I was recently given a '89 740 turbo wagon and I also inherited its 'hot start' problem. If the car sits in the sun with 80+ degree ambient temperature, it will not start. Nor will it start after it has been driven for any length of time without sitting for an hour in a cool place. However, the most unusual piece of this puzzle is that it will start with a jump start from another vehicle, no matter what the temperature. I know that my radiator/inter-cooler cooling fan has seized and needs to be replaced and my instrument cluster temperature gauge not longer registers, I believe because it needs its engine temperature switch replaced. Otherwise the car runs and starts perfectly. The battery is new as is the radio suppression relay, main fuel pump relay and both the in the tank and booster fuel pumps. I am currently at a loss. Thanks!

I forgot to mention that when it does not start, it does not even crank. You can turn the key and all the dummy lights illuminate, but there is no crank. I can hear the fuel pump turn on as well, but it will not even struggle to start. Again, thanks in advance for any help or suggestions.

Hello. Did you get any information on this yet? I have the same exact problem with my 1989 740GL sedan (non turbo).

Hi,

Check for voltage on the starter when the key is turned.
Also check the starter relay (I do not know it's location).