Oil pressure problems

[HotRodScottsdale]

I got a 1984 silerado, 350 small block bored 30 over forged crank with 68 Camaro heads and gear driven timing. All the work done before I got the truck, the previous owner ran royal purple 5w30 oil and I noticed the oil pressure gauge was all over the map. Idled around 20psi and jumped to max 40psi with any acceleration. I changed the oil and didn't see any metal and switched to royal purple 10w30 and it helped for a week and then it jumped all over again but truck ran and sounded amazing so I ignored it and kept driving the truck as a daily. Now yesterday day I noticed the gauge dropped to 10psi and only went up 1 or 2 psi with acceleration, I went to pull over and it snapped back to jumping again. Now today leaving work it dropped to 10 psi again and won't come back.

Where do I start looking? Oil on the dip stick looks good, motors not making any knocking or strange sounds, truck still runs great so I'm hoping it's a grounding issue or something with the pressure sensor.

Anyone have this issue?

[farmall]

Try a mech test gauge or the pickup tube is not sealed to the pump.

[sweetk30]

If a electric sender is going bad it can do weird crap .

Try new or verify with good QUALITY mech guage .

[Tx Firefighter]

Old mechanic advice here...

"You never have an actual oil pressure problem until you've verified it with a mechanical gauge".

[Nick_R_23]

+1 on first step being verification of actual oil pressure with a QUALITY mechanical gauge. It may just be as simple as a faulty sending unit/gauge, but multiple things can be the cause of low oil pressure, such as:

*Worn main bearings
*Worn connecting rod bearings
*Worn camshaft bearings
*Damaged/faulty oil pump, or broken/stuck relief valve and spring
*Improperly clearanced or secured oil pickup tube, or tube is cracked
*Oil sludge or debris blocking pickup tube
*Clogged oil passageway leading to sending unit
*Faulty oil filter bypass
*Oil filter failure by internally collapsed filter media (usually Fram or other cheap filters)
*Improper length dipstick causing oil foaming due to incorrect oil level.
*Internal oil pressure leak (internally cracked block)
*Improperly secured distributor or distributor-oil pump drive shaft retainer missing.

[Corts60]

Agree with all above. Always verify with a mechanical gauge that is quality.

[HotRodScottsdale]

Than you everyone for all the tips and advice. I will buy a mechanical gauge and try that first. I'm hoping it's just the sensor or the gauge. The factory one is electrical I believe and the wiring is kinda rough in this old truck

[Pontiac1976]

I agree with all. If the 84 have the factory gages it should be electric. Since the motor had a up grade I would check the mechanical sender see how new it look betting dirt in it moving around. ( But run a mechanical gauge bypass test some how to your motor make sure you do have pressure first.) Still could be bad gauge, If you still good pressure check the electric connection +,- area's then the sending unit then gauge. You can do a test with a Dist. Test shaft buy or make your own out of a old (DISTRIBUTOR Shaft) so you do not have to run the motor.

[Dleslie212]

Originally Posted by Corts60

Agree with all above. Always verify with a mechanical gauge that is quality.

I have a mechanical gauge on mine, although it’s a cheap one. But I’ll start off with around 40-50 psi when cold, and after running awhile can drop as low as 5-10 while idling. How big of a problem is this?

[Dead Parrot]

Originally Posted by Dleslie212

I have a mechanical gauge on mine, although it’s a cheap one. But I’ll start off with around 40-50 psi when cold, and after running awhile can drop as low as 5-10 while idling. How big of a problem is this?

Assuming a mostly stock motor, probably not much. My 350 with OEM mechanical gauge will go to near 60 psi when cold and once hot will be around 1/4 scale or about 15 psi at idle. 10-30 oil.

Might check your idle speed. A few rpms can sometimes make a big difference in idle speed oil pressure.

[truckin 79]

Originally Posted by Dleslie212

I have a mechanical gauge on mine, although it’s a cheap one. But I’ll start off with around 40-50 psi when cold, and after running awhile can drop as low as 5-10 while idling. How big of a problem is this?

