Bought this Jaguar xk8 2001 and it happened to have a bad alternator which caused the dash to light like a Christmas tree. While I found most lights to be an actual problems other by improper power.

I have the alt on order but I noticed I filled the tank up and it wouldn't go up but the tank was full. Then it jumped to full another day and I drove to test the car for 5 mins and the gauge went down like it consumed 4mpg a gallon, mind you the fine is in pristine condition and doesn't leak any fluids, had a lot of work done to it including chains.

I'm just looking to confirm before replacement of the alternator whether it could be causing this. Thanks!

 

The dash has level gauge will not show the proper actual level in the tank if the sending unit in the tank is faulty, and many are. Mine only reads correctly when I’m on a cross country trip and using gas one tank after another in rapid fashion. I think the constant movement helps the sending unit read correctly.

Otherwise my dash gauge always reads lower than reality.

I use the “gallons used” info that is activated by the left steering column stalk to give me an accurate indication of the amount of gas remaining. I zero it out every time I fill up so I know precisely how much gas is remaining in the 20 gallon tank. It’s always been very accurate.

Hope this helps .

Z

PS: note, I have a lead foot, so my mpg is abysmal as expected. In town I get in the low teens and on the highway about 20-24 mpg.

 

NO......But you should fully charge the battery so that its 12.6v ish then do a reset and see what you have. All alternator faults other than a low voltage regulator show as glowing warning light.. You also need a good OBD scanner
Faulty tank unit is your problem. Dont even think about taking the tank out for access. Run the fuel right down or drain the tank at the fuel filter.

 

I've changed the battery with a new AGM one, the previous one in there was a small battery obviously not for the car. Fixed some issues but the gauge is bipolar. It works intermittently. Sometimes it will the fuel is empty, but I'd fill the tank and only be able to fill 14gallons meaning it's reading way below what's in the tank. But sometimes it would read higher.

Currently trying to look up the process for removing the sending unit, hopefully it's as easy as the xj. I would say the alternator because they literally make shifted a fit to work with a different alternator from a random car at a junk year that has a similar look. Dumb I know... It was the previous owner, the car ran fine and now I'm left to clean this car up to tip top shape

 

Looks like the fuel sender comes thro the top//remove back seat and parcel shelf ..then remove the speaker or cover cut the metal from the hole towards the back seat and peal it back like a sardine tin . This gives access ...take it out and off you go . replace the fuel pump while you are in there as only $30