Transmission Fluid Maintenance after Cooling System Issues


Claiming to be an Alpha Chassis
Aug 20, 2022
The transmission was replaced 8 or 9 months ago along with a new radiator. Heater core went out shortly after and I had that replaced (big mistake). Heater core started leaking again recently and also had some water pump and thermostat housing issues, I'm not exactly sure what started first. I recently redid the whole cooling system and bypassed the heater core. My fear now is that the remanufactured transmission may have taken some wear and tear. Originally it was shifting really good, but I've noticed it kind of gets that locked up and hot feeling at times. Nothing major, but one time the car had no coolant reservoir fluid or oil. Dip stick was showing no oil at all.

I'm worried that since the car was running hot that it ate up the oil quick. I recnently learned that the transmission cooler is inside the radiator and I'm worried that the transmission fluid may have also burned up some. I also think I should replace the fluid because of break-in. I want to redo the hoses and maybe install a filter as well and change out the fluid. I know I'll need a jack and stands, and few special tools, pump, and to access some car data as well to get everything in temperature range when servicing the fluid.

So if the cooling system was having issues and running low for a period of time, can it also burn up some of that transmission fluid? I'm worried that I need to change the fluid soon. I only have a 2 year warranty on the transmission and I need it to last, not just for me but for whoever may have this car next. Sure I could sell the car but I'd rather fix all problems and have this be a reliable car for whoever gets it next. 1st transmission lasted almost 150k miles and it's only had about 15k miles on the new remanufacturered transmission. The shop guy said I don't need to do anything with the fluid, he said just drive it. He just kept saying just drive it and that I don't need to baby it. But I know this guy doesn't give a crap and is lazy af. He would love for my transmission to fail 1 day after the warranty lets up. How immediately do I need to change this fluid? Or am I overthinking this and I can wait on changing the fluid? Or is every mile I put on it damaging the transmission until I change the fluid? Do I need to keep the car below a certain rpm to avoid possible damage? Next car will definitely be a manual for peace of mind.

I know I also need to change the rear differential fluid as well at some point. Should one come first? Will rear differential heat cause more heat on the transmission than the recent cooling system problems?
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How much of an impact does cooling system have on an automatic transmission? Should I be worried that the fluid levels could have been affected? Or is it hard to lose transmission fluid this easily. How fast can some extra heat break it down?