Why our Oil Pressure Gauge is worthless...

[Ron]

<FONT face="Comic Sans MS">As many of you have no doubt observed, the stock oil pressure gauge virtually worthless. It is inaccurate, extremely slow to respond and really just nice decoration.

I my quest to keep the stock look, but make it truly functional, (while keeping it electrical rather than mechanical) I have tested the sender and gauge to identify the culprit.

Unfortunately, it's both.

The stock sender increases resistance as oil pressure increases, from about .4 ohms @ zero to 60 ohms @ 60 PSI. The issue with the sender is twofold. First, you'll get a 12% average variance as you move up and down in pressure. For example, at 25 psi, you'll get a reading of 32.2 ohms on the way up, and 36.4 on the way down. You'll freeze at 50 PSI, but the sender with drift up and down 4 ~ 5 ohms. Worse, if you pressurize the system to say 65 psi, then rapidly dump the pressure to zero, the sender with take almost 6 seconds to read .4 ohms.

For comparison, I took a 32 year old oil pressure sender out of my 1970 Trans Am and mounted it in my test rig. While it wasn't perfect either, it was rock steady when the pressure froze and dropped to zero immediately on a pressure dump.

The gauge itself, shown enough resistance to read 70 psi then immediately shown zero ohms, took 3 ~ 4 seconds to register zero.

The gauge problem is silicone grease. It's a sticky thick fluid that is only removable by destroying the gauge.
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The only solution I see is swapping out the gauge guts with a better design and replacing the sender (1/8 NPT 27 thread) with a higher quality unit. This should enable a stock look with the responsiveness needed to provide functionality.

Has anyone already accomplished this or able to give additional insight?


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[Mike L]

Ron, I have a couple of comments:
I don't always watch the guages every second I am driving. I make it a point to look at them regularly but most likely several mins pass between each glance. I would really like to have a audible buzzer go off if I were to lose oil pressure suddenly. I have this feature in all of my company's trucks. I think this would allow you to take notice and shut down before any engine damage would occur. As for the slow response of the factory guage, I doubt a six second improvement in response time would help me out. Shouldn't the synthetic oil keep things together for a short period of time anyway? What do you think of creating an audible signal for low or lack of oil pressure?

Mike

 

[Ron]

<FONT face="Comic Sans MS">Excellent idea Mike, though given the potential loudness of the exhaust and stereo, plus the fact that the buzzer would go off every time you start the car, (before the oil pressure passes 8 psi) I prefer my "Blue Light Special":
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I wired in this extra bright LED into the idiot light circuit so whenever the engine has less than 8 psi, the light is on. It is more than bright enough to see in daylight and catches your peripheral vision easily, even if it just blips.

While I agree that the light / buzzer is all you really need, I find a responsive gauge useful as it can show:
<UL TYPE=SQUARE>
<LI>When your oil is warmed up
<LI>When the viscosity is too high for the temperature conditions
<LI>When the viscosity is too low for the temperature conditions
<LI>Brief blips in pressure do to pickup stavation
<LI>Weak oil pressure relief valve
<LI>Stuck oil pressure relief valve
<LI>Etc.
[/list]
6 seconds of zero pressure at redline I believe would be catastrophic and while I don't stare at the gauges either, I do have a habit of glancing at them under heavy braking, hard cornering and rapid acceleration looking for anomalies. Unfortunately, in the case of the Viper, there is no need.
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[Joe Dozzo]

Have you looked at Autometer's Phantom series gauges?

I've replaced my 98 GTS gauges with them and they look very nearly stock. While I enjoy having generally much better / accurate gauges, I do have two little complaints:

1. The lights at night are a bit more reddish that the factory lights (and getting the right color has not been worth the bother yet)

2. The gas gauge and Viper sending unit are close (the gauge does read full when it is full!), but it falls off like a rock. As a result, I use miles to decide when to get gas.

Installation took the best part of a day.

 

[Ron]

<FONT face="Comic Sans MS">Joe,

I have an obsession with keeping the car "stock" looking and prefer to gut the factory gauge (especially since I now have an unintended donor) and replace the mechanism with the guts of an Autometer for example. Plus, I do like the OEM lighting as you mentioned.

