I hope this is on the right board..if not..it'll be locked. ah well..

What's my oil pressure supposed to be at for cruising? IE 0-50 MPH..
Occasionally when I'm driving, it will drop down to 10 and below when I'm slowing down..is this normal? Should it be between 30 and 40 at all times? I have the 140 gauges with the numbered oil pressure gauge..I've owned two 3gens before this and I never noticed this happening before..but they were both 3.1's while this new one is a 5.7..

 

I think it's >18psi at 2000RPM, but I forget right now.

It's normal for it to drop on decel, but not drastically. Most people say to check the sender before taking the gauge reading to heart.

 

an old rule of thumb was 10 psi per 1000 rpm that the motor spun at operating temperature, 2500=25 psi, 5000=50psi but by the book-mitchell on demand-and the factory manual states that 50 to 65 psi at 2000 rpm is what they want to see (5.0 and 5.7) but there are a load of longlived small blocks running around and healthy with less than the book wants to see.i would reccommend to hook up a known good mechanical gauge and verify what the dash is telling you first. i will bet your ok in the pressure dept. and the sender is going bad or someone used teflon tape and it is stuck in the small oil hole in the end of the sender. BTW-even the new factory ac delco replacement senders are made in taiwan-GRRRR

 

Below 10 psi is not normal and may, I emphasize MAY, indicate a problem.

Oil pressure is dependent on a number of variables:

1. Bearing Clearances
2. Oil Weight
3. Oil Temperature
4. Rod Side Clearances
5. Engine RPM
6. Oil Pump Type and Condition (Standard Vs High Volume Vs High Pressure Vs High Volume/High Pressure
7. Lifter to Lifter Bore Clearances
8. Any maybe some others I haven't thought of.

As a general rule of thumb, with a performance engine at normal (fully warmed up engine) operating temperature, with standard weight oil (10w30 - 10w40) you'd want to see about 20 psi at idle. The old '10 psi for every 1000 RPM the engine turns' rule that you see in some of the magazine articles is sort of misleading.

Crusing along the interstate in overdrive at 70 MPH and the engine turing 2000 RPMs, you'd really want to see 40 psi or more. So much for the 10 psi per 1000 RPM that some mags tout.

Those are MINIMUMS too. Some engines - not Chevys - need 125 psi minimum to keep the bearings alive.

If your oil pressure is dropping to below 10 psi when you slow, the cause could be a low oil level in the pan. Pressure drops when the oil sloshes away from the pickup and the pickup sucks air.

Another possibility is oil aeration from having too much oil in the pan (crank whips the oil into a froth so the oil pump is sucking an oil/air mixture).

Inaccurate or malfunctioning oil pressure gauge.

Or some mechanical problem.

Make sure you have an accurate gauge and watch oil pressure like a "hawk" - oil is the life's blood of an engine.

Hope this helps.

Jake

 

its not just magazines though, ive been in the auto repair trade for 17 years and have owned my shop now for just over 4 years and for what ive seen and experienced still where small block chebbys are concerned the old 10 psi rule, unless its puffin out the oil filler hole, or rattling the bottom end. generally keeps the motor alive. just ask this-"when was your last oil change sir(maam)" blank stares or ummm usually means something too.

 

Sir! 4,346 miles ago, sir!

No blank stares here..

 

yer 1,346 overdue. ow

 

As with most things when it comes to engines, if you ask ten people you'll get eleven opinions.

Let me give you a few suggestions on how to resolve this dilemma:

Check the dyno results that are posted in some of the auto magazines. Some of articles give very detailed information and include the oil pressure at the various RPMs run in the test.

Check some of the websites that sell warranteed performance crate engines and see what pressures the engine builders are setting their engines to. The don't want "come backs" so they've 'scienced-out' the oil pressure issue.

Next time the Winston Cup or NASCAR boys are on TV, take a close look at their oil pressure readings when an inside the car camera shot is taken. Try to catch a reading in the pits, too, with the engine at idle.

Check the archive files on this and some other sites; like http://forums.corvetteforum.com/zeromain (where I usually post since I've got a Vette) and see what the general consensus is.

I think you'll find that virtually no one runs five and a half psi of oil pressure at a 550 RPM idle speed. I'm betting too that virtually none adhere to the 10 psi per thousand RPM rule of thumb either; all will exceed this.

A little too much will only cost you a few ponies, but too little will cost you an engine.

Just trying to help.

