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Author Topic:   oil psi problem
11dirt
Dirt Roller

Total posts: 5
posted December 08, 2005 08:53 AM  
when running on the track oil psi holds up find, but right after coming off the track and going through the pits the psi will drop down to the 5-10# for just a couple of seconds and then comes back up where it is suppose to be. i can understand what's going on if it is doing this when turning rpm's on the track but not afterwards under low rpm's. any idea's?

racer2
Dirt Freak

Total posts: 369
posted December 08, 2005 09:00 AM  
pick up fell off.jmo

FFMM
Dirt Roller

Total posts: 21
posted December 08, 2005 09:05 AM  
how far does your rpm drop when you come off the track? are you changing gears? doesnt sounds like a problem

Speedracer92
Dirt Forum Racer

Total posts: 79
posted December 08, 2005 01:56 PM  
Sounds pretty normal to me. When you pull off the track and drop your RPM's to an idle range when the motor is hot, your oil pressure usually drops off.

11dirt
Dirt Roller

Total posts: 5
posted December 08, 2005 02:03 PM  
but what we can't figure out is the psi only drops for a couple of seconds then it comes back up.

FATBOY90
Dirt Full Roller

Total posts: 66
posted December 08, 2005 02:39 PM  
its normal dont worry about it

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FATASS RACING

awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 09, 2005 08:19 AM  
let me toss this out there, ever thought maybe because at racing speed it's say 70 psi and after you get off the throttle the pressure out of the pump drop to say 30psi that because of the differance the gauge doesn't read correctly?? because the pressure inside the gauge is greater than the pressure of the pump out-put the oil has to go backward for a secound or two?? I'm not saying THIS is going on...... but this topic seems to come up every year and everyone agress this is NOT a problem, and this is NORMAL........but i'm the type person the needs to know WHY....

like I stated the pressure in the gauge being greater than the pressure out-put of the pump is the only thing that makes sense to me. forcing the oil to go backward. I would anjoy hearing other peoples thoughts on my thought...........

[This message has been edited by awkwardjeff (edited December 09, 2005).]

11dirt
Dirt Roller

Total posts: 5
posted December 09, 2005 11:34 AM  
awkward jeff, so far you have the most sensible answer. i'm like you , normal or not i want to know why things like this happens. thanks.

stockcar5
Dirt Forum Champ
Total posts: 595
posted December 09, 2005 03:40 PM  
i had the EXACT same thing happen this year. pickup was almost all the way off...was ok for the race but dipped when i hit the brakes hard in the pits. better pull the pan for some piece of mind if anything. 5-10psi is NEVER normal.

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www.sathoffracing.com

racer2
Dirt Freak

Total posts: 369
posted December 11, 2005 08:43 AM  
mine will drop to 25 or 30 after the main

wareagle87
Dirt Roller

Total posts: 11
posted December 11, 2005 10:55 AM  
I may be way off here, but oil in an incompressible fluid. Therfore the pressure at the pump dischange will be felt at the gauge. Again, I am no physicist, but....

James Ott
Dirt Maniac

Total posts: 170
posted December 11, 2005 11:14 AM  
Wareagle you are correct but air trapped in the line is compressable. oil gauge lines should be bled. It is tough to get the air out of a gauge as well. Oil does not really flow through the line anyway it is a dead end in the guage. The oil is only reacting to the pressure it sees at the point of connection in the oiling system of the motor. Right now im using 1/4" tubing because our track does not allow plastic lines and it seems to work well. I'm going to try the small stuff next season and see if it makes a difference. I'm thinking the 1/4 line maybe a little more responsive

racer2
Dirt Freak

Total posts: 369
posted December 11, 2005 04:21 PM  
the small line made my guage so slooooooooooo

[This message has been edited by racer2 (edited December 11, 2005).]

awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 12, 2005 03:50 AM  
oil is a incompressible fluid? In my thoughts I didn't think it compressed, it has pressure at the gauge, and if the pressure on the other end of the line leading to the gauge drops the oil does go backward to some degree. Hook a ball valve into your oil pressure line, rev the motor until you have 70 psi on the gauge and shut the ball valve, now disconnect the line point the line at your buddy and open that ball valve. I bet your buddy gets a little upset with you for squirting him with oil. The pressure outside would be 0 psi and they will equalize. I will say that cars that use a low pressure rubber hose for a oil line tend to see the big drop in pressure at the gauge, cars with harder high pressure lines or smaller diameter lines don't see this drop as often or as much drop on the gauge. I believe it's because of the slower bleed off from the gauge allows the pressure to equalize faster.

quote:
Originally posted by wareagle87:
I may be way off here, but oil in an incompressible fluid. Therfore the pressure at the pump dischange will be felt at the gauge. Again, I am no physicist, but....


James Ott
Dirt Maniac

Total posts: 170
posted December 12, 2005 07:08 PM  
any fluid is compressable generally at 1/2% by volume. The squirt comes from the coiled brass tube inside the gauge. It trys to straighten itself out under pressure and then coils itself up when the pressure is relieved. Thats pretty much explains how the guage works. The coil is attached to a tiny rack and pinion. Anyway tee in a oil pressure sending switch at the pressure hole in the motor. Hook it up to a light. I saved a motor when it began to flash intermittantly. My driver may have missed this on a gauge, but he saw the light.

Normal Sullivan
Dirt Forum Racer

Total posts: 83
posted December 12, 2005 09:26 PM  
Correction: Most petroleum based oils are compressible by .05% at between 1000 and 4000 psi. Water is pretty much incompressible at any reasonable pressure. None of this comes into play at or near race-car oil pressure. Other than that, James Ott is right, when pressurized liquid sprays at you, (or your oil pressure gauge reads low) it's because of trapped air, or some moveable part of the gauge, not the oil being "squeezed".

awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 13, 2005 11:47 PM  
I wasn't trying to debate oil being compressed or not, if it did compress motors would NOT live. Enough said, my point was the pressure seen at the gauge will force oil backward in the system. Obviously it's not going to the oil pump.....but my point of the system oil seeing 30 psi and being a open system, with the gauge being a closed system that dead ends......the pressure needs to equalize....... the softer the hose, the bigger diameter the hose, and the longer the hose are all thing that expand under pressure and allow EXTRA volume of oil into the closed system (gauge) when the pressure going in is less than the pressure already there.......where does the volume go? back out into the oil system, so instead of see pressure going into the gauge you would see pressure going out.....

the only other thing I can think of is valve bounce.......spring always has pressure so if the valve isn't being lifted how can it BOUNCE OFF THE SEAT.....the old deal, for every action there is a re-action.

Normal Sullivan
Dirt Forum Racer

Total posts: 83
posted December 14, 2005 03:20 AM  
I was with you for a while, then you lost me. True that a soft, large diameter, long hose will contain a greater quantity of oil. I don't see how this could effect your oil pressure reading unless that line contained your entire oil capacity.
A sudden depressurization at the source (the oil pump) from 70, to say 20 psi would result in a decrease in the volume of oil contained in the line, and in the gauge itself, it wouldn't however cause the guage reading to drop below 20 psi. There's not enough volume or velocity involved to create a reversion effect, especially if the line is supple. So: yes, the oil trapped in your "closed system" would travel toward the pump by some amount, (which would be the precise volume of oil gauge capacity between a needle position of 70 psi and 20, plus any decrease in length/diameter of the feed line) No, it would not cause the gauge to reverse itself beyond the actual pressure loss.

