56 F100 fuel gauge


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By wellcraft17 - 12 Years Ago
I've had an ongoing issue with my fuel gauge for years not reading correctly at speeds of 45 and up. It always acted up in the summer and not the winter leading me to believe it was a humidity issue with maybe an electrical problem as I live in FL and we do have corrision due to the salt environment. In the winter it would read correctly however in the summer it would read 3/4 when the tank was full and 1/2 when the tank was 3/4 full, at speed, and when slowing down and stopped it would read correctly. I replaced all the wiring to and from the sending unit and gauge and swapped out the gauge and sending unit with two others I had and still had the problem. Well, this morning it was cool and I was doing about 60-65 M.P.H. and the guage was reading correctly, this absolutely drove me nuts. As it was starting to warm up I opened the cowl vent and was amazed to see the fuel guage drop from full to 3/4 tank. I repeated this about 10 times and each time it would drop and then go back up when closed. That explains why it only happens in the summer and not the winter because I don't open the vent in the winter. I can only guess that the wind coming into the vent is somehow affecting the fuel guage. Has anyone ever encountered this or heard of it and what was done to fix the problem? I know I could drive around and never open the vent but thats not practical here in FL.
By bergmanj - 12 Years Ago
The gauge is a King-Seeley "hot-wire"-type (research [my] previous posts regarding how the whole system works); so, if there is air-flow right past it, it is conceivable it would cool-down the hot-wire and affect the reading.  I'd suggest to find some way of blocking air-flow near the gauge (behind the dash) & see whether that will help the situation.

Regards,   JLB

By wellcraft17 - 12 Years Ago
Thanks JLB that's exactly what I thought about and did. Problem solved, makes me wonder what the dealers did back in the day and if maybe there was some bulletin out on it. There is alot of air going through that vent it had to be a systemic problem but I've never seen anything written on it.
By bergmanj - 12 Years Ago
It probably wasn't a "problem" for most folks "back then": Most folks (especially those that needed to drive trucks - farmers come to mind) then knew that gauges like this were just "guides"; and, NOT precision!  THEY actually PAID ATTENTION to the "goings-on" with their individual vehicles (call it vehicle "personality", if you will); and, made their own personal "internal adjustments" to compensate.  Gee, what an idea!!!

Unfortunately, most vehicle gauges nowdays are also just "guides"; but, most folks (even my other half) now want to insist on taking those indicators (very foolishly) as "gospel": They are only guides, with maybe 20% "precision" at best!  Cheaply made to look impressive (to make sales); thats all.

Regards,   JLB