Gauges....Which ones do we really need?

[madizell]

All of the gauges I have used in the past ten years have been consistent (reasonable precision) as well as reasonably accurate, with the exception of the problems I have had with the digital gauges, mentioned earlier or elsewhere. Auto Meter gauges have proved to be both consistent in terms of repeatability (precision) and show values that comport well with reality (accuracy). Don't know why you have had problems with gauges.

Warning lights are for drawing attention to problems, not for relaying usable information. Example, you have pre-set your warning light to come on for whatever it is you are tracking, and the light is NOT on. Is there a problem?

You don't know, because the light is not on. Perhaps the light is working, perhaps not. The sender could be dead. The wires could be broken or disconnected. The light could be burned out. How are you going to know?

If you feel you must have warning lights because you don't trust your gauge scanning, buy gauges with warning lights built in and set them where you want them, so you have both a constant read out of value and a warning light in case you forget to look at your gauges.

 

[ntsqd]

I did not see it as a hijack. You asked which ones do we really need.
For a gauge pod like what you're looking for try looking up sheet metal shops. Specifically look for those that do work beyond HVAC stuff. Were you more local I could recommend one in Oxnard and another in Carpenteria.

I never said that gauges don't have some value.

I don't really think gauges are all that great of an idea.

EXACTLY. I do not think they are all that great of an idea, but that does not mean that I think they have no value. I've pretty much said and re-said my reasons why. I'll leave it at that.

As to whether the light works or not, there are ways to simply test that, but ignoring that, how do you know that the guage isn't lying to you too? Simple truth is that a reading on the guage only means that the gauge system is functioning, not that it is indicating correctly. Having seen needle on the oil pressure gauge that the PO installed in my new to me VW diesel clear back around to zero means that it is indicatiing, but I've no faith that it is indicating correctly.

At the aircraft level of quality (& cost) I would trust them to be accurate. They very likely have spec sheets that tell what their midspan and full range error percentages are, or that info is available from the mfg. Unless educated on the topic the gauge(s) that most people are likely to buy have no such sheet and therefore have no guarantee of accuracy. Good or bad, what you get is what you get. And how would you know?

 

[IllianaXJ]

My XJ has most of the gauges I need stock; Tach, Volts, Fuel Level, Oil Press. and Coolant Temp. I plan to add a Trans. temp gauge eventually. Chrysler was nice enough to make the gauges actually have numbers on them, opposed to H or L.

In my old XJ, I mounted a trans. temp gauge and an air pressure gauge to monitor my OBA tank pressure. I run a CO2 cyl. in the new XJ, so no air pressure gauge is needed.

I installed a cheap mechanical trans. temp gauge in my Expedition as well to monitor temps while towing. It may not be 100% accurate 100% of the time, but the Expy doesn't have an idiot light for trans temp, so it's better than nothing.

 

[madizell]

I have never seen anything to document that aircraft (at least GA) systems and equipment are more reliable than similar systems and equipment available for automotive applications. There is a difference in cost, to be sure, but the additional costs attendant to aircraft systems arises from FAA certification, not from costs of construction or levels of engineering. Indeed, many of the components on GA aircraft can easily be replaced at NAPA -- except they won't pass FAA inspection because they lack a certificate. There are numberless examples of exactly identical components made by exactly the same people with exactly the same parts selling both as aircraft parts and as automotive parts. One part will have a certificate and cost 5 times as much as the other, but there will be no other difference.

Arguing that gauges lie about details is pointless, in my opinion. Lights, gauges, all rely on senders and wiring similarly subject to error. It is like arguing the difference between a gauge and a meter. The technical parameters for determining the usefulness of a readout are accuracy and precision, which are not the same thing. None of the gauge, idiot light, sender, or sensor folks offer information on accuracy or precision. My guess is that it is not important within the market, and would be dependent in any event on details largely outside anyone's control outside of the experiment on which the accuracy or precision are predicated.

For example, you may have a gauge which gives you a high degree of repeatability (precision) so long as the input signal is within a related range. That is, X volts yields Y reading time after time. Fine, but how does the gauge manufacturer control the sender signal in your vehicle? Even if you use one of their own senders, manufacturing tolerance allows for small differences. Are these small differences important? Generally not. Does an erroneous reading on a gauge mean that the gauge is defective or imprecise? Not necessarily. But without data to go on and the ability to measure sender data, who can calibrate a gauge made by anyone?

I have flown a lot of aircraft over the past 37 years, and I had no more idea of the accuracy or precision of the gauges on those aircraft than on any car I have driven. For the most part whether the read out is accurate or not is less important than if the read out is within an acceptable range, and will reflect significant, important, or dangerous changes reliably. If a reading of 10 is good to go and a reading of 5 or less is not, whether the readout is 5 or 4 is moot -- both are unacceptable. You can quibble over the difference between 6 and 5 in that scenario, but the point is meaningless if you have been operating consistently at 10 for years and suddenly you see a 6. it is the 4 point drop that has meaning, not the exact value of the readout. If the difference between a 6 and a 5 is critical to you, stop and verify.

Our vehicles are so forgiving for the most part that we can safely drive them and ignore the dials and lights. That we don't scan gauges while driving cars the same way we would while flying a plane is an apples/oranges comparison. If the engine quits on the car, we get out and see what's up. If the engine quits on a plane, we usually have only a few minutes left to contemplate our sins. Still, it is not the scanning of gauges that keeps either motor running, so I tend to think the argument about lights and gauges is not technically based, but rather based in personal choice and a lack of understanding of what each can do.

 

[Grim Reaper]

Actually I side to some extent with ntsqd. I think a gage is great but after loosing oil pressure in my old Pontiac I think a combo of gage and a light might be a better solution.

When my Pontiac laid down the still enabled idiot light is what caught my eye, Then I confirmed a problem with the gage.

I watched a buddy idle in a very twisted up position for a while and asked him what his oil pressure gage said. Zero!

One friend has his idiot light tied into a piezo buzzer after similar experience.

I have been planning on adding a idiot light to my oil pressure circuit on the 4Runner. I have the switch but neglected to install it when I installed the motor. I have to lift the engine up and remove a motor mount to get it installed into a existing port.

 

[Gurkha]

I have oil pressure, turbo boost, EGT, tach, rpm and amp, apart from that I fully concur with madizell's point that gauges lie and can't be trusted as the final word. VDO senders for temp in MBs are notorious for going off whack as they age and sending wrong temp signals which mostly result in high temp readings of a perfectly normal engine. This would create un-necessary panic in their owners and this vagary is also documented in the MB forums. So its better to use common sense plus gauges. Fuel senders in diesels are another issue, till today, MB or Toyota engines can't design a properly working one. Due to the nature of diesels these expensive float cum senders in the tank would invariably start giving wrong readings about the fuel level leaving many stranded in the wrong place at the wrong time. Usually they would go bad and show the tank as half full when in reality you only got a few liters left.