I work in the hydraulics manufacturing industry. When a system is built to operate at extreme pressure differentials (0-3500 psi) and rigged with high pressure stainless steel hard lines, it's usually necessary to add an "accumulator" to the system in order to filter out pressure spikes. These accumulators consist of a steel container, divided by a rubber bladder, and pressurized on one side with nitrogen, the other side being exposed to system pressure. This is exactly the same effect as having a soft line in the system. This design (adding a slightly expandable section of hose) is often used in low volume systems to cancel the effect you're saying it causes. (also much cheaper than adding an accumulator)

[This message has been edited by Normal Sullivan (edited December 14, 2005).]

rrrrick
Dirt Freak

Total posts: 205
posted December 14, 2005 08:43 AM  
As insightful as all these answers on hydraulic principles are, could your track exit be uphill and to the right? When I race at the one of the tracks near me, the right turn up the banking always makes the oil light flash. Never any other racetrack, are you running a stock pan? Maybe the oil is running away from your pick-up when you hit the brakes to pull into the pits.

leapinlizard
Dirt Freak

Total posts: 430
posted December 14, 2005 09:07 AM  
That happens to me at my track as well. When you go outa turn four and up the steep banking to pack the track the oil light flashes to you get up some speed. I'm not the only one it happens to either.

awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 14, 2005 10:41 PM  
Normal, While I value and resecpt your knowledge and opinions, You are comparing a accumulator designed to filter out pressure spikes, not pressure drops. What does the gauge on your accumulator show? because that would be the gauge we are talking about. You seem to think, beleive or KNOW that your system cancels the effects I claiming it causes.......every spring has recoil, and I assume the gauge has a spring. we are talking about a gauge is the closed system, and it appears to me that what you say confirms what I stated, the rubber hose in a low volume system you stated acts as the accumulator cheaper???. You seem to be comparing the open end of a system to the closed end when talking about pressure spikes??? to compare apples to apples your closed system would need to drop from 3500psi to around 1000psi and stay there, tell me what happend to the pressure gauge in the accumulator?? it drop to a thousand and stayed there??? but you have nitrogen on one side to give you your pressure, and that is what maintains your constant pressure on your CLOSED system??

I'm not trying to argue or even debate this subject, your knowledge appears very high on this subject, I just don't believe I have anything backward on rubber hose canceling the effect I claim it causes, does the rubber hose act like a spring? so, would it not add MORE recoil to the system?

quote:
I work in the hydraulics manufacturing industry. When a system is built to operate at extreme pressure differentials (0-3500 psi) and rigged with high pressure stainless steel hard lines, it's usually necessary to add an "accumulator" to the system in order to filter out pressure spikes. These accumulators consist of a steel container, divided by a rubber bladder, and pressurized on one side with nitrogen, the other side being exposed to system pressure. This is exactly the same effect as having a soft line in the system. This design (adding a slightly expandable section of hose) is often used in low volume systems to cancel the effect you're saying it causes. (also much cheaper than adding an accumulator)

[This message has been edited by Normal Sullivan (edited December 14, 2005).][/B]



Normal Sullivan
Dirt Forum Racer

Total posts: 83
posted December 14, 2005 11:02 PM  
Awkwardjeff: Peace. Wasn't trying to lecture. My experience has been that any needle bounce at that low pressure will be near instantaneous. But I do not claim to be an expert on someone else's race car. I was simply trying to illustrate that in theory a two to three second reading below actual pressure would be unlikely. Re: your post dec 9th.

I was viewing the gauge/line as a closed portion of an open system, in that the reduction in oil pump output shouldn't result in zero pressure, or negative pressure at the gauge fitting, just a decrease in positive pressure by a defined amount.

[This message has been edited by Normal Sullivan (edited December 14, 2005).]

awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 15, 2005 10:38 AM  
Normal,

The following sentance of what you quoted on my Dec 9th post states... I'M NOT SAYING THIS IS GOING ON. So my thoughts weren't too strong. I tossed the idea out as food for thought.

The person that started this thread was 11dirt, and his question was why the pressure dropped at the gauge to 5-10 psi then returned to NORMAL.... he didn't post what normal pressure would be.... I assumed when racing it was between 60-70psi and at idle with hot oil after the race normal would be 20-30 psi. So to me the EXTRA drop of say 10 psi for a second or two, he never stated the gauge got to ZERO..... personally I don't believe too stronly in what you THINK I believe in.....