My 79 will do the same thing and have been wanting to throw a gauge on it to double check. When warm at idle my stock gauge will just be a tick above the 0 psi mark. I do not hear any ticking or thumping so I assumed oil pressure is okay. This is good info to know

[Nick_R_23]

Originally Posted by Dleslie212

I have a mechanical gauge on mine, although it’s a cheap one. But I’ll start off with around 40-50 psi when cold, and after running awhile can drop as low as 5-10 while idling. How big of a problem is this?

It’ll become a bigger problem. That’s an indication of high bearing clearances, so you most likely have worn main, rod, or cam bearings in your engine. An engine can live at 5-10 psi at idle, but it’s an indicator that it’s a good time to think about a rebuild.

[Corts60]

An old school rule of thumb for oil pressure is 8 lbs per 1000 RPM. But, personally, I would be concerned that there is too much bearing wear if oil pressure drops below 15 psi at warm idle.

[Pontiac1976]

Most idle factory truck/car warm would be 550-650 oil pressure will be low. The oil pressure should have a normal pressure reading and normal dropping pressure and a normal steady low end pressure when warm. *( for your own truck/car) If it running ok the parts that may be in the truck/car there lot of things that come in to play new oil, old oil. thick oil, thin oil. Miles on motor it helps to know your truck/car motor. how much metal in the oil normal or above normal lots of metal flakes. How new of a rebuild on motor a breaking motor will show a little more wear on break in fore the first 500miles. Take the coil wire off remove valve covers put some rags around heads turn truck/car over about 1-2 min or till you see oil pushing out the push rods at the rockers arms. oil come up the you got working pressure. Then you know getting oil up. So then if you tested gauge say good sending unit, oil, dirt in the old sending unit, or gauge. or if the oil dribbling out only maybe oil pump or dirt in the pump or pick up plugged or missing or pump wore out. How tight the motor build. To thick of oil will make you loose HP. Most new oils now a days are thinner and are synthetic. RPM will change Oil Pressure big time, If you rev up to 1000-1200 RPM you should see it go up a fair amount unless you pump failure ( same thing you do after oil change start up. To make sure oil get up and you have pressure. OIL viscosity when it starts to break down oil pressure will drop a little more and more at first once you know you oil normal temp where it sits before and after warm up idle and drive and RPM's you can see the viscosity break down check mile know when to change oil and this is for reg oil and synthetic oil because once viscosity breaks down it not lubing the motor well at all.

[farmall]

Originally Posted by Pontiac1976

Most idle factory truck/car warm would be 550-650 oil pressure will be low. The oil pressure should have a normal pressure reading and normal dropping pressure and a normal steady low end pressure when warm. *( for your own truck/car) If it running ok the parts that may be in the truck/car there lot of things that come in to play new oil, old oil. thick oil, thin oil. Miles on motor it helps to know your truck/car motor. how much metal in the oil normal or above normal lots of metal flakes. How new of a rebuild on motor a breaking motor will show a little more wear on break in fore the first 500miles. Take the coil wire off remove valve covers put some rags around heads turn truck/car over about 1-2 min or till you see oil pushing out the push rods at the rockers arms. oil come up the you got working pressure. Then you know getting oil up. So then if you tested gauge say good sending unit, oil, dirt in the old sending unit, or gauge. or if the oil dribbling out only maybe oil pump or dirt in the pump or pick up plugged or missing or pump wore out. How tight the motor build. To thick of oil will make you loose HP. Most new oils now a days are thinner and are synthetic. RPM will change Oil Pressure big time, If you rev up to 1000-1200 RPM you should see it go up a fair amount unless you pump failure ( same thing you do after oil change start up. To make sure oil get up and you have pressure. OIL viscosity when it starts to break down oil pressure will drop a little more and more at first once you know you oil normal temp where it sits before and after warm up idle and drive and RPM's you can see the viscosity break down check mile know when to change oil and this is for reg oil and synthetic oil because once viscosity breaks down it not lubing the motor well at all.

I think I need medication after trying to read that.

[sweetk30]

Originally Posted by farmall

I think I need medication after trying to read that.

glad most forums now dont do options for colors and we need paragraphs .

hate to say it but i skip over funky color text posts . my eyes cant do it like they did years ago .