PDA

View Full Version : OT: Is my oil pressure gauge an idiot light in disguise?



winchman
07-21-2009, 01:45 AM
I've got a 2000 Silverado with the 4.8L engine. The oil pressure has always read just under 60psi whenever the engine is running. It DOES move about a needle width up or down in response to changes in engine temperature and speed.

I noticed quite a bit of oil pressure variation on the other cars I've driven recently that had gauges. Most would be around 30psi at idle, and go up to 60+psi at highway speeds. They'd read higher when the engine was cold.

Why would the Silverado have such consistent oil pressure when other engines vary all over the gauge as conditions change? The small changes I see suggest it's really reading pressure, but is it really an idiot light in disguise?

Roger

dp
07-21-2009, 02:22 AM
I've got a 2000 Silverado with the 4.8L engine. The oil pressure has always read just under 60psi whenever the engine is running. It DOES move about a needle width up or down in response to changes in engine temperature and speed.

I noticed quite a bit of oil pressure variation on the other cars I've driven recently that had gauges. Most would be around 30psi at idle, and go up to 60+psi at highway speeds. They'd read higher when the engine was cold.

Why would the Silverado have such consistent oil pressure when other engines vary all over the gauge as conditions change? The small changes I see suggest it's really reading pressure, but is it really an idiot light in disguise?

Roger

Check it again in 10 years. It will read lower.

darryl
07-21-2009, 02:44 AM
Just a guess, but maybe if the engine is tight not too much oil is bypassed through play in bushings, etc. In that case the regulator on the oil pump may be operating in a better range. When more oil passes through the engine parts, the regulatir won't be bypassing as much oil internally so it probably allows more variation in oil pressure. The gauge, if it's working properly, will show this. I don't know if the gauges themselves go bad, but maybe they do contribute to the changes in readings.

I suppose it's possible that a particular engine would have a higher volume oil pump by design to ensure that even when the oil is hot, the engine is worn, or is run at low speeds, there will always be a reserve oil pumping capacity to keep the engine fully lubed. In this case, most of the oil pumped would be bypassed around the pump, and the minimum amount the engine is using doesn't represent much of a change to the oil pressure regulator. In this case the gauge wouldn't fluctuate much at all.

Just a few thoughts.

Evan
07-21-2009, 05:21 AM
A quick check of the automotive forums suggests that problems with the oil pressure sensor are common. The gauge will either read high all the time or will drop to zero when the engine warms up.

Doc Nickel
07-21-2009, 07:05 AM
Modern gauge clusters are, indeed, little more than glorified idiot lights.

The fuel-level gauge, for example, has been 'dampened' almost since it's inception. If it read direct, the needle would sway erratically due to the fuel sloshing in the tank. So the gauge is "damped" to the point it takes many seconds for the needle to react to a level change.

More recently, they've added- or increased- the damping to the others as well, the oil pressure especially. People would see the gauge read high when cold, then drop alarmingly when the engine warmed up, and then vary considerably as the engine speed or load changed. They'd bring the car back to the dealer and complain of varying oil pressure, and demand it be "fixed".

Ditto the water temperature- the average motorist, assuming he or she pays any attention to the gauges at all, wants to see that needle in the same place, each day, all day, every day. Doesn't matter whether it's 104 in the shade or twenty below- if the needle's not where the owner thinks it should be, he runs it back to the dealer and demands they fix it.

People have written whole books on the subject. Literally. :D

So today, generally, the only gauges the motorist really pays attention to are the gas gauge and the speedo- most often in that order.

All the other gauges are simply idiot lights with a needle- the needle is designed to point to the middle of the range unless the value falls below a set point, at which time the needle moves considerably, in order to attract attention.

If you want true direct-reading gauges, you'll have to install an aftermarket set- and preferably mechanical ones. I'll bet if you do so, your "60 psi" will turn out to be about 30, probably dropping to the high teens, low twenties at idle.

Doc.

Dawai
07-21-2009, 07:33 AM
http://photos-e.ak.fbcdn.net/hphotos-ak-snc1/hs125.snc1/5380_1083944100994_1298124187_30198500_685146_n.jp g
What I put in my old el Camino when the idiot light "switch" died. I was afraid to drive it for a few days till I could get this mechanical guage in. I still have to hook the probe up in the head there on the left, drain some coolant, install.

Some vehicles the gauges are tied to the computer, the actual sensor tied to the computer also.. I remember something doing the gauge bang-biff-bang as a indicator for "something"?? perhaps it was the old Ford Taurus we had for a while?? It also had the ac compressor and other things computer controlled.

