My early (78) Countach has two fuel tanks, with a fill on each side of the car...aka pain in the arssss.
If I filled one side only and walked away, will the fuel level in that tank go down as a result of leveling in both tanks? Basically are they actually connected?

Hi Peter,

yes the tanks have a 'crossover' and should normally equalize. What can happen is the upper vent pipes &/or hoses can become plugged with age slowing or preventing the escape of the air pressure created by the incoming fuel.

HTH's

It's a much bigger pain trying to fill the later cars that have only one filler vent. The pipe that connects the two tanks is not large enough to equalise as fast as you are pumping fuel in, which means that when you think you have filled up, you have in fact only filled one tank. When you first get back in the car, the fuel gauge shows full, but as the tanks gradually equalise, you are lucky if you have got 3/4 of a full load on board.

I have stood at a pump for 15 minutes, trying to slowly squeeze in a few extra drops to get a full load, but the pump finally cut out - I guess they must be on a timer. It's one of the few gripes I have about the car.

I think this is why I'll keep one or two 5gallon containers at home. To top off when I get home.