Why Does The Oil Pressure Gauge Bounce?
02-27-2008, 01:33 PM
#31
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What does that mine for none technical people?
I have seen guages bounce like crazy and mine does that aswell and after every fill up my guage only shows 3/4 full! I've talked to my mechanic and he said that the reason is bad wiring! After 20 some years the wiring is frail and to weak to supply proper power! Alot of other people said after installing a new battery cable from Ice Shark or other similar products on there porsche's mostly all problems went away and the car felt a little better by running smoother and starting up right away and no hesitations.
So I am doing a full Ice Shark wiring kit including the headlights! I checked all my other connections to no luck and found some of my wiring is just crap and very skinny and in no way able to supply proper power! And Porsche designers should of addresed this issue!
02-27-2008, 09:35 PM
#32
Rennlist Member
Here's the best analogy I can come up with.
Have you ever put your thumb over the end of a garden hose to squirt some water? Well, your thumb is like the oil pressure relief valve (OPRV). And the garden hose is like the oil pump. If someone asks you to squirt a stream of water 10 feet away, you pretty quickly find the right pressure to apply to the hose. Now if someone turns the spigot to reduce the water flow (this is like the engine reducing rpms and going to idle), you apply more pressure to maintain the 10 foot stream.
Ok, so I bet you're asking, "Well why doesn't the stream of water bounce like on my car?" That's because you're smart and have eyes. You can see the stream and you have feeling in your thumb, so you know how to make the necessary adjustments to maintain the 10 foot stream. The OPRV is just a dumb spring. It can't see what's going on and has no feeling. It applies the same pressure all the time. When the flow is low like at idle, the OPRV partially covers the orifice that sends oil to the rest of the engine. This eventually builds enough pressure to compress the spring and move back the OPRV to uncover more of the orifice. This sends more oil to the engine and the gauge jumps up to a higher reading. There's not enough flow to hold the OPRV back, so it closes again, and the oil pressure goes down. And the cycle repeats. This is the oscillation or resonance you see. This is why you only see this at idle and when the oil is up to temp. Other times there is enough flow and viscosity to maintain the pressure.
The gauge isn't damped, which means you see what is actually happening. It is the same for the water temperature gauge. You can see it rise going up steep hills, and see it go down when you go down a hill. Most people don't like all this moving around and it scares them. "Oh my God! The temps going up! It's over heating when I go up hills!" So to reduce calls to the dealership, the car manufacturers make their gauges slow reacting so you don't see the little jumps. All you see is a steady needle. I can only surmise that the newer oil pressure sender units have an internal damping capacitor to stop the bouncing.
I personally like seeing what's really happening, and I'm glad my 944 gives it to me. Unfortunately, the masses think otherwise, so we get these dumbed down gauges. BTW It's not the grounds!
Hope that helps.
Have you ever put your thumb over the end of a garden hose to squirt some water? Well, your thumb is like the oil pressure relief valve (OPRV). And the garden hose is like the oil pump. If someone asks you to squirt a stream of water 10 feet away, you pretty quickly find the right pressure to apply to the hose. Now if someone turns the spigot to reduce the water flow (this is like the engine reducing rpms and going to idle), you apply more pressure to maintain the 10 foot stream.
Ok, so I bet you're asking, "Well why doesn't the stream of water bounce like on my car?" That's because you're smart and have eyes. You can see the stream and you have feeling in your thumb, so you know how to make the necessary adjustments to maintain the 10 foot stream. The OPRV is just a dumb spring. It can't see what's going on and has no feeling. It applies the same pressure all the time. When the flow is low like at idle, the OPRV partially covers the orifice that sends oil to the rest of the engine. This eventually builds enough pressure to compress the spring and move back the OPRV to uncover more of the orifice. This sends more oil to the engine and the gauge jumps up to a higher reading. There's not enough flow to hold the OPRV back, so it closes again, and the oil pressure goes down. And the cycle repeats. This is the oscillation or resonance you see. This is why you only see this at idle and when the oil is up to temp. Other times there is enough flow and viscosity to maintain the pressure.
The gauge isn't damped, which means you see what is actually happening. It is the same for the water temperature gauge. You can see it rise going up steep hills, and see it go down when you go down a hill. Most people don't like all this moving around and it scares them. "Oh my God! The temps going up! It's over heating when I go up hills!" So to reduce calls to the dealership, the car manufacturers make their gauges slow reacting so you don't see the little jumps. All you see is a steady needle. I can only surmise that the newer oil pressure sender units have an internal damping capacitor to stop the bouncing.