(mine is running 60 at idle.. does not increase with rpm, the spring-bleed off is right there, new engine with less than 100 miles) No idea what kind of pump this engine has in it. I have not even been able to paint it from Raw clean metal yet..

I can remember while building the engine for the old tattoo bus, (I was drinking) I not only knocked out the carter key, but put a washer and stretched the bypass spring on the pump. When I cranked it, it pegged at 100psi, the oil filter split down the side.. I thought it was blowed for a moment.. I had to run a special "thick" wall oil filter made for stock cars ($32.50) I got snookered out of my bus by a band group-preacher with a promise, trusting devil that I am.. I didn't even look under his trader van.. it had the motor "chained in" sitting on 2x4 blocks to secure the broken motor mounts..

Later I remember seeing the mini bus with a oil "path" in behind it. Never saw it on the road again.. I had forgotten to tell him about he special oil filter it required.

A.K. Boomer
07-21-2009, 08:23 AM
Winchman, Do you have a manual transmission?
If so load the engine down to about 600 rpm's and check the results when warm, You should see a difference at this rpm, You just might have some very good news, you might have an engine that's holding pressure very well,
On the old volkswagons with the idiot lights it's a way me and my bro used to rough guess the engines internals --- first check them cold by shutting off the engine and then just turning the ign. switch back on and count the seconds till the light appears, then with a warm engine we would load the engine below idle, some would have a flickering light - some would remain off, When you had a warm engine that you would have to turn off and then turn the switch back on and count to 3 seconds you were fairly sure you had a tight one (rods and mains cam bearings lifters and oil pump)
This was a good test in one direction as its tough to be fooled by a sender unit with zero pressure otherwise it would remain off all the time --- but on the flip side, the engines that would flash early were not a guarantee to be worn out, Many senders had way to high of a rating and triggered early, we had a test sender we knew was good and would swap it out -- if the light triggered early after that we knew we had what we called a "bleeder"...

Gauges are tougher due to the time delay but there are methods -- If you have an automatic trans and cant load the engine then just pull the ECU fuse and crank without starting -- this is low enough speed that with a warm engine you should get the proof you need that your gauge is indeed covering the range and not just some kind of needle that's getting hung up in the middle...

Carld
07-21-2009, 08:25 AM
I don't know about Chevy but Ford Rangers that have an oil pressure gauge have an oil pressure SWITCH that an idiot light would use rather than an oil pressure sender. There is a resistor across the terminals on the back of the gauge to make the gauge read the same thing all the time. Ford did it because of oil pressure complaints of low oil pressure at idle. You can fix it by replacing the switch sender with a pressure sender and cutting the resistor out but you have to remove the instrument panel and not many are willing to do that. I'm sure Ford does the same on the rest of their models of cars.

Maybe Chevy does the same thing now. If the gauge is reading real oil pressure the gauge should show a pressure swing, not stay in one place.

Thanks to the idiots in the world we have idiot gauges. Manufacturers want to make the customers happy.

J Tiers
07-21-2009, 08:48 AM
I think you have a legitimate problem.

I have a 2000 S10, and the oil pressure gage does the normal 35 at idle, 60 at speed thing that you'd expect. The temperature gage and the voltmeter also do what would be expected.

Evidently, despite the gloom and doom crew here, the 2000 model year Chevy still had legitimate gages, at least on some models.

BTW, I don't have any clue why it would be a BAD thing for the gas gage to be 'damped" so that it does not hiccup and bounce every time you drive over a piece of parakeet poop. It is much more useful when it reads the average than if it swings wildly from full to empty. Otherwise you ahve to guess what the real reading is. I remember those days, when you had to do a "visual average" to arrive at the reading.....

NiftyNev
07-21-2009, 09:04 AM
- the needle is designed to point to the middle of the range unless the value falls below a set point, at which time the needle moves considerably, in order to attract attention.

In the case of some Toyota cooling system gauges they sit just below half way on the gauge through a wide range of hotter temperatures and then move suddenly if the engine overheats. By that time it's too late and the engine is cooked. This is why a low coolant alarm is a good thing to install. Early warning of coolant loss long before the gauge moves.

Nev

Evan
07-21-2009, 09:24 AM
The gauge on the Silverado is supposed to read like a regular oil pressure gauge. It isn't an "idiot gauge". The problem is most likely the sensor since that matches the description of many similar problems on a variety of forums.

aboard_epsilon
07-21-2009, 09:43 AM
bad thing ..
my fuel gauge reads/ remembers/ stays there ....even with the batt disconnected .

so all the fuel thief would have to do is have a look at your dials to see if you had a full tank............same with the thief who wants to steal the car...like this in all rovers made after a certain date.

all the best.markj

Evan
07-21-2009, 10:26 AM
So put a switch across the sender and leave the sender open/shorted (which ever suits) except when you need to read the fuel level.

