So the past couple times I’ve been on the trails I have had the AT Oil Temp light come on when slowly climbing hills. Note that this has only happend on offroading trips. The truck will climb highway grades easily on hot days and I never have any gear shifting issues. The first time it happened, I figured it was due to recently installed headers close to the t case cooler so I relocated my t-case cooler to the front of the truck. This last weekend i was climbing a trail and the light came on again. Checked the trans fluid and it was pretty low. I had dropped the trans pan about a year ago and did a full flush and I am now realizing I may have over/underfilled and it could have cooked the ATF over time. Anyways, when I got back home I did a drain and refill. I only cracked the drain plug, not sure if I want to do a full flush now. The fluid that I drained out was brownish and smelled burnt. Refilled the transmission with Lucas Oil synthetic ATF (Dex III) since i figured synthetic will help with heat. However, since I did not do a full flush this time, I am not sure if the previous fluid that is still partially in the system was conventional or synthetic. Because this transmission might be a little more fragile now, would this cause any issues if I mixed synthetic and conventional ATF? Still drives just fine around town the past couple days (even better now actually). Anyone recommend any other corrective measures to avoid any further damage to the tranny? I just dont want to grenade this thing since I just emptied my wallet on a SAS.

 

full flush is very risky on an old trans... just a filter and fluid change with oem trans fluid.
I hate to be negative, but your trans is probably toast. I'm so 😞

 

Besides those 2 times it had thrown the light, it still acts perfectly normal though. I think I’ll try to just slowly drain and replce the fluid a little at a time over the next few weeks to see if it can get a decent color again. I guess I was more so concerned with mixing synthetic into it, but Ive already got about 4 quarts of it in there at this point though…

 

Mixing dino and syn fluids should not be an issue so long as they are both Dextron III spec.
You ought to keep changing some out until the color and odor are fresh