I HAVE owned my 1989 Nissan Skyline since new. It's now done 260,000km, but on hot days the temperature gauge goes to the top of the scale with or without the airconditioning on. I have had dual electric fans installed without improvement. My coolant has been changed and the radiator has been flushed. Do you have you any ideas?
THE R31 Skyline is robust and generally reliable once you've become used to the howling diff. I'd suggest you test for leaks from cylinder to cylinder and from each cylinder to the water jacket. It could be a head gasket leak.