I personally like seeing what's really happening, and I'm glad my 944 gives it to me. Unfortunately, the masses think otherwise, so we get these dumbed down gauges. BTW It's not the grounds!
Hope that helps.
02-27-2008, 10:45 PM
#33
Not Special
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Great analogy, StoogeMoe!
So, here's a separate question...when I put my clutch in, the oil pressure gauge dives down (sometimes to 1) before going back up to 2/2.5/3. That also have to do with the OPRV?
So, here's a separate question...when I put my clutch in, the oil pressure gauge dives down (sometimes to 1) before going back up to 2/2.5/3. That also have to do with the OPRV?
02-27-2008, 11:07 PM
#34
Rennlist Member
I'm not an electrical expert but maybe some motivated individual (read: not me) could try the following: disconnect the sender leads and measure the resistance while the engine is running. Do the ohms still bounce? This would rule out anything beyond the sender such as the cluster gauge or wiring. Another test: figure out which wire is ground then run an auxiliary ground wire to the block from the sender. Fix the problem? My last idea involves someone who had the bounce going on, then added an aftermarket oil pressure gauge which included replacing the OEM sending unit. No bounce on the aftermarket gauge would rule out mechanical problem such as the precursor to rod bearing failure.
02-28-2008, 12:27 AM
#35
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Normal if it wiggles a bit between certain oil pressure (i see 2.5-3.0bar on idle fully warm on 20w50).
New sending unite, new oil cooler seals and still no difference. I do recall that the oil pressure was more 'stable" and a tad higher after i replaced the front engine seals (including the oil pump seals).
PS: My 88 NA did the exact same thing, if it wiggles or 'bounces' violently, then i would say it is not normal, a bit is fine.
New sending unite, new oil cooler seals and still no difference. I do recall that the oil pressure was more 'stable" and a tad higher after i replaced the front engine seals (including the oil pump seals).
PS: My 88 NA did the exact same thing, if it wiggles or 'bounces' violently, then i would say it is not normal, a bit is fine.
02-28-2008, 12:38 AM
#36
RL Community Team
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I have to disagree with Stoogemoe's comment. It makes sense but I don't think that's what is happening in this case. Why do I say this? Both my 968s have steady guages. I have seen plenty of 944s with steady gauges too. If it was a result of spring oscillation, then all cars would have this problem, not just some.
Lizard brings up an excellent point I was just about to make. Measuring the signal directly at the sender, and sending a dummy signal to the gauge, would be good places to start in troubleshooting. I have a feeling the problem isn't in the gauge, wiring or sender.
Lizard brings up an excellent point I was just about to make. Measuring the signal directly at the sender, and sending a dummy signal to the gauge, would be good places to start in troubleshooting. I have a feeling the problem isn't in the gauge, wiring or sender.
06-07-2012, 12:18 PM
#37
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This seems like a good theory but maybe you can help explain this. Since new my 951 has never had a bouncing oil pressure gauge. It moves quickly sometimes but never continuously bouncing.
I had my cylinder head done, new belts and head gasket. Now my oil pressure gauge is bouncing +/- 2 bar while idling hot. Constantly bouncing...
I can't help but think there is an issue. It's never done this before.
I had my cylinder head done, new belts and head gasket. Now my oil pressure gauge is bouncing +/- 2 bar while idling hot. Constantly bouncing...
I can't help but think there is an issue. It's never done this before.
Here's the best analogy I can come up with.
Have you ever put your thumb over the end of a garden hose to squirt some water? Well, your thumb is like the oil pressure relief valve (OPRV). And the garden hose is like the oil pump. If someone asks you to squirt a stream of water 10 feet away, you pretty quickly find the right pressure to apply to the hose. Now if someone turns the spigot to reduce the water flow (this is like the engine reducing rpms and going to idle), you apply more pressure to maintain the 10 foot stream.