Jake

 

i have a similar problem with my oil pressure, at cold idle/cruise, it is 45 psi, cruising warm, it is at 30-35, and when i sit at idle warmed up, it reads 0psi. the car doesn't die or knock, but it does idle down to like 500 rpm. could the fact that my oil pan is dented in slightly have something to do with it or could it be the sending unit or pump or pickup screen?
someone help
it just had the intake resealed, and it didn't do this before

 

im with jakejr on this one, that rule of 10psi per 1000rpm is nonsense. id be damn concerned if my gauge ever even dropped to 10psi, much less zero. during idle, warm or cold, both of my L98 cars never see below 35psi of pressure. both run mobil 1 10w30, the vette is a factory 100k mile motor, and the iroc-z has a new motor.

 

If your gauge is showing zero and you haven't developed any bearing problems, it's almost certain that the gauge is inaccurate. If the gas gauge shows empty but the engine's still running there's got to be at least a little gas in the tank, right?

Zero oil pressure is going to rear it's ugly head at some point, in spite of what those idiot informercials say. "Look; we drained all the oil and even removed the oil pan and the engine's still going strong" Yea, Right!

The dented oil pan could be part of the problem if the pan got dented enough to tweak the pickup. The pickup could be either partially closed or is sucking air because it's no longer tightly sealed where it enters the pump.

I know it's a real PIA to drop an "F" body's pan, but I would.

Hoped this helps.

Jake

 

nonsense-whatup with that cr-p check the generals service bulletins 88-114-6 and 87-275-8c i think an error here is basing your judgement call on the 2 cars in the driveway and in addition, maybe the ones that your buddies have. but maybe being damn concerned is important too.

 

Grumpy: as far as him being over due? ever consider one may be running synthetic?

 

you got me

 

hey-wait a minute-nonono-one of the tasks that motor oil is assigned is to keep the contaminants (by products of combustion, chunks o' metal- hopefully for all concerned here that they are small, leave the big ones for the HOTRODHONDACROWD\vomit sounds-and other misc.items left behind from everyday use of your camaro) suspended within it so with an oil change most contaminates flow out w/the old oil instead of clinging to the internals. you are absolutely correct that synthetic oil is without a doubt the best single thing to ensure longevity for your powerplant, it will still carry the contaminates that accumulate over the extended period that you choose to leave it within the crankcase. so in that regard it is up to the owner to decide how it is handled. you know that we are actually both correct about this and it is one of the things that we can decide ourselves how we want to handle it. i guess, ultmately, if we extend the reasoning here to the extreme we would have oil tankers following us around hooked up to our rides circulating fresh oil always, but as in most things in life a certain amount of compromise is required. i wish i could run synthetic in my 400 but cant with those var.duration crane lifters i got-seeya

 

Is changing the sender hard, and how much does one cost?

 

The sender is easy to replace. IIRC you need a 7/16 or 9/16 open end wrench. You may have to remove your plenum and drivers side runner to get at it. It is that bronze cylindrical thing on the back of your block near the distributor, drivers side.

 

unless it is a 5,0 or 5.7 from 1989 and up because the sender for those years is on the lower left side of the block, just above the oil filter boss. also incorporates the f.pump switch

 

At the risk of continuing this back and forth on proper oil pressure, (and incurring the wrath of some) let me preface my comments by saying that in the final analysis it's YOUR engine and you can pretty much do what you want.

Most already know this stuff, but for the benefit of those who don't here goes.

Ever stop and think about what's actually going on inside a running internal combustion engine?

Some don't realize it, but the most important function of motor oil, other than preventing metal to metal contact, is the carrying away of heat. Transferring heat from the oil to the surrounding block surfaces, then to the coolant, the radiator and dispersed by airflow.

Ever wonder why it's a NO-NO to install a bearing with oil on its backside? Interferes with the transfer of heat.

Heat's the enemy!

Most of what we do to an engine centers on two things: Reliability and power production. We don't want it to break and we want to make good power. Sure, there are those concerned with gas mileage, smooth ride, etc., but they don't usually buy performance oriented cars like "F" bodies, Mustangs or Vettes do they? Chances are good that they don't frequent this board either.

So my comments are for those of us who are 'like-minded'.

In dealing with reliability heat's the enemy of a gasoline burning engine. Excessive heat does terrible things to metal, shortening the part's life span and, ultimately, keeps us digging into out pockets for $.

Absent the ability to carry away heat, oil soon breaks down and will no longer do it's job. Synthetics are better than the Saudi stuff at handling high heat since it can withstand much higher temperature for much longer periods of time before being adversely effected.

