Like it’s really that hot

Not that you were going to or anything, but if you pointed at my car’s dashboard and asked me “What’s the least-accurate display here?” I’d tell you, without hesitation, that it’s the gas gauge: the last time it bottomed out, the subsequent refill took just under 15 gallons — for a 70-liter (18.5-gallon) tank.

But people don’t post pictures of their gas gauges on Facebook, so this is the complaint:

When the mercury hits the levels we’ve seen in recent days it’s inevitable — someone will post a photo of their car thermometer on Facebook, Twitter, or Instagram. But how accurate are they?

“They’re parked on hot blacktop; there’s going to be residual heat from just the engine itself, the car may not be moving,” said Bill Linsenmayer with AAA Ohio.

He estimates they’re about 5-10 degrees off from the official temperature measured by the National Weather Service.

Which is specious, unless you happen to be driving past the official National Weather Service weather station. In Oklahoma City, you’re not; it’s tucked away into a corner of Will Rogers World Airport. Out where I live, just off the heat island that is Penn Square Mall, being five to ten degrees off is routine.

Besides, Nissan thought of these objections years ago, and set a delay circuit into the HVAC system I have. This time of year, it’s typically in the middle 80s in my garage at sunrise, and the car’s thermometer will so indicate; if it’s, say, 75 outside, the reading will slowly drop, a degree at a time, until it’s reached 75, somewhere near the mall. (At which time, it’s probably 70 at the airport.) In general, the little display is more accurate than the few remaining time/temperature signs around town: it was 96 degrees yesterday when I passed by a local church that claimed it was 105. (Hellfire and damnation, indeed.) And the only time I’ve ever seen it have problems was when the temperature was about -5, and it kept bouncing between -3 and -4.

Now how Nissan can get climate-control gizmos to do this and yet can’t build an accurate gas gauge to save its Qashqai is beyond me.





6 comments

  1. Francis W. Porretto »

    8 July 2012 · 8:35 am

    Gas gauges can be built to the most meticulous imaginable standards and still prove inaccurate in practice. There are all manner of post-design, post-fabrication effects that can and will distort them. Most common on passenger cars is blocked venting; the build-up of air pressure as the tank fills eventually becomes strong enough to trigger the backpressure cut-off on the pump, even with substantial room left in the tank.

    When I was pursuing my pilot’s license, I was told in the strongest possible terms never to trust the gas gauge. Judging from the number of private pilots each year who have to make emergency landings because of fuel exhaustion, I’d say it’s good advice.

  2. McGehee »

    8 July 2012 · 9:12 am

    Since my gas gauge’s inaccuracy reached 1.00 mere months after I got it, as a result of a fuel pump replacement, I’ve been using my tripometer to determine when to fill up.

    In general the fuel amounts I put in at the gas station relate to the tripometer reading on the order of 13-point-[mumble] mpg, which on a 25-gallon tank, if I leave out the [mumble], works out to a 325 mile range. And since I usually get antsy to refuel by the 300-mile mark, I’ve never run out.

    Which may explain to some extent why a gauge on an 18.5-gallon tank bottoms out at 15 gallons.

    And I’ll bet anybody who compares their speedometer to the speed reading on their GPS that they’re actually going noticeably slower than the dashboard needle says. Same reason. So if you routinely put the needle five over the limit and never get a ticket, the joke may be on you.

    Someday a carmaker will use GPS to inform the dashboard speedometer though, and we’ll all be in trouble.

  3. CGHill »

    8 July 2012 · 9:52 am

    And if you run out of gas with one of those submersible fuel pumps that rely on the liquid flow for cooling, the results are decidedly suboptimal.

    I have attempted on occasion to use the handy mile markers on the freeway to determine the accuracy of the speedo/odo combination. It is close, but not quite spot-on.

  4. fillyjonk »

    8 July 2012 · 1:32 pm

    I still say that we just label everything over 85 or so “too damn hot” and stop counting degrees. (The three banks I drive by on a typical trip to the grocery all always have different readings. Then again, their clock functions do not agree; at least two differ by five minutes).

  5. Daily Pundit »

    8 July 2012 · 9:02 pm

    Tanking It…

    On my Rav4, that irritating gas warning light will come flashing on with anything from three to four gallons left in a sixteen gallon tank. So … a 25% error factor is acceptable to auto makers when it comes to your gas gauge?…

  6. Jeffro »

    8 July 2012 · 9:54 pm

    The temperature monitor on the 9900i is somewhere under the hood – it’s always at least three to five degrees higher than anyone else’s reading, plus when the fan kicks in and starts blowing hot radiator heat back to the firewall, it can get ridiculous. I’ve had it read 130 degrees when it’s just 95.

    If I or anyone I know ever found the thing, I’d move it. So far, no.

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