Ok, so I bet you're asking, "Well why doesn't the stream of water bounce like on my car?" That's because you're smart and have eyes. You can see the stream and you have feeling in your thumb, so you know how to make the necessary adjustments to maintain the 10 foot stream. The OPRV is just a dumb spring. It can't see what's going on and has no feeling. It applies the same pressure all the time. When the flow is low like at idle, the OPRV partially covers the orifice that sends oil to the rest of the engine. This eventually builds enough pressure to compress the spring and move back the OPRV to uncover more of the orifice. This sends more oil to the engine and the gauge jumps up to a higher reading. There's not enough flow to hold the OPRV back, so it closes again, and the oil pressure goes down. And the cycle repeats. This is the oscillation or resonance you see. This is why you only see this at idle and when the oil is up to temp. Other times there is enough flow and viscosity to maintain the pressure.
The gauge isn't damped, which means you see what is actually happening. It is the same for the water temperature gauge. You can see it rise going up steep hills, and see it go down when you go down a hill. Most people don't like all this moving around and it scares them. "Oh my God! The temps going up! It's over heating when I go up hills!" So to reduce calls to the dealership, the car manufacturers make their gauges slow reacting so you don't see the little jumps. All you see is a steady needle. I can only surmise that the newer oil pressure sender units have an internal damping capacitor to stop the bouncing.
I personally like seeing what's really happening, and I'm glad my 944 gives it to me. Unfortunately, the masses think otherwise, so we get these dumbed down gauges. BTW It's not the grounds!
Hope that helps.
Have you ever put your thumb over the end of a garden hose to squirt some water? Well, your thumb is like the oil pressure relief valve (OPRV). And the garden hose is like the oil pump. If someone asks you to squirt a stream of water 10 feet away, you pretty quickly find the right pressure to apply to the hose. Now if someone turns the spigot to reduce the water flow (this is like the engine reducing rpms and going to idle), you apply more pressure to maintain the 10 foot stream.
Ok, so I bet you're asking, "Well why doesn't the stream of water bounce like on my car?" That's because you're smart and have eyes. You can see the stream and you have feeling in your thumb, so you know how to make the necessary adjustments to maintain the 10 foot stream. The OPRV is just a dumb spring. It can't see what's going on and has no feeling. It applies the same pressure all the time. When the flow is low like at idle, the OPRV partially covers the orifice that sends oil to the rest of the engine. This eventually builds enough pressure to compress the spring and move back the OPRV to uncover more of the orifice. This sends more oil to the engine and the gauge jumps up to a higher reading. There's not enough flow to hold the OPRV back, so it closes again, and the oil pressure goes down. And the cycle repeats. This is the oscillation or resonance you see. This is why you only see this at idle and when the oil is up to temp. Other times there is enough flow and viscosity to maintain the pressure.
The gauge isn't damped, which means you see what is actually happening. It is the same for the water temperature gauge. You can see it rise going up steep hills, and see it go down when you go down a hill. Most people don't like all this moving around and it scares them. "Oh my God! The temps going up! It's over heating when I go up hills!" So to reduce calls to the dealership, the car manufacturers make their gauges slow reacting so you don't see the little jumps. All you see is a steady needle. I can only surmise that the newer oil pressure sender units have an internal damping capacitor to stop the bouncing.
I personally like seeing what's really happening, and I'm glad my 944 gives it to me. Unfortunately, the masses think otherwise, so we get these dumbed down gauges. BTW It's not the grounds!
Hope that helps.
06-07-2012, 12:54 PM
#38
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perhaps you never got the memo....
it's a 2.5 litre lawnmower engine.
nothing fancy. nothing exotic. nothing special here.
it's just a bigger Audi engine from the early 1970s. ok we've all heard it's half a 928 engine.
but however way you prefer to think about it, all 4 cylinder engines are a compromise.
and all your oil-starved, 25-year-old motors are gonna run pretty rough.
on mine, sometimes there's a slight bounce when i let off the gas....
and it's only an 18-year-old, ****box 4 cylinder.
one weird thing ? i haven't had any noisy, oil-starved lifters ticking in over a year.
must be doing something wrong.
it's a 2.5 litre lawnmower engine.
nothing fancy. nothing exotic. nothing special here.
it's just a bigger Audi engine from the early 1970s. ok we've all heard it's half a 928 engine.
but however way you prefer to think about it, all 4 cylinder engines are a compromise.
and all your oil-starved, 25-year-old motors are gonna run pretty rough.
on mine, sometimes there's a slight bounce when i let off the gas....
and it's only an 18-year-old, ****box 4 cylinder.
one weird thing ? i haven't had any noisy, oil-starved lifters ticking in over a year.
must be doing something wrong.