I will through this out there now for debate.....let's say you put your motor in and have a new gauge and a new line that neither has ever had oil inside them before, you hook the hose to the block and don't bleed the air. We all agree you have trapped air going to the gauge now, what if when you go from racing to idle the pressure inside the gauge forces air backward (to a small degree) into the oil system? the air bubble enters the system, at that instant there would be ZERO pressure going to the gauge??? do you agree??? While you have Zero pressure entering the gauge it drops below what NORMAL would be....say 30psi for hot idle.....but the gauge would recover to 30 psi before the reading at the gauge got to zero??
I would also add to this conversation that with liquid filled gauges the problem of pressure drop at the gauge seems to disapear when going from racing to hot idle. Why is that? because the gauge has a resistance and doesn't respond quickly, when you shut the motor off it takes 2 or 3 seconds for the gauge to bleed off to zero. With a standard gauge the gauge will read ZERO much quicker when you shut off the engine.
Again, I beleive it's trapped air causing this problem...... and I'll give credit to James Ott for bring that thought into the converastion first. But as I read his post he seem to have the same pressure drop and talked about using a smaller line next year. Because he brought up the air subject I assume he bleeds his line at the gauge to remove as much trapped air as he can already, so to me there has to be a little more going on than just trapped air.
Like I posted in my original post dated Dec 9th this subject seems to come up every year, and almost everyone seems to have the same reading at the gauge. Eveyone seems to agree this drop is normal.....although it's never normal for the gauge to read ZERO while the engine is running. Since you work in the field we are discussing, what are YOUR thoughts on pressure drop at the gauge with a quick recovery? You have stated why some ideas don't hold water, but haven't stated your thought on what is going on. I'm stating to think you hold a secrete and aren't sharing your knowledge with the rest of us to sollve our problems. Jammin is going to have to start have new members sign a waiver agree to share any and all information before joining......LOL Like I stated, you seem very knowledgable in this subject and I would appreciate your thought in the causes of pressure drop then quick recocery.

[This message has been edited by awkwardjeff (edited December 15, 2005).]

James Ott
Dirt Maniac

Total posts: 170
posted December 15, 2005 06:12 PM  
I work in the Steel Forging industry where we use different sources of pressure. Air, Steam, Hydraulic. Our 1250 Ton press uses 1600 HP of motor and runs at 6000 PSI. We have seen all kinds of strange things happen. Some are easy to explain some are not. I would think that these dipps in the pressure reading that we are trying to figure out are directly related to air trapped in the line to the gauge. Pressure pulsations also cause lopey readings but I doubt that would be the issue here. As far as tubing size My line of thought was that although the gauge is a dead end there is oil flow in and out of the guage as the Bourdon Tube arcs and straightens with pressure fluctuations. A small Diameter line will dampen this effect and result in a slower more stable reading. The bigger line size would likely react quicker to pressure changes but be slightly more jumpy. Bigger tubing also will hold alot more air. To sum all of this great debate up I would think you need a short as possible rigid material line (copper, stainless, aluminum,) bled of all air and a quality gauge. We have not even begun to discuss neat stuff like cavitation, effects of foaming, pressure surges caused by filters. Brings to mind the KISS rule... KEEP IT SIMPLE STUPID!

James Ott
Dirt Maniac

Total posts: 170
posted December 15, 2005 07:17 PM  
Oh yeah the Compressibility of Oil is Approximately 1/2 % by volume per 100 psi

Normal Sullivan
Dirt Forum Racer

Total posts: 83
posted December 15, 2005 11:58 PM  
Sometimes I have a great deal of difficulty in this medium. I guess I come across as being argumentative when that really isn't my intention. I'm sure that if you met me in person you'd realize that I'm really just a total prick. Anyway, on to what I think might be causing 11dirt's oil pressure issue: As rrrrick alluded to, everything we do, oiling system wise, is intended to increase oil delivery under acceleration, turning left. If he's turning right to exit the track, under braking conditions, and following a period of high rpm engine operation, (which as you well know tends to force a significant portion of your oil supply into the upper engine, valve covers, etc.); my theory is that his oil pump is cavitating, thus causing a temporary decrease in his actual oil pressure as is indicated on the gauge. I also believe that as the dynamics of vehicle motion cease, and the oil makes it's return to the pan, the problem resolves itself.