If I find it more trouble than it's worth, I might go your route, but I'm pretty stubborn.....</FONT f>

 

[Robert Dyck]

Ron.....I would expect a delay or lag in oil pressure within the engine. Why do you think that oil pressure should react faster, according to the other gauge?

 

[Ron]

<FONT face="Comic Sans MS">Two reasons, both unscientific.

One, experience. My 1970 Trans Am has an electric OP gauge that response instantly to oil pressure changes. If I'm a quart low and slam on the brakes, the gauge flutters low. If I'm at idle the gauge reads 30psi, at 3,500 rpm the gauge reads 60psi. It's almost mirrors the tach itself at the lower rpms (until the relief spring begins regulating the OP). If the oil is cold, the gauge is pegged at 80 psi until it warms up.

My Viper gauge is at 50 psi hot / cold / idle / 6,000 rpm. The only time is moves is when it's over 90 degrees at idle and then it reads 48 psi. Oh, and when the engine is off it reads zero.

Second, the oil pressure sender is in a position to measure the pressure very close to the relief valve. Given that, it should respond to system pressure changes almost instantly.

Again, not scientific (I'm a marketing guy, not an engineer) but logical to me at least.</FONT f>

 

[Robert Dyck]

Well, it could be that the old 70' gauge is reacting too quickly, whereas the modern gauge has a more controlled and accurate indication.......??

Since oil is, for the most part incompressible, I would expect to measure immediate change in oil pressure within a simple vessel. But I'm not sure how it would react in an engine, and how it may vary depending on where the reading is taken.

Why is it important to see such immediate changes?

 

[Ron]

<FONT face="Comic Sans MS">From my observations, there is nothing accurate about our gauge.

If a gauge is to be useful it needs to accurately and immediately reflect reality. Ours does not. I don't see any advantage to damping the pressure reading so much that the gauge basically has two positions, 50psi or 0.

While there may be a latency in the entire engine oiling system, that doesn't change the fact that the sender, stand alone, has a 6 second delay and the gauge, stand alone, has a 3 ~ 4 second delay. They both should have no delay, thereby reflecting the true engine system pressure at any given point in time.

Perhaps it's just my car, though from conversations and observations of other Vipers, I doubt it.</FONT f>

 

[GTS Dean]

Ron,

The silicone is in there to cushion the pressure spikes because internals don't last long if they're too sensitive. Apparently, there's a hysteresis in the silicone that isn't linear. Lots of the sending units have a very small orifice for the oil to push through. Since you've had a Viper sending unit apart, is it possible to use a pin vise and open the orifice up some? As for the slow gauge "return to zero" - electrics ain't my game.

 

[Paul Fischer]

What Joe said.

I used the same setup in my GTS that he has. The first day at the track after the swap I did a comparo betwen Mobil One and Royal Purple. The Autometer's were able to give much better reference points with their better gradation on the face and responded much more quickly. The fuel level send unit has to be replaced for the gauge to report accurately which is a pain (Sean Roe has posted on this installation) but the gauges are worth it IMHO. I also think that they look much better than the stock units which have no place in a $70k car.

The only appointment in the cabin of a Viper that is truely worthless is the rearview mirror.

 

[Ron]

<FONT face="Comic Sans MS">Dean;

I did not take the sender apart as there is no way to do it without destroying it. The picture about is the spindle of the gauge itself.

Looking at the Viper orifice though, it's quite large, especially in comparison to the old Pontiac one, which is barely more than a pinhole. Surprising, the pinhole works better, so the slow leakdown must be something internal in the Viper sensor or a very small, not externally visible internal orifice.

While I agree that you would not want an undamped gauge, the selection of heavy viscosity grease seems a bit excessive.

Paul;

Ultimately, I might follow the path of Joe and yourself, but I don't have a problem with the look or functionality of any other gauge, so for now I determined to find a fix for it only.

Thanks guys....
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[shifter]

The modern gages are a result of giving the driver enough information to see all is well, but not too much info to rack up unnecessary trips to the dealer and warranty costs. The industry tried reverting to more "idiot lights", but the general public felt uniformed about what was going on with the car, especially as cars got quieter and more sophisticated.

