Engine Really Weird/erratic Oil Pressure

omarimoe · Jul 9, 2014

I know the factory gauges are notorious for being inaccurate but mine is really weird and it kinda makes me nervous. If i start the car when it's cold the gauge reads dead on half way up the gauge maybe a little higher. As expected when the car warms up a little bit the gauge drops to about the 2nd line from the bottom of the gauge. If i let the car get to running temp just idling the gauge will drop to about halfway between the bottom two lines. Now here is the funny thing it will randomly just die and show less than 0 pressure like if i just shut the car off/ignition off. If i blip the throttle the pressure will come right back up between the 2 bottom lines but after like 15 seconds will die again. if i turn the car off and immediately start it again the gauge will hold steady at the second line for about a minute and then die again. The car sounds and idles fine with no abnormal noises but it still makes me nervous. Bad sender? Gauge losing power or ground somewhere? I dont really want to go spend money on a mechanical gauge to be sure and no parts stores around me rent oil pressure testers. From the way it is acting does this sound like and oil pressure problem or a gauge/sender problem?

84Ttop · Jul 9, 2014

Only one way to know for sure and that is to actually check the oil pressure. Anything short of that would just be speculation, I'm sure that isn't what you wanted to hear though.
A quick search at summit racing yielded 350 different oil pressure gauges and they were priced as low as 6$. Spend 20$ and you can get something decent. If you don't want it in the car forever them keep it in your toolbox after you check it and you'll always have one just sitting around for the next time.

omarimoe · Jul 9, 2014

Yeah thats a good point cheap homemade tools that work are always good

stykthyn · Jul 9, 2014

I run autometer in my mustang but I have a 15 dollar sunpro in my jeep that works just fine. I have grown wary of all factory sending units.

omarimoe · Jul 10, 2014

I went and got a cheap sunpro mechanical gauge at pepboys today and hooked it up. Motor idles at 40psi when cold and between 12.50si and 17psi when hot. What is a good pressure/the right pressure for the car to be running at? Seems low to me I thought it should have been around the 25psi mark hot idle. With the car running at this oil psi cause more damage or is it just an old engine that will need a rebuild? Pressure seems to go up fine with throttle but comes right back down. I really dont want to rip this motor out and rebuild it I just had my other fox motor rebuilt.

jrichker · Jul 10, 2014

Oil pressure is supposed to run a minimum of 10 PSI per 1000 RPM according to Internet lore...

I'd start thinking about a high volume oil pump.

Before the Bozos start coming out of the woodwork with myths and fables about high volume oil pumps, here's what Melling, an OEM manufacturer of oil pumps has to say...

Thanks to Stangnet member bubba-dough for helping to educate all of us by finding this article...

http://www.mellingengine.com/Portals/5/pdf/pdf_catalog/high-volume-pumps.pdf You will need the Adobe Acrobat viewer which is also a free download – http://www.adobe.com/products/acrobat/readstep2.html

From the Melling site, for those who didn't follow the link & read the tech note...

High Volume Pumps: Advantages, Myths & Fables

Most of the stock automobile engines are designed to operate from idle to 4500 RPM. The original volume and pressure oil pump will work fine in this type of application. As the demands on the engine increase so does the demands on the oiling system and pump.

The oil pump's most difficult task is to supply oil to the connecting rod bearing that is the farthest from the pump. To reach this bearing, the oil travels from three to four feet, turns numerous square corners thru small holes in the crankshaft to the rod bearing. The rod bearing doesn't help matters. It is traveling in a circle which means centrifugal force is pulling the oil out of the bearing.

A 350 Chevy has a 3.4811 stroke and a 2.111 rod journal. The outer edge of the journal travels 17.5311 every revolution. At 1000 RPM, the outer edge is traveling at 16.6 MPH and 74.7 MPH at 4500 RPM. If we take this engine to 6500 the outer edge is up to 107.9 and at 8500 it is 141.1 MPH. Now imagine driving a car around a curve at those speeds and you can feel the centrifugal force. Now imagine doing it around a circle with a 5.581, diameter.

