I've had my 1995 Lexus es300 for about a year now and added 10,000 miles on it. It now has 120,000 miles. Recently checked my dipstick (while the car was running) and there are only two markings on it, hot and cold and my transmission fluid was way above hot. My bigger concern is that my transmission fluid is brown. Ever since i noticed this I have been paying close attention to how my transmission shifts. I don't want to call it rough but you can definitely feel each shift and when traveling at about 50 mph and take my foot off the accelerator it suddenly downshifts. I took it to my mechanic and he said not to change the fluid because the new thinner fluid will cause the clutches to slip even more and then he added a transmission fluid additive. Maybe that's why my level is so high. I know the transmission fluid was changed 60,000 miles ago and according to the owners manual it's time for it to be changed again. But if i leave the brown fluid in, how long will my transmission last and if i change it what are my chances of ruining the transmission?

 

To be safe do a drain and fill and see how the transmission reacts, you will be replacing about 1/3rd of the fluid doing this. If you take your mechanics advice and just leave the old fluid in, the transmission will eventually fail for sure.

 

I know brown fluid usually means overheating, is that why the fluid on my dipstick is so high? and will the new fluid overheat as well?

 

Fluid turns colour because of age/friction and also clutch material and metal particles contaminate the fluid. New fluid won't "overheat", make sure you get the level exactly right.