The more accurate the gage, the more erratic it's behaivor, and thus the higher the warranty costs are due to a lack of mechanical understanding in most automobile consumers. If it weren't for the auto mags conceptualization of the ultimate vehicle, the automakers would prefer 1 single light "O.K." or "not O.K. go to dealer". Takes the error out of the consumer group.

 

[GTS Dean]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Ron:
[BThe picture about is the spindle of the gauge itself.

While I agree that you would not want an undamped gauge, the selection of heavy viscosity grease seems a bit excessive.

[/FONT][/B]<HR></BLOCKQUOTE>

OK, I understand the situation now. Perhaps you could use a hypodermic syringe to ********* the membrane and extract and replace the silicone with something that has lower viscosity. Then, you can Super Glue it shut.

Or, you can trace down the supplier for the gauges and see if they have a lighter, more responsive unit.

 

[Viper Specialty]

well, at least on my car, and my views, I can add a little. first, my gauge is 100% dead on. I have an accusump with a mechanical, liquid filled gauge, 60=60, and so on. also, one reason that the Viper gauge may never move very much with RPM is that the oil pump we have is OVERKILL, meaning it is using the bypass valve, even at idle. our problems are not with oil pressure due to the pump, the vipers problems are due to oil pickup starvation, which is the result of us racing our cars at high G's and sucking up air. just get yourself some baffles, an accusump, and keep an eye on your gauge and idiot light, and dont worry about it. Accusump will give you 45 seconds of oil if you make the 3Qt. fit like I did! more than noticeable on the gauge, and still gives time for safe shutdown if there is a real failure.

 

[FRANK]

Man,

I never knew an oil pressure gauge could cause so much controversy...ohms, variances...if people are so concerned about losing oil pressure just buy an Autometer Pro-Lite for oil pressure and when it goes below like 10 psi it shines red. Under $30...plus the general rule of thumb is 10 psi for every 1,000 rpms...

 

[Ron]

Surprised to see this thread resurrected after a year.

Daniel, Regarding overkill, you could be right however that still doesn't excuse the gauge's inability to rapidly report pressure changes. The needle is way too unresponsive to provide meaningful data. Just observe the delay on startup and shutdown.

Sure an accusump would work fine, but adding more plumbing to the oiling system also increases risk. I've seen more than one system blow under pressure. Add to that the cost and placement issues, though if racing I'd agree probably worth the risk.

Frank, Always happy to provide some entertainment. My homemade blue light special above is exactly what you describe and it provided me an hour of enjoyment rigging it up.

For me the bottom line is this. I enjoy toying with these kind of things. I find it stress relieving and gives me something to do when it's cold outside, though I admit, it doesn't solve the world's hunger crisis. In addition, I feel that if a car has gauges, they should work and in my opinion the stock oil pressure gauge doesn't work. It's really just an ornament. Understanding why it was designed that way (unneeded service visits and warranty issues) is great and even acceptable on a Neon, but not on a Viper.

 

[Viper Specialty]

RON- the BIG reason to get an accusump is not only its accumlatory function, but also its Pre-Oiling ability...that in itself makes it all worth it. Nothing like NEVER having to start your engine dry again. Also, seeing the true Accusump system up close and toying with it quite frequently, you will easily see it is a definate, trustable system. This thing is built to take a round from a M1-A1!

Also, the idiot light responds qickly if there is a true problem, and I would venture to say that light, or a setup like yours, it easier to see than gauge would be.

 

[Ron]

Daniel;

Agree 100% on the idiot light as the best indicator of pressure loss. In prior cars though with more responsive gauges I found it informative to see when the oil warmed up, the pressure variances with different weight oils, even relief spring issues. But you are right, the light is most important. It just needs to be in a spot where you'd notice a blip.

On the startup issue, I again agree and was going that route myself when I spoke with a few experts (oil industry and PVO) that felt the anti-wear additives in modern engine oils made the pre-oiler unnecessary. Even when the oil drains back into the pan, I'm told that the AW additives stay behind and more than cover the start-up. So rather than add the complexity of a pre-oiler, I changed to Mobil's synthetic diesel oil Delvac 1, which has a higher AW additive package the Mobil 1.

Better than a pre-oiler, probably not, just the route I chose to go.

Let get together at 100,000 miles and compare!