A way to test this theory against the theoretical gauge inaccuracy/air bubbles argument is pretty simple: On your next test&tune day after completing a couple of laps at high rpm, just stop. if your oil pressure behaves as before, then it might be air bubbles, or reversion. If it doesn't, (and your oil feed line isn't wrapped around your steering shaft) then it must be something else.

Special note to James Ott: Horse 5hit.
Oil is not 100% compressible at 20,000 psi. The PV you've looked up is part of an equation used to calculate compressibility, not the compressibility itself. The part you're missing looks something like this:

co = -(1/V)(V/p)T
co = -(1/Bo)(Bo/p)T
co = (1/ro)(ro/p)T

Where co = isothermal compressibility psi-1
ro = oil density lb/ft3
Bo = oil formation volume factor, bbl/STB

In reality that's a non-linear compressibility of around 0.5% per 1000 psi in normal working conditions(<4000 psi), and is shown to increase with both temperature and pressure increases.

Finally as someone who works with hydraulics, steam, etc. You know rule 1: ALWAYS TRUST YOUR GAUGES

[This message has been edited by Normal Sullivan (edited December 15, 2005).]

[This message has been edited by Normal Sullivan (edited December 16, 2005).]

ford5
Dirt Forum Champ
Total posts: 728
posted December 16, 2005 05:30 AM  
Someone has tooooooo much time on their hands?
I think STYX had a song about this?

Normal Sullivan
Dirt Forum Racer

Total posts: 83
posted December 16, 2005 06:40 AM  
It appears that you dooooooo have time to stalk me through this forum, don'tcha, Asshelmet?


"STYX" Now That's funny!

awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 16, 2005 08:32 AM  
Normal,

I don't think you came across as argumentive to me or with me..... Like I stated you seemed to have more and better knowledge on this subject than your average racer. That is the reason I requested your thoughts, NOT so I could try and tear your thoughts to shreads.......
I totally understand your frustrations of trying to help people, there are many knowledgable people on this forum and we are all never going to agree on any one single thing. I would agree with your thoughts on this matter if everyone caused this problem while turning right to exit the track. To keep my gauge bounce to a minimum I went with a #3 steel braided line, most people use a #4 with a push on rubber hose, I also went to a liquid filled gauge, and bleed the air at the gauge every time we put a new motor in the car...I no longer have this problem. My gauge bounce occured when ever I went from racing to idle, when shifting into nuetral.....it didn't seem to matter on level ground, turning, stopping or anything else. after a race sitting still you could rev the motor to get 70psi then slam the throttle shut and the oil gauge would drop to around 20 then recover to around 25-30psi. I assumed everyone else tried these things before seeking help here in this forum.....although I could be wrong, nobody ever seemed to post if they tried these things to eliminate the thought of getting air in the oil system because of up hill right turn...... I've only once had a oil related bearing problem, and I know what the problem was there......knocked a hole in the oil pan with 2 laps to go while racing for the WIN......LOL, engine slowed down and I finished 2nd, oil light didn't come on until 1/2 lap to go..... While we don't all agree we should be willing to explore each others idea and thoughts, while still being respectful. Thanks for your input on this subject.

[This message has been edited by awkwardjeff (edited December 16, 2005).]

James Ott
Dirt Maniac

Total posts: 170
posted December 16, 2005 05:18 PM  
Holy Sullivan PHd. Take it easy lemon squeezy!!!! Man these guys are not into alot of formula's and brew haha, they want answers that will help them fix something or understand why it can't be fixed. How does the density of oil per cubic foot come into play? I could give a rat'sass!!