Paul Alciatore
07-21-2009, 10:59 AM
I had a problem with an 84 Chevy truck. The dealer, no less, changed the sender for about $35. That was some years ago, but even at today's prices, I would imagine you could do it yourself for under $30, a good mechanic for under $50, or a dealer for under $75. It's an easy job on most engines - a lot like changing a spark plug.

If the gauge is reading when running and returns to zero when off (it moves across 1/3 to 1/2 of the scale), then the gauge itself is probably OK. If the wiring was bad, it would either not work or jump all over the place. Could be a computer/electronic problem, but senders are a lot cheaper so I would try that first.

Just replace the sender and see what happens.

aboard_epsilon
07-21-2009, 11:03 AM
So put a switch across the sender and leave the sender open/shorted (which ever suits) except when you need to read the fuel level.

Ive only got two gallons in the tank most of the time ..'cause I'm on LPG ..so don't matter much to me ...

all the best.markj

saltmine
07-21-2009, 11:09 AM
One thing everybody seems to forget is the fact that the "new generation" Chevrolet engines use a direct drive, variable displacement oil pump, instead of the old gearotor pump driven off of the distributor gear. Being a positive displacement pump, it delivers a very accurate ammount of pressure all of the time. I have a similar pump on my car, and even after 100,000miles it still registers 65psi on a mechanical gage.

saltmine
07-21-2009, 11:15 AM
Carl is right about the Fords. After a bunch of complaints about low oil pressure and erratic gage readings, Ford changed their gages to reflect a "fixed value" regardless of what the engine was doing. The oil pressure sender was nothing but an "NO/OFF" switch and the gage read the fixed value it was "programmed" with.
GM gages aren't very accurate, that's why they're called gages....if they were accurate, they'd be "instruments".
Basically, most dash gages are there to give you an idea of what's going on under the hood...and that's about all.
Don't worry, though. Chevrolet engines have been known to run happily on as little as 15psi of oil pressure.

Ridgerunner
07-21-2009, 11:34 AM
Many years ago my uncle worked as a mechanic in a Ford garage. A couple bought a new car and came back complaining about the fuel mileage. The dealer tried tuning it but the couple still complained. The dealer had my uncle change the odometer gear which solved the problem. :rolleyes:

A.K. Boomer
07-21-2009, 11:55 AM
Carl is right about the Fords. After a bunch of complaints about low oil pressure and erratic gage readings, Ford changed their gages to reflect a "fixed value" regardless of what the engine was doing. The oil pressure sender was nothing but an "NO/OFF" switch and the gage read the fixed value it was "programmed" with.



That's just plain crazy, in that case Id much rather have an idiot light as its just as accurate as the "gauge" and more apt to get your attention, might as well throw in a buzzer too... unbelievable.

fasto
07-21-2009, 12:23 PM
Should drive a German car...
My VW, oil pressure gauge actually reads oil pressure: 150 PSI winter cold starts, 30-50 PSI highway driving, ~0 PSI hot summer idle.
2 stage oil pressure idiot light: @ > 1500 RPM if < 15 PSI light on + buzzer, otherwise if < 3 PSI light on + buzzer.
Oil temp: reads out in 1 deg F increments, digital which I don't really like.
Water temp: 120 to 250 F, runs 160F in the winter & 200+ in the summer, changes with outside temperature!
Water temp idiot light: > 250F or so, light flashes.

Perhaps even VW had given in to modern "non-info" gauges: my car is from 1993.
http://i451.photobucket.com/albums/qq232/fasto_tt/th_Dsc00907.jpg (http://s451.photobucket.com/albums/qq232/fasto_tt/?action=view&current=Dsc00907.jpg)
http://i451.photobucket.com/albums/qq232/fasto_tt/th_Dsc00908.jpg (http://s451.photobucket.com/albums/qq232/fasto_tt/?action=view&current=Dsc00908.jpg)

Fasttrack
07-21-2009, 01:03 PM
Slightly OT, but have you guys seen some of the features on the new Chevy trucks? For instance, if the temperature rises above a threshold value, instead of just registering on the gauge, the computer enters a "overheat mode" where it alternates cylinder firings - i.e. it drops the V-8 to a V-4 and alternates which four cylinders fire.