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.

mikestang63 · Jul 10, 2014

jrichker said:
Oil pressure is supposed to run a minimum of 10 PSI per 1000 RPM according to Internet lore...

I'd start thinking about a high volume oil pump.

Before the Bozos start coming out of the woodwork with myths and fables about high volume oil pumps, here's what Melling, an OEM manufacturer of oil pumps has to say...

Thanks to Stangnet member bubba-dough for helping to educate all of us by finding this article...

http://www.mellingengine.com/Portals/5/pdf/pdf_catalog/high-volume-pumps.pdf You will need the Adobe Acrobat viewer which is also a free download – http://www.adobe.com/products/acrobat/readstep2.html

From the Melling site, for those who didn't follow the link & read the tech note...

High Volume Pumps: Advantages, Myths & Fables

Most of the stock automobile engines are designed to operate from idle to 4500 RPM. The original volume and pressure oil pump will work fine in this type of application. As the demands on the engine increase so does the demands on the oiling system and pump.

The oil pump's most difficult task is to supply oil to the connecting rod bearing that is the farthest from the pump. To reach this bearing, the oil travels from three to four feet, turns numerous square corners thru small holes in the crankshaft to the rod bearing. The rod bearing doesn't help matters. It is traveling in a circle which means centrifugal force is pulling the oil out of the bearing.

A 350 Chevy has a 3.4811 stroke and a 2.111 rod journal. The outer edge of the journal travels 17.5311 every revolution. At 1000 RPM, the outer edge is traveling at 16.6 MPH and 74.7 MPH at 4500 RPM. If we take this engine to 6500 the outer edge is up to 107.9 and at 8500 it is 141.1 MPH. Now imagine driving a car around a curve at those speeds and you can feel the centrifugal force. Now imagine doing it around a circle with a 5.581, diameter.

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.

As always great info Joe. Most guys confuse a high volume with a high pressure oil pump- yes for the high volume, no for the high pressure pump on most DD cars.

omarimoe · Jul 10, 2014

Thanks for all the info man i wish i knew as much about foxes as i do Hondas. Is it possible to pull the pan and the pump without removing either the k member or lifting the engine? From what ive seen their cheap enough so I figure if it'll help get a little more life out of the engine why not.

jrichker · Jul 10, 2014

omarimoe said:
Thanks for all the info man i wish i knew as much about foxes as i do Hondas. Is it possible to pull the pan and the pump without removing either the k member or lifting the engine? From what ive seen their cheap enough so I figure if it'll help get a little more life out of the engine why not.

Been there, done that - You can do it in the car, but it is hard to do. The best way is to pull the engine.

Disconnect the battery at the battery ground terminal, remove the fan and fan shroud. Both motor mounts will need to have the large nuts that secure them to the frame removed. The trans mount will also have to be loosened, and it is a good idea to remove the drive shaft.

I also had to disconnect the cat pipes at the headers to get the engine high enough to remove the oil pan. Be prepared to have to drop the steering rack and disconnect the steering shaft. The flex coupling for the steering shaft needs to be disconnected before you can get the rack out. You should disassemble the coupling by removing the 2 bolts that hold it together Jack up the engine with a wood block under the oil pan and watch for things that bind or hoses/electrical wiring that may need to be disconnected. I put a couple of wood blocks between the headers and the frame to support the engine. You will likely need to jack up the rear of the transmission as well to get the required clearance.

Scrape the pan mating surfaces clean as possible - old gasket stuck to the surfaces are a source of leaks.

Get a high volume/heavy duty pump, and a replacement HD pump shaft.
If anybody tells you some fable about a high volume pump being a bad thing, see http://www.mellingengine.com/Portals/5/pdf/pdf_catalog/high-volume-pumps.pdf. The bad stuff is all Internet myth and tall tales Melling makes the pumps and they know what they are doing. HD Pump Shaft - FMS makes one, and ARP does too. When you install the pump, the funny looking washer thingy goes on the part of the shaft that fits into the hex socket in the distributor shaft. It keeps the shaft in place when you remove the distributor, which you will have to do to prime the pump. Forget to put it on, and the pump shaft can come loose and fall down in the bottom of the oil pan.

