i have a 2003 chevy blazer with 99600 miles on it. I do not see in the service intervals from GM about changing differential oils, but where I change my oil, they try to tell me and I just tell them no. Should I change or not?

 

i would id also do your transmission fluid. i do mine about every 30kish maybe sooner depending on how much i tow with it

 

I just changed all my fluids at 100,00 kilometers (60 odd thousand miles). The rear differential oil was very dark, while the front looked like new. Because the transmission fluid was no longer bright pink, I had the transmission flushed at my local GM dealer. The transmission fluid was completely replaced with an updated version of transmission fluid (Dexron VI) . Because I don,t have the full time 4x4 system, ATF was what I used in the transfer case it also showed up as being a little dark. I understand that if I had the full time 4x4 system a different fluid is necessary to prevent damage to the internal clutches therein. FYI you do not need to add any additives to your rear differential as there are no clutch plates in the positrac system used in our vehicles.

 

With close to 100000 Ixmay not change the trans fluid. Could cause mord problems than you want. If it has been changed regularly then no problem

 

I am sorry but I disagree with you on that statement. There is no way that leaving burned up or used up AFT in trans is a good thing. Look at it this way when you don't change your aft & filter you are only shorting the tranny life! Would you not change your oil for 50k or 100k and expect the motor to last?? I change my AFT & filter every 35k to 40k and I have almost 190k on it. So please do your tranny a favor and change it.

I also change my front & rear diff fuild every 75k I use Mobil1 and I change the transfer case fuild every 50k.

 

Read the whole post. Good that you change it reg. If its burnt,,, well then you already have a problem

 

First of all I did read the "whole post" and I am not trying to be a jerk here but I think you are handing out bad advice with that statement. If you choice to not to change your AFT that is fine it is your truck.

Now your statement would be correct only if the trans is slipping or not shifting correctly because that means the trans is already damaged.

But if the tranny still works correctly "burnt fuild" just means it is past due on being changed. It could mean a few different things. It could mean that it is simple as the AFT is not doing the job it should anymore and the clutchs are slipping alittle more than it should. Which if that is the case fresh AFT will help the clutchs grab better. Because even a new trans has slip in it when the ecm tells it to shift so it shifts smoothly and doesn't break your neck with each shift. So that is how AFT gets wore out and the burnt look and smell.

Now instead of me trying to explain everything AFT does I am going to do a copy and paste here to help explain my point of why you should change your AFT.
Quote "Modern ATF typically contains a wide variety of chemical compounds intended to provide the required properties of a particular ATF specification. Most ATFs contain some combination of additives that improve lubricating qualities, such as anti-wear additives, rust and corrosion inhibitors, detergents, dispersants and surfactants (which protect and clean metal surfaces); kinematic viscosity and viscosity index improvers and modifiers, seal swell additives and agents (which extend the rotational speed range and temperature range of the additives' application); anti-foam additives and anti-oxidation compounds to inhibit oxidation and "boil-off" (which extends the life of the additives' application); cold-flow improvers, high-temperature thickeners, gasket conditioners, pour point depressant and petroleum dye. All ATFs contain friction modifiers !!!" When the friction modifiers are wore out or burnt up it only accelerates the wear going on in the trans.

 

I do agree you should change it IF it has been changed on a regular basis. If it hasnt there is a lot of dirt, crap stuck in the nook and crannies everywhere. Old fluid is actually helping the clutch plates. New fluid is high detergent, will loosen up all the crap and COULD cause that floating around crap to plug up little holes and valves. Burnt oil is from burning clutch plates. Clean fresh fluid COULD make them slip and burn up faster. Just saying, Trans fluid changes are good when done on time. Other people here will agree both ways, until it happens to them

 

^this. I've heard the same, too. The best of course, is to change it regularly, right from the get-go. But if you get a vehicle with a ton of miles, and it's never been changed, I would leave it.

What I've read is that the clutch packs wear, and the friction material is now contained in the fluid. Change out the old fluid with new, slippery fluid, and now you have worn, smooth clutch packs, with the new oil. The transmission slips more, and thus wears out already worn clutches and bands even faster.

To each their own, though. If someone has a high mileage, never had the oil changed transmission here, and changes the fluid, it would be interesting to see how it holds up.

 

Cleburne, most of the time your probably gonna be fine, but I`ve heard horror stories and its happened to me