I drove a VW Tuareg today. I noticed that there was a Voltage gauge and an oil temperature gauge. I thought that’s cool, you don’t see these in many cars today.
I noticed that while idling the needle was at exactly 14 volts. I thought that was a bit high for idling. I revved the engine a little and the needle didn’t move at all. I turned the rear defroster on and the needle still stuck at exactly 14 volts. I could hear the engine sound change and the revs drop slightly as the load on the alternator increased but the fucking stupid needle was not moving at all! :smack:
So, the gauge was so heavily damped to be practically useless. I didn’t drive the car long enough to warm the oil, but I guess the oil temp gauge would be equally useless.
Same goes for water temp gauges. Nowadays they practically have only three positions: Cold, Normal, Replace gasket. I drive a 1970s car and I can see the temp gauge rise slightly when waiting at the traffic light and then drop again when the car moves.
Why do car makers do that? Do they think that Susie soccer mom’s head will overload and assplode if there’s a fucking gauge that actually works on that instrument panel? Oh noes, the needle moved, there must be something defective with the car lol, lol !!!111!!one
Yes, and they’ve learned this through experience. Having to eat the costs of a warranty service call when there was nothing wrong is a very effective deterrent.
If the engine is running, isn’t the voltage set by the voltage regulator on the alternator? I don’t see why it would change depending on engine speed or the number of accessories you have turned on.
Why do you say it’s useless? The purpose of the gauge isn’t to give you jollies while you watch it bounce up and down as you rev the engine and turn crap on and off. The purpose of the gauge is to let the driver know when something is broken. Having a highly sensitive gauge with a needle that regularly goes up and down when nothing is broken is potentially a poor indicator of when something is broken.
You’re not flying the space shuttle here, you only need to know if the battery is worn out, the alternator is broken, or if the wiring isn’t connected tightly. You don’t really need to know that the voltage had a 1 second spike to 15 volts and a 1 second dip to 12.
Exactly. Even if the gauge is heavily dampened so as not to disturb people seeing constant minute variations in the voltage measured at the battery terminals, how do you know that it wouldn’t work to indicate to your that your battery or alternator really was dying over, let’s say, a 10 minute time-frame?
I had an alternator fail in my Honda Accord at the start of an hour long trip. I didn’t know this while I was driving until everything gradually dimmed and stopped working. If I had realized this sooner, I might have been able to avoid nearly stalling on the interstate and needing help from the police with a portable battery-pack to get home. At the very least maybe wouldn’t have felt as idiotic as I had for making half the drive with the radio turned on. So there would have been a hypothetically useful purpose for such a gauge, even if it’s heavily dampened.
At idle the alternator is not moving fast enough to generate enough current and the voltage is slightly lower. The service manual procedure for testing the alternator usually requires the revs to be at 2000.
Also I’ve seen many cars with too small alternators, eg having the high beam on and the alternator is barely giving out 13volts, even at high rpms.
On the dampening issue: The difference in the output of a good alternator and one that is about to fail can be as small as 0.5 Volts. If the needle is permanently stuck at 14 then the gauge isn’t telling you anything useful.
Ford has been doing this for years. My 1999 Explorer has an oil “gauge” that always reads the exact same pressure. When my sensor went out, I learned that it was nothing more than a glorified and pretty idiot light.
And when the alternator does fail, the voltage goes down to, what, 12 volts or so? And start to go down as the battery drains, but the car would still run on battery power for a while, wouldn’t it?
Anyway I think the point made by others is valid, that a too-sensitive gauge would only be a distraction and cause of unnecessary nervousness. The oil pressure gauge on my car is like that, it pegs at high RPM but goes down to maybe 2/3 of full scale when idle after the engine has warmed up. The first time I noticed it I got worried and called a mechanic, who told me it’s normal. I still don’t see why I need to know the exact pressure - I’d think it’s enough to just warn me when it’s low enough to require attention.
Battery has very little to do with it. When the engine is running you are reading alternator voltage.
Yup.
Again yup.
You can’t make a blanket statement like At idle the alternator is not moving fast enough to generate enough current and the voltage is slightly lower.
How much voltage is being generated is strictly a function of battery condition, alternator size, and load on the alternator. I know of plenty of cars that produce 13.9V + at idle.
Excellent point. One time, my alternator gauge read 13.5V instead of 13.9V and I crashed into a tree. Of course, that was better than the time my oil gauge was reading too high, and I drove straight off a cliff, boy did I have egg on my face that day!
So does my 2008 Mazda RX-8, and the consensus on RX8Club.com is that it (the gauge, not the car) is quite useless. It would be wonderful if it told me when I need to add oil, instead of leaving me to grapple with the dipstick every other fill-up (which has lazily morphed into once every month or two). With the way RX-8s tend to use oil, an oil pressure gauge that indicated something other than “your engine has at least one drop of oil in it” would be immensely useful.
I had a 1991 Pontiac Sunbird with a full instrument cluster on the dash. I used to get a kick watching the Voltage gauge beat in time to the pulsing of the turn signal. I guess that meant it worked OK.