The previous owner said that he had no reason to change the transmission oil

I hope he didn't apply this 'logic' to the rest of the vehicle. A lot of bad experience with the 4L30E comes as a result of towing, they are a bit marginal for that. If you don't tow you don't need an extra cooler. Change the fluid and filter every 30k or so. The fluid level is correct when it runs out with the transmission just warm, and the engine running.

 

Thank you for your reply

 

I have several 2nd gen rodeos and the transmissions have always been a concern. I suggest that the first time you drop the pan to change the filter to add a drain plug and if the fluid is darker than new fluid and depending on how much, just use the drain plug and drain\refill every few thousand miles after the initial dropping of the pan until the fluid color looks closer to the new fluid. When\If the transmission fluid is the same tint as new fluid and looks great, then I would still drain and refill the transmission fluid every other oil change or maybe every third in particular though if the fluid was darker to start with as even dropping\draining the pan, there is still a lot of transmission fluid you can't get out so you have to dilute it over time by changing out what you can. Also, this method is much less likely to break loose any crud that can cause issues with the solenoid and similar passages.

 

BTW, if you do add a drain plug, be aware of where you locate it by checking for interference of the back of the drain plug (internal side) that could occur when re-installing the pan. There are some positions (locations) you could install the drain plug that will interfere with other components which would prevent the trans oil pan from being re-installed.

 

They come factory with a drain plug, not sure what you're talking about.

 

As I was outside checking the mail anyway I glanced underneath of drain that I added was for the smaller pan and I recall the reason was just to drain more of the fluid out each time more easily, and the larger pan does have both the drain and fill. I also recall that installing a drain plug on the smaller pan has to be where it doesn't interfere with what is behind the pan.

 

That makes sense. And yes, that small pan doesn't get drained unless it's removed, so the contents just gets diluted witht he new oil. Good idea to add the drain plug if you have that capability.