O.K. guys, I've searched and nobody seems to have encountered this problem. I just bought a 93' sc400 for about $6,000 with 129,000 miles on it. I noticed that when I drive with O/D off for no more than five minutes going about 60mph, I overheat. I am pretty sure this is not normal. I dont make it a habit to drive like this it kinda just happens. Any help would be appreciated. Thanks guys.

 

Have your cooling system checked and / or serviced.
The radiator flow may be restricted.
Fans malfunctioning
Thermostat sticking
Radiator cap defective, cracked seals allowing in air..

 

I know its not the radiator cap because lexus replaced my old one and charged me $170 for a new one and a radiator flush. I'll try to get those other things looked at and let you know the results.