Even better, on your next oil change, why don't you send a sample to Blackstone labs for an analysis and I'll send mine. We will be able to see from the wear numbers if the pre-oiler is superior to Delvac 1. I'll even pay for the analysis because if it is better, I'll go the pre-oiler route too!

Free Sample Kit Here

 

[Viper Specialty]

RON- just may do that! however, we may not be the best specimens, as I doubt our mileages and engine histories are anywhere near the same. I change every 1500 miles as I get oil changes for free, and I only have 6K miles, not broken in completely yet.

 

[Ron]

Another valid point, but what the heck we should try anyway.

I have 12,000 miles on the car, engine stock with only smooth tubes on it right now. Had K&amp;N's for a while and rear muffler delete but OEM back on for now. Also change oil too often, about every 2k miles. M1 10w-30 all the time except for last summer with 15w-50 M1 and now 5w-40 Delvac 1. Change oil typically every fall before storage. Use M1 oil filters. Did upgrade the oil pan / windage tray to 2000+ so we both have the 10qt capacity, but kept the OEM oil filter adaptor as I do drive in winter temps on occasion.

With the exception of year, we're not too different.

 

[Viper Specialty]

6K miles here, S&amp;B Filters, M1 and M1 Filters. (just switched from Napa Gold). Also have baffle kit in oil pan, and just installed the Accusump system. I use an ACR filter adaptor as it is neccisary with the Accusump. I intend on going with the Archer radiator with an internal oil heat exchanger VERY soon however, so I am good for winter runs with the ACR adaptor. I have only driven car once since adaptor, accusump, and baffle install. was 35-40 degrees outside. One thing I just thought about though, may not be a good idea for me to test until after one more oil change, as all of my latest mods included LOTS of application of Loctite, and I would be willing to bet the chemicals in loctite will throw the tests off until it finishes dissolving into the oil from the thread ends. I figure next oil change will be May-June. (BTW, I did order the oil kit)

 

[Viper Specialty]

PS- I gained 6 PSI at IDLE with filter adaptor! I now sit at about 57-60 for HOT idle. (according to my mechanical gauge, this is DEAD on.

 

[Ron]

Sure, the loctite could throw silicon values up.

Sounds like you have a good plan going, but much more extensive then I plan.

My pressure reads on the OEM gauge 50lbs hot, cold, idle or 6k rpm. It's 0 when the engine is off and on really cold days it take 5 minutes or so for the gauge to move the final 10 psi to 50 as the oil in the gauge itself needs to warm so the needle can full reach it's target.

Maybe it's just that the 1996 OP gauges are crap and the 2002's are better?
<font color="blue">
Anyone else have a Accusump or Sean Roe's oil accumulator that wants to share oil analysis result? I would be the first to buy one if the results showed significant wear reduction.......

</font>

Thanks

 

[Edward 96GTS]

For a 96 GTS what should the stock gauge read at:
1-start up?
2-idle when hot?
3-normal driving?
Thanks

 

[GR8_ASP]

My oil pressure on the '95 is about 40 psi hot idle and goes up with engine speed to around 60-65 psi. It reaches 60-65 psi at around 2000-3000 rpm. With the oil cold the oil pressure is around 70 psi. Based on the responsiveness in the reading when blipping the throttle at idle I would say mine definitely does not have a 10 second delay.

Not enough time in the SRT yet to understand the pattern but it is not significantly different. But I do like the addition of the oil temperature gauge.

 

[Edward 96GTS]

bump-Any more responses re stock gauge readings?
Thanks

 

[Viper Specialty]

mine sits at 50 Hot idle, Same pressure for cold idle. May jump to 55-60 or so with higher RPM. However, I have a true mechanical gauge on my Accusump, and it shows I am ACTUALLY making 65 on hot Idle, 65 on cold idle, and 70-75 at 3K RPM.

 

[Ron]

Then the mechanical reads at a 30% variance to stock. Nice OEM gauge. I'm sure the mechanical responds to pressure changes a bit faster, i.e. instantly. Too bad you can't see it while your driving!

One of these days I'll figure out a way to get a stock appearing gauge to be useful without going the full mechanical route, (which would mean bringing an oil line up behind the dash, not something I want to do).

 

[Edward 96GTS]

Ron,
What should the stock(96 gts) guage read at:
1-start-up idle
2-hot idle
3-cruising rpm
Thanks