not do.
It will not replace a rebuild in a worn-out engine. It may increase pressure but the engine is still worn-out.
It will not pump the oil pan dry. Both solid and hydraulic lifters have metering valves to limit flow of the oil to the top of the engine. If a pan is pumped dry, it is because the holes that drain oil back to the pan are plugged. If the high volume pump is also higher pressure, there will be a slight increase in flow to the top.
It will not wear out distributor gears. The load on the gear is directly related to the resistance to flow. Oil pressure is the measure of resistance to flow. The Ford 427 FE "side oiler" used a pump with relief valve set at 125 psi and it used a standard distributor gear. Distributor gear failures are usually caused by a worn gear on a new cam gear and/or worn bearings allowing misalignment.
It will not cause foaming of the oil. With any oil pump, the excess oil not needed by the engine is recirculated within the pump. Any additional foaming is usually created by revving the engine higher. The oil thrown from the rod bearings is going faster and causes the foaming. This is why high performance engines use a windage tray.
It will not cause spark scatter. Because of the pump pressure there is a load on the distributor gear. The number of teeth on the oil pump gears determine the number of impulses per revolution of the pump. In a SB Chevy there are seven teeth on each gear giving 14 impulses per revolution. At 6000 RPM the oil pump is turning 3000 RPM or 50 revolutions per second. To have an effect on the distributor, these impulses would have to vibrate the distributor gear through an intermediate shaft that has loose connections at both ends. Spark scatter is usually caused by weak springs in the points or dust inside the distributor cap.
High volume pumps can be a big advantage if used where needed. If installed in an engine that does not need the additional volume, they will not create a problem. The additional flow will be recirculated within the pump.
07-10-2005, 03:48 PM
#25
Instructor
Member Since: Oct 2004
Location: Hattiesburg MS
Posts: 173
Likes: 0
Received 0 Likes
on
0 Posts
Discovered something weird yesterday and need to understand why. Since I put the new Edelbrock carb on the engine I have noticed a sucking sound just after turning the engine off. While running there is so much vac on the valve covers that you can barely remove the oil filler cap and it bleeds off when the engine is stopped (sucking sound). Yesterday I unplugged one of the PCV valves and plugged the line going to it. This was done due to someone suggesting that I run only one PCV valve and a breather on the other side. In the past I noticed that the oil pressure would go up if I pulled the oil filler cap off so I checked it while only running one of the PCV valves as described above. The oil pressure has not gone below 30 psi at idle since this was done vs. about 10 psi with both valves connected. While driving it now stays about 50 - 55 psi. Can crankcase vac have an effect on oil pressure? If not, someone please help me understand what is going on. 