There were some other pretty neat little tricks the pulled. The downside is that it has no less than 6 onboard computers each with a very hefty price tage :eek: Luckily they offer an extended warranty plan that only costs you 50 dollars should you bring your vehicle in for repair. (You pay nothing for the extended warranty, unless something goes wrong. Then you pay a flat 50 dollar fee for the dealership to fix the problem. If they fail to fix the documented problem on the first attempt, you don't have to pay the 50 again for subsequent visits - so not too bad)

fasto
07-21-2009, 01:06 PM
Slightly OT, but have you guys seen some of the features on the new Chevy trucks? For instance, if the temperature rises above a threshold value, instead of just registering on the gauge, the computer enters a "overheat mode" where it alternates cylinder firings - i.e. it drops the V-8 to a V-4 and alternates which four cylinders fire.


Chevy/GM uses this for fuel economy as well, at least the 2007 Suburban I rented had this feature along with a readout of how many cylinders were in action.

Ford has the anti-overheat mode in the "modular" engine series (ie, 4.6L V8), from the beginning, I believe.

Fasttrack
07-21-2009, 01:09 PM
Chevy/GM uses this for fuel economy as well, at least the 2007 Suburban I rented had this feature along with a readout of how many cylinders were in action.

Ford has the anti-overheat mode in the "modular" engine series (ie, 4.6L V8), from the beginning, I believe.

Yeah I guess I should point out that when I say new, that is from the perspective of someone who thinks my '89 Chevy with OBDI is sophisticated ... :D

saltmine
07-21-2009, 07:26 PM
Yep, fasto, Ford did design in an overheat protection.
Some overpaid engineer designed the engine(s) in such a way that at high speed or heavily loaded, the cooling system cannot carry away the excess heat the engine is generating, so it frys itself. We had patrol cars that literally destroyed their engines during a high speed chase. When I asked Ford about it, they told me that they've issued a directive to all police agencies stating that running at high speed (ie: pursuits), the engine has a life expectancy of about 8 minutes, so, to rectify the problem, they suggested we tell all of our officers not to chase anybody or run "code" any longer than 7 minutes.
Of course, the pickups have another mechanism, at 240degrees+ engine temperature, they start blowing out spark plugs. So if you're towing something with your F-150, and you see a dent or two appear in your hood, you've overtemped.

speedy
07-21-2009, 08:08 PM
I've got a 2000 Silverado with the 4.8L engine. The oil pressure has always read just under 60psi whenever the engine is running. It DOES move about a needle width up or down in response to changes in engine temperature and speed.

I but is it really an idiot light in disguise?Roger

Wire in a piezo alarm - you will likely hear it way before you notice any oil pressure drop on the gauge. If you are in the occasional habit of leaving the ignition on it will notify you of that as well..

Fasttrack
07-21-2009, 09:01 PM
Yep, fasto, Ford did design in an overheat protection.
Some overpaid engineer designed the engine(s) in such a way that at high speed or heavily loaded, the cooling system cannot carry away the excess heat the engine is generating, so it frys itself. We had patrol cars that literally destroyed their engines during a high speed chase. When I asked Ford about it, they told me that they've issued a directive to all police agencies stating that running at high speed (ie: pursuits), the engine has a life expectancy of about 8 minutes, so, to rectify the problem, they suggested we tell all of our officers not to chase anybody or run "code" any longer than 7 minutes.
Of course, the pickups have another mechanism, at 240degrees+ engine temperature, they start blowing out spark plugs. So if you're towing something with your F-150, and you see a dent or two appear in your hood, you've overtemped.

LMAO - Is that why the local police department axed their Ford fleet and switched to Chevy? :D <runs away laughing>

A.K. Boomer
07-22-2009, 05:06 AM
Of course, the pickups have another mechanism, at 240degrees+ engine temperature, they start blowing out spark plugs. So if you're towing something with your F-150, and you see a dent or two appear in your hood, you've overtemped.

This simply cannot be true, unless you can convince me that they are using the same kind of temperature lead that fire systems use when it melts and their using it for the threaded bores that hold the spark plugs:rolleyes:
Or is it plastic cylinder heads? or did they go with a new alloy that contains silly putty...

wierdscience
07-22-2009, 06:01 AM
No,it's what happens to alot of engines at higher altitude:rolleyes:

From having run a Crown Vic ex-cop car 140mph for 60 or so miles I can attest to the 4.8 durability.With three cooling fans and 5" of radiator and coolers it had no problem at or near sea level.

