thirsty supra turbo

[wesbam1]

hi, just wondering what the mile per gallon figure is for these its the 89 turbo,I used it for work today about 90 mile round trip I filled the tank to half way and 90 miles later its about 2mm off the bottom white line Its my first 3 litre turbo is this about right? normal my exhaust manifold is leaking on the turbo side , my car also struggles to idle for about 50 secs could the leak affect the idle.