Your average SB Chevy engine, built to factory specs has a bearing clearance in the area of .002/.0025. In most cases the minimum is the preferred clearance.

If you can't visualize that thickness (thinness), just grab a set of feeler gauges, thumb through them til you find one stamped .002 and take a good look at it.

Ideal clearance varies somewhat on performance engines though and also varies by engine family. Grab an old Chilton, Motors Manual and take a look at the clearances. Generally, the higher HP engines tend to have slightly larger recommended clearances.

So .002/.0025 is the clearance between the crankshaft journals (mains and rods) and the bearing surfaces and is filled with oil under pressure. That very thin layer of oil is all that's keeping your high dollar hummer alive.

Absent that clearance, the crank journal will come in direct, metal to metal contact with the bearing and diaster will soon follow.

As an engine is running, bearing stress is not constant. It varies depending on what portion of the stroke is involved - intake, compression, power, exhaust or somewhere in between.

Oil holes are positioned in the crank to allow oil to be introduced to that small clearance area at a point just before maximum stress is experienced.

Remember that layer of oil protection is only .002 or so thick.

As an engine is making power, the rod/piston combination is constantly trying to push the crankshaft out the bottom of the block. Hence, four bolt caps, splayed outer main bolt configurations, steel billet materials, etc.

In spite of how substantial a crankshaft may appear when you lift one with your bare hands, under load, the crank does flex. When it flexes, the bearing clearances want to decrease, resisted by that very thin layer of non compressible oil.

So, yes, under ideal conditions, you could drive coast to coast with 5.5 psi of oil pressure at idle and 10 psi per thousand rpms, but you have no margin for error; no safety net. If anything adverse happens, you (or more precisely your engine) would be out of luck.

It' sort of like living from paycheck to paycheck with no savings. As long as the paycheck keeps coming in on a regular basis and it meets your expenses, everything's fine. But don't let some unexpected financial situation occur - like getting layed off, or the furnance quitting in the dead of winter - then you'll be in for trouble.

Oil pressure can be looked at in the same way. If you have 5.5 psi/10 per thousand pressure and for some unexpected reason pressure falls a tad or the crank flexes just that little bit too much, you've got no margin of safety.

I think we all know what happens then. The journal touches the bearing, the friction almost instantly causes extreme heat to develop, the bearing material begins to melt and is torn away; the journal gets scored and the ever increasing friction and heat causes the bearing to spin in the bore.

With the mains, the oil hole in the main bearing will no longer aligned with the oil hole in the block so now even if you had 200 psi of oil pressure it wouldn't do any good cause there's no way for it to get to the bearing surface, which would be damaged beyond hope by now anyway.

With the rods, the drastically increased clearances caused by the wearing away of the bearing surface material causes that dreaded knock sound.

At low RPM with light load, the engine would slowly seize tight. At high RPM and high load a rod gets kicked out the side of the block or down through the oil pan. Bad news in either case.

Sorry this was sooooooo long, but I'd hate to cut corners on something as important as oil.

As I said, though, it's your engine.

Jake

 

lmao, nice novel.

 

detonation-uncontrolled-will always "break thru" the few molecules of protection oil offers usually a piston will let go first though. h.d. trucks seem to use bottom ends up before the top goes away. from what i have seen.

 

ive been working on cars a long time, and my opinion was not based on the two cars in the driveway. ive seen it in numerous cars. i am aware that most every repair manual states that 10psi per 1000rpm rule, but i still very strongly disagree with it, and i always will. plus, you have to take into account, when was that "rule" stated? probably while solid mechanical lifters were the only option. i would never be satisfied with an engine with 10psi of pressure at idle.

 

ok

 

Speaking of oil pressure: Ever wonder why so many production cars come with idiot lights or gauges that don't indicate actual numbers?

Numbers make car owners nervous.

Say you're driving down the interstate with a digital gauge or one that has actual psi or temp numbers on the gauge face. Now you exit and come to a stop and the numbers on the gauge start to climb.

Nervous in the Service time: most car owners think something's wrong and head off the the Service Department to complain. The Service Department manager does his best to explain that it's normal, but the owner remains skeptical about the reading and is a dissatisfied customer.

Now, take a look at the vast majority of cars and all you'll see is a needle that points to an unidentified area on the gauge. As long as the needle is in the "middle" of the gauge, the driver is unconcerned.

Those needle type gauges are less responsive too, whereas the digital gauge will change numbers up and down pretty quickly.

Car manufacturers learned a long time ago that in some cases less information is better than full disclosure.