There is a one piece oil pan gasket which will help re-assembly if you can find it. If you can't get this gasket, use weather strip adhesive to secure the cork gasket to the pan rails and the rubber strips to the bearing caps. Use lots of Acetone or MEK to clean the gasket surfaces so the weather strip adhesive will stick good. Read the instructions on the adhesive carefully to make sure the gaskets are permanently stuck in place and won't move when you slide the pan in place. Use lots of blue silicone sealer on top of the front and rear rubber seals where they mate with the pan.

Fill with oil, replace the filter. Reconnect the battery, switch the ignition on to enable the gages, but DON'T crank the car. Remove the distributor and use a 1/4" hex socket to turn the pump counter clock wise (same direction as distributor rotation) until you see oil pressure (an external gage is a great help long about now). And keep turning for about 30 sec after you see the pressure come up. A reversible drill is the best tool to use to turn the 1/4" socket. The pressure should come up to about 50-80psi with cold oil. Once you see good pressure, check for obvious leaks, and then and only then, lower everything back into place and bolt down the mounts and anything else you had to take loose.

Re-install the distributor and set the timing with the engine running using timing light (don't forget to disconnect the SPOUT plug and reconnect it when finished) 12-14 degrees BDC is good. Start up and check for leaks, let it warm up and look again for leaks. It took me 2 days plus, but I am old and slow, maybe your granny is faster.

omarimoe · Jul 10, 2014

Does it matter what brand pump? Like a known good brand that works good on the 5.0's. Late model has f9rd racing hi volume pumps for like $50. Will that get the job done.

omarimoe · Jul 10, 2014

also am i going to need a new pan to clearance the bigger pump.

mikestang63 · Jul 10, 2014

omarimoe said:
Does it matter what brand pump? Like a known good brand that works good on the 5.0's. Late model has f9rd racing hi volume pumps for like $50. Will that get the job done.

I prefer melling. FRPP offshores most of its parts ftom China. ARP sells a good hardened oil pump shaft. While you have the engine out check the rear main seal as 90% of them leak. Get the Felpro one with the teflon sleeve for the crank- spring side in with a little coat of oil on the seal. Also check the other gaskets- valve covers, harmonic balancer seal. Much easier to change them now with the engine out of the car.

omarimoe · Jul 11, 2014

mikestang63 said:
I prefer melling. FRPP offshores most of its parts ftom China. ARP sells a good hardened oil pump shaft. While you have the engine out check the rear main seal as 90% of them leak. Get the Felpro one with the teflon sleeve for the crank- spring side in with a little coat of oil on the seal. Also check the other gaskets- valve covers, harmonic balancer seal. Much easier to change them now with the engine out of the car.

Thanks the melling is actually cheaper by $10. not sure when i want to do this yet as i really just got this car running and my other stang that i have been driving and is for sale started breaking up on me the other day. i feel like if im going to pull a motor it's getting overhauled and while it's out a new top end kit would be nice. idk i might just say screw it and let her eat for now and if i throw a rod then so be it. i also have a giant K&N oil filter on the car and ive heard running a smaller ford filter along with an oil additive like lucas could help with oil psi. ill have to get under the car in the next few days and see how big of a pain it would be to change out the pump with the engine still in the car.

Engine Really Weird/erratic Oil Pressure

omarimoe

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84Ttop

They make new pistons every day, so why worry?

omarimoe

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stykthyn

I want to measure mine. It doesn't look that tall.

omarimoe

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jrichker

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mikestang63

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Engine Really Weird/erratic Oil Pressure

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They make new pistons every day, so why worry?

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I want to measure mine. It doesn't look that tall.

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