Gas gauge goes crazy on long road trip

Factual Questions
1

I drive a 1992 Nissan Maxima, and live in Alberta, Canada. A few months ago, I drove down to visit friends and vacation in Phoenix, Arizona. All the way south, everything was fine. But once I got to Phoenix, and on the return trip north, the gas gauge on my car went berserk. Without warning it would go from 3/4 full to indicating completely empty. Five minutes later it would be back at approximately the right level. Sometimes it would visibly rise and fall like a wave on the ocean. There was no apparent correlation between this behaviour and when I filled up, or what grade of gas I used - I was alternating between premium and mid-grade to save money.

Once I got home and resumed using my usual brand of gas, everything returned to normal. When I asked my retired petroleum executive father he mumbled something about specific gravity, different gasoline formulations, and waved his hands a lot.

So what’s the straight dope on why my Nissan went loco in Phoenix?

2

If it didn’t happen except on the return trip, I’d say there’s a short in the system somewhere.

3

" I’d say there’s a short in the system "

Yep. Most likely in the guage or the sender.

4

Anecdotal, but my gas gauge does this and it’s definitely an electrical short.

Oddly, it only does this when the gas tank is more than half full. Once the tank has reached half full, the gauge goes to maximum, then comes down slowly, always reading about twice as much gas as is really in the tank. So it’s still useful, I just divide by two.

mischievous (who has a car with many quirks)

5

But why would this fault only manifest itself when moving south -> north, and when crossing borders? When I move in any direction north of the Canada-US border, everything seems to work normally. Is there a Star-Trekkian gasoline flow force that only takes effect south of the border, down Mexico way?

6

Clearly filling your car with US gallons of gas confused it as it wsa expecting liters. So next time you take a trip here bring some liter bottles and first dispense the gas into the bottles then poutr it into your gas tank.

7

I’ll hazard a guess that the dashboard gauges are managed by an electronic voltage regulator, separate from the VR in your charging system.

My truck will occasionally tell me the temperature is off scale, I have a tank and a half of fuel, and the oil pressure is ready to blow the head gaskets. Toggling the front/rear tank switch returns the gauges to the land of sanity. The Ford manual indicates dashboard VR at fault, but pulling the dashboard is a PITA, so I live with the workaround. :wink:

8

But is that an Imperial gallon, a U.S. gallon, or a metric gallon … computing …
ERROR … DOES NOT COMPUTE … SUBMITTING TO YOUR WILL James T. Kirk … DOES NOT COMPUTE … My God, It’s Full of Stars … EXTERMINATE, EXTERMINATE … <shower of sparks> … Daisy, daisy, giivvve meeee your annnssssswwwweeeeeerrrrrr dooooooooooo …