06-07-2012, 05:32 PM
#39
Race Car
Here's a suggestion that fixed my bouncy gauge, especially the gauges that bounce rythmically every couple of seconds.
Go to the back of the car and clean the fuel tank sender connections and tighten the fuel sender bolts untill they are snug. Poor connection at my fuel sender fixed my problem.
Does anyones fuel gauge bounce around a bunch also when this is happening?
Go to the back of the car and clean the fuel tank sender connections and tighten the fuel sender bolts untill they are snug. Poor connection at my fuel sender fixed my problem.
Does anyones fuel gauge bounce around a bunch also when this is happening?
06-08-2012, 10:15 AM
#41
Proprietoristicly Refined
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I installed a spare OPRV with 2 new "O" rings a few days ago in the '87 and the bounce diminished.
Idle oil pressure reading improved .
High rpm still only reads 4+.on the '87. The '88 is always a solid 5~.
Using Castrol GTX 20-50. to full mark, Mahle filter. PHX temps over 100*
Watching the oil pressure to see when I need to replace the rod bearings on the '87.
John
Idle oil pressure reading improved .
High rpm still only reads 4+.on the '87. The '88 is always a solid 5~.
Using Castrol GTX 20-50. to full mark, Mahle filter. PHX temps over 100*
Watching the oil pressure to see when I need to replace the rod bearings on the '87.
John
06-09-2012, 10:30 AM
#43
Nordschleife Master
I'm almost certain that this bouncing is nothing to do with the oil presure switch, rod bearings or OPVR. It's to do with the instrument gauge. All analog gauges have a damper spring/mechanism that weakens over time, it stops the needle from overshooting a reading. The oil pressure measuring system in our cars is driven my two oscillating parts, the OPVR and the sensor. These combined cause a lot of strain on the guage damper all of the time and it weakens. The weakening of the damper causes the guage needle to bounce more as it gets older which in turn causes the damper to wear more.
A while ago I fitted the almost stable instrument cluster from one of my cars to the one that bounced a lot and it didn't bounce anymore. I'm therefore convinced the only permanent cure is a new oil pressure guage.
A while ago I fitted the almost stable instrument cluster from one of my cars to the one that bounced a lot and it didn't bounce anymore. I'm therefore convinced the only permanent cure is a new oil pressure guage.
06-09-2012, 01:03 PM
#44
Race Car
My 87 (924S) has new rod bearings and the same was still happenning until I cleaned the fuel sender conections. I do still have the old style OPRV, but I have never seen oil pressure below 3.0 even at 100+ degree temps with the AC blasting(20/50 Amsoil). I chased the issue with different senders(3 total) and it never made a difference. Keep in mind that the 924S has the old style gauges and wiring and that may possibly factor into my results. My oil pressure is rock steady now.
If one were to attach an ohm meter directly to the sender you may not get the best results unless it is an analog meter. A digital ohmmeter will not sweep fast enough to tell the tale.
If one were to attach an ohm meter directly to the sender you may not get the best results unless it is an analog meter. A digital ohmmeter will not sweep fast enough to tell the tale.
06-09-2012, 09:13 PM
#45
Proprietoristicly Refined
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Repeating a picture I just posted but it applies here as well.
From sponsor 944Online:
This morning I did replace my oil pressure sender with a very HD "Italian" oil pressure sender I had on the shelf. You can tell by the picture it is taller and weighs twice the Porsche/German OEM on the left. The gauge is a standard 0-5 bar that fits.
The '87 924S oil pressure at cold startup is now ~5 bar and hot engine, 100* temps,
the presure now stays above 4 to 4.5 bar driving speeds at hot engine temp.
The gauge flicker has also diminished but whalebird may be correct on the "old style gauges and wiring" for a final fix.
Repeating what 944Online says, "URO oil pressure senders are CRAP"
John
From sponsor 944Online:
This morning I did replace my oil pressure sender with a very HD "Italian" oil pressure sender I had on the shelf. You can tell by the picture it is taller and weighs twice the Porsche/German OEM on the left. The gauge is a standard 0-5 bar that fits.
The '87 924S oil pressure at cold startup is now ~5 bar and hot engine, 100* temps,
the presure now stays above 4 to 4.5 bar driving speeds at hot engine temp.
The gauge flicker has also diminished but whalebird may be correct on the "old style gauges and wiring" for a final fix.
Repeating what 944Online says, "URO oil pressure senders are CRAP"
John