saltmine
07-22-2009, 10:00 AM
Actually, no lead was used. The dimbulb engineer that designed the cylinder heads thought three threads were sufficient to retain the sparkplugs against the engine's compression. Then, at the factory, the wrong torque was applied and the plugs would eventually loosen, threads fail and POW! out come the sparkplugs. This was common on all "Modulars" except the V-6, which had other problems to deal with.
Weirdscience, you couldn't have run an ex-cop Crown Victoria at 140mph, for any length of time unless the ECU had been reprogrammed. First of all, the US Brotherhood of Police Officers mutually agreed in 1998 to limit the top speed of ALL police vehicles to 122mph...including the Crown Victoria.
If you drove an earlier one, chances are it had been modified to deal with the excess heat problem. What happens is the ring lands on the pistons get so hot that they crumble, and pieces start flying around in the combustion chambers....eventually they damage the spark plugs, but by then a good portion of the piston has failed. 4.6L Ford police car engines didn't have the "blown out sparkplug" problem because replacement engines had steel inserts for the plugs to screw into...with more secure threads.
I've never seen a stock P-72 Ford Crown Victoria with more than one cooling fan, and one 2.5" thick radiator.
I have seen a Crown Victoria run well over 140mph, though. A guy out in California had one which he transplanted a Chevy LS-1 out of a Corvette into.
With the LS-1 engine and transmission, it would easily top 150mph. But, the chassis and suspension were not designed to handle the added stress of that much power. BTW, running at 140mph for 60 miles takes 2.5 minutes...

A.K. Boomer
07-22-2009, 10:54 AM
Saltmine what school of math did you go too? Or are you the product of being schooled at home? (in that case you better give your parents the "news")


"BTW running at 140mph for 60 miles takes 2.5 minutes..."








EDIT: I do have to add that if what you say is true about the plugs/threads and what I read about the gauges im so glad I made the choice to work on nothing but Japanese a couple decades ago -- very wise choice for all kinds of reasons.

A.K. Boomer
07-22-2009, 11:09 AM
No,it's what happens to alot of engines at higher altitude:rolleyes:

From having run a Crown Vic ex-cop car 140mph for 60 or so miles I can attest to the 4.8 durability.With three cooling fans and 5" of radiator and coolers it had no problem at or near sea level.


N.A. engines (normally aspirated) produce less heat the higher the altitude due to being automatically de-tuned the higher you go up -- the air is a little thinner for cooling but the effect is marginal as compared to the lower engine power output --- Now if your talking hard work and going nowhere hills are a tough act to follow but still engines are de-tuned and the electric cooling fans and heat activated fan/clutches are not, they may be slicing through thinner air but their RPM's go up in the process and they compensate some while engines take a drastic hit in perf. which equates directly to lowered heat energies.

saltmine
07-22-2009, 03:27 PM
MY bad. That's what happens when you try to do math with a hangover.
At 140mph, you're doing 2.3 miles a minute, so, to go 60 miles it would take 26.08 minutes. Most 4.6 Crown Victoria engines would have been toast right at the 10 minute mark, regardless of where you were running it.
These engines do have a problem throwing off excess heat under extreme situations. Not a fault of the cooling system, the heat can't be dissipated in the cylinder heads or block..Besides, police calibrated Crown Victorias would not shift into overdrive unless the driver released the throttle momentarily, at high speed.....GM had a similar problem with early Vega engines developing "hot spots" under the head gasket. This was solved when Ed Cole took a Vega block and cut slots between the block surface where the cylinders meet the gasket, allowing coolant to pass between the cylinders, eliminating these "hot spots". Vega engines machined this way never had the dreaded overheating problems early engines had.

saltmine
07-22-2009, 03:35 PM
In order to remove heat from an engine, the heat has to be capable of transferring to the coolant. On Ford "Modular" engines, the surface area for heat dissipation is smaller than the amount of heat that builds up. No amount of coolant passing through the head can carry away enough heat, to maintain a stable temperature. This problem is still there, today, and Ford continues to deny there is any problem with these engines. One has only to ask the owner of a Class A motorhome powered by a Ford 6.8L V-10, and they will tell you which engine they're on now...and it's never the original.

Willy
07-22-2009, 05:21 PM
The Ford spark plug repair is an infamous problem.
Not covered under new car warranty either.:eek:
Here's the Ford TSB in .pdf format.

https://www.fleet.ford.com/showroom/CVPI/pdfs/TSB072102SparkPlugThreads.pdf

A Crown Vic I wouldn't mind having.

http://www.gulfgt.com/forum/showpost.php?p=114311&postcount=1

Bob Bondurant, a former race car driver, has a world famous driving school. For several years he used a fleet of these highly modified Crown Vic police cars as instructor cars.
The cars started out as police interceptor cars from Ford and were then sent to Roush Industries were they received significant modifications to bring them up to Bondurant's specs.
These cars have been retired and now are highly prized collector cars.

.