 

right on jake jr. i never thought about it that way-but i do believe that you are on to something there. where did you hear about that concept? its got to have been (like you say) a way to keep customers from nitpicking the car to bits as the warranty repair techs try to fix something that aint broken. a light makes it simple- good/bad- off/on 2 choices only.

 

For better or for worse, it's something that I theorized after reading soooooooo many posts on this and other boards about gauge "numbers".

I believe that most folks like to see steady numbers that don't fluctuate, but a really responsive, sensitive gauge will move around quite a bit.

From reading lots and lots of posts, I've concluded, too, that most folks' "nervous meter" begins to peg when temp readings cross the 200 F level, as if when temps climb above 200 F it's time for concern but below 200 everything is fine and dandy.

In fact, when it comes to coolant and oil temps, above 200 is generally better. 220 oil temps insure good flow and moisture can be eliminated from the oil.

When coolant temps are too low, like 160/180 F which a lot of guys shoot for, proper block expansion and stabilization- hence ring seal - isn't achieved. Piston to wall isn't correct and ring seal suffers.

Engines are always fully warmed and temps stabilized before dyno pulls are made and the I believe the "Go fast boys" of Winston Cup and NASCAR, etc. shoot for 210 coolant temps; and oil temps probably higher.

The trick is to keep the intake air temp as low as possible - like using ice packs on the manifold between rounds; air gap manifolds,oil splash shields, etc. - but keep the block and head temps up.

The problem with high temps mainly involves the transfer to heat to the air intake charge which lowers the air density and costs power.

I currently own a Vette (please don't hold that against me) but I've owned lots of "F" bodies all bought brand new and all Trans Ams - 72, 76, 80 (turbo), 86 and a 96. The later year variety all ran 220 F coolant temps right off the showroom floor and none ever skipped a beat.

Just my thoughts.

Jake

 

I had the same problem with my GTA. After getting the heads redone (a while back b4 I knew much about cars), about 3 months after that, the oil pressure would drop to 0 at idle. So I went ahead and changed to a high vol/preseure oil pump.

Did nothing. So eventually, it diveloped the infamous knock, which got worse and worse.

Just recently, I pulled the engine, and competely dis assembled it. What I found was that the bearing faces, and the crank journals were scored. Looked like a "Brake rotor" type of scoring. The bearings were not really worn down, and the oil journals were still present.

I still to this day dont know what caused this. Oil was changed EVERY 3k, and there was nothing at the bottom of the pan. The car did how ever seem to have a slight temp problem. Always ran 10w30.

Im sure the constant starting up of the car when I used to deliver pizzas 3 years ago didnt help any. I gotta admit though, I did drive her pretty hard at times.

Any ideas on what caused it? Not like it matters now, but Im still curious.

 

I wish I could say with any degree of certainty what caused your bearing problems, but I can't

The four main causes of bearing problems are:

Improper Clearances

Trash

Detonation

Starvation

Over-Heating
That's five isn't it?

Since your engine was obviously running okay before the head work I'll have to assume the clearances were okay.

I know guys who have worked on Chevy engines since Hector was a Pup and still don't wash, wash and re-wash their engine when it comes from the machine shop. They just bolt it together and fire it up.

Never ceases to amaze me what some guys do.

Grumpygreaseape hit on it identifing detonation as a cause. Some like to refer to it as "ping" or "pre-ignition" as if changing the name somehow lessens the destruction it causes. One sure way to tell is when you pull a main or rod cap and the bearing falls out into your lap, you can bet the engine has experienced detonation. Detonation changes the shape of the bearing from half circle to "U" shape. "Fly sh**" on the plug porcelain is another tip off.

I know some guys who run straight 50W oil in their race engines. You can imagine how poorly 50W flows when cold - even when warmed up it won't win any flow awards - so they've resorted to a little trick that is supposed to help. They'd crank the engine until pressure showed up on the gauge, then hit the ignition switch fire it up. The thinking is that an engine cranking with no load doesn't stress the bearings. Never ceases . . .

Most now know (from the commercials if nothing else) that most engine wear occurs on startup; so repeated startups amplify the wear. If all else was right with the engine, I can't believe that delivering pizzas killed it.

Once oil has over-heated it doesn't come back, so you'll need a fresh load. Heat changes the molecular structure. Better add a caveat here: Not sure about synthetic, but I wouldn't chance it.

Once it hits 270 F I'd dump it and reload. For me that's an arbitrary temp and, like most of my opinions, is totally unsupported.

Hope this helps.

Jake