Cavatation will cause wild gauge readings as the vacuum bubbles form and then implode. Cold oil will not readily flow as easy through the pump pick up at 7000 rpm as hot oil. As well as air entrainment caused by windage problems will cause crazy readings. I'm not buying stuffing 6 quarts of oil into one valve cover. Crank windage I will definately buy. Anyway here's a thought: Does a blip in the oil pressure guage that last for a half a second mean anything? Probably not. If your oil pressure at idle is say 15-20 PSI after a 30 lapper I would think that is OK as long as when it is revved you get an increase of oil pressure. Oil viscosity will be real thin and the clearances will be wide open and since pressure is derived from a resistance to flow, thin oil and hot clearances greatly reduces the resistance to flow therefore the pressure would be expected to be lower. This would be the case especially at idle when pump volume is low.

Normal Sullivan
Dirt Forum Racer

Total posts: 83
posted December 16, 2005 07:53 PM  
James, Friend, I'm not attempting to argue against anyones opinion. I've offered mine, and I've attempted to explain the reasons I hold such an opinion. My difference with your previous statement reguarding oil compressibility, isn't one of "opinion" it's a matter of physics. The "formula" was for your benefit not everyone else's. Sorry it showed up all messed up.

That being said, every other post I've made in this thread came with a qualifier such as: "theory" "My opinion" "I do not claim to be an expert on someone else's race car", etc.

Returning to the original post in this thread, I still hold the opinion I stated here Dec 15th. His problem is probably related to sucking air at the oil pump, based on what he wrote in his post.

Whether or not air entrainment, reversion, pressure fluctuations, bourdon-tube pressure, or feed line diameter/resilience might cause a fluctuation in guage reading with no other contributing factor makes for an interesting academic discussion, but really.....None of this is personal to me. I don't think, based on what I know about fluid dynamics, that this is the case, but I have no vested interest in disproving it either. I'm just joining the conversation.

Finally, Please overlook ford5, I once failed to worship his trophys, and he's not over it yet

[This message has been edited by Normal Sullivan (edited December 16, 2005).]

awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 16, 2005 10:04 PM  
I do know this much about ford5, he doesn't have one trophy......... he and I break the plastic tops off and use them for door stops, the wooden base is tossed in the shop stove to offset the cost of heating the race shop to afford more speed parts.

Normal Sullivan
Dirt Forum Racer

Total posts: 83
posted December 16, 2005 10:41 PM  
That's nice.

ford5
Dirt Forum Champ
Total posts: 728
posted December 17, 2005 03:03 PM  
Keep tryin' there Ole Abby Normal....maybe you will win one someday?

ford5
Dirt Forum Champ
Total posts: 728
posted December 17, 2005 03:07 PM  
Hey, Jeff long time no see! You have a good season? Are you still building cars? Have a Merry Christmas and Happy New Year.

awkwardjeff
Dirt Forum Champ
Total posts: 589
posted December 17, 2005 08:29 PM  
hey ford5,
Season was okay ....won some, wrecked some, but didn't break much. It sounds like you made many NEW friends in my absents.....LOL

I would like to wish everyone a happy holiday season, including BOTH you and normal and my ole buddy SNOWMAN where ever he may be these days. My wife has a Christmas card sitting on the kitchen table waiting for me to get his NEW address. So SNOWMAN.........PM your new address to me, or email.........or stay home and answer your phone.....LOL

Normal Sullivan
Dirt Forum Racer

Total posts: 83
posted December 17, 2005 10:01 PM  
Thanks Jeff,

Merry Christmas and a blessed and happy new year to everyone here at The Dirt Forum, all of your families, and all of your crew. (That means you too Asshelmet)

Normal Ray Sullivan

James Ott
Dirt Maniac

Total posts: 170
posted December 18, 2005 09:53 AM  
Yeah but we run nothing but AMSOIL in